![viii
Handbook of Biodegradable Polymers, 2nd Edition
fertility and quality of soil. Being able to count on a niche market (which is already of
significant size), facilitates achieving economies of scale for biodegradable polymers,
resulting in increased possibilities to build integrated local biorefineries dedicated
to medium-high value-added products, demonstrators and flagships required not
only for biodegradable polymers but also for a range of related building blocks and
agricultural chains as a whole. This will also generate new opportunities for traditional
chemistry, by laying down the foundations for the redevelopment and environmental
upgrading of deindustrialised chemical plants.
The change in the perception of biodegradable polymers is evident by simply
considering the trends from 1989 to 2012 in the fields of ‘biodegradable’ (+2,800%
for scientific literature and +1,100% for the sum of World Intellectual Property
Organization (WIPO) patents, European patents (EP) and United States (US) patents)
and ‘biodegradable plastics’ (+1,400% for scientific literature and +4,200% for the
sum of WO, EP and US patents).
The opportunity to utilise renewable raw materials (RRM) in the production of some
of these biodegradable polymers and to reduce the dependency on foreign petroleum
resources, along with the exploitation of new functional properties in comparison
with traditional plastics, has significant benefits. Besides biodegradability, the
technical developments made during the research process could have significant
advantages for the final consumers and could contribute to the solution of technical,
economic and environmental issues in specific market areas.
RRM as industrial feedstocks for the manufacture of chemical substances and
products, such as oils from oilseed crops, starch from cereals and potatoes, and
cellulose from straw and wood, as well as organic waste, have therefore been given
more and more attention over the last few years. By employing physical, chemical
and biochemical processes, these materials can be converted into chemical
intermediates, polymers and speciality chemicals able to replace fossil feedstocks,
thus implying less energy involved during production and a wider range of disposal
options resulting in a lower environmental impact.
Legislative attention able to properly address this issue could become a further
incentive to the development of products from RRM and maximise the environmental,
social and industrial benefits.
Biobased products were, in fact, one of the six sectors included in the 2007 ‘Lead
Market Initiative’ of the European Commission (EC), with the aim of fostering the
emergence of such lead markets with high economic and societal value, focusing
on areas where coordinated policymaking can speed up market development [1].
More recently, in February 2012, the EC launched a new ‘Bioeconomy Strategy’ [2],](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-13-320.jpg)
![ix
Preface
focusing resources and investments in the strategic sector of biobased products, in order
to shift Europe towards a greater and more sustainable use of renewable resources.
In addition, in July 2013, the EC encouraged the creation of a public-private
partnership of Biobased Industries. It includes approximately 70 full members
(EU large and small companies, clusters and organisations) and more than 100
associated members (universities, research and technology organisations, associations,
European trade organisations and European technology platforms) from the fields of
technology, industry, agriculture and forestry, with the shared commitment to invest
in collaborative research, development and demonstration of biobased technologies.
A supportive and coordinated European strategy for an increased market uptake
would help many biobased products, among them biodegradable biopolymers, to
accelerate reaching economies of scale, in order to attract investments and generate
sustainable economic growth. The EU bioeconomy already has a turnover of
nearly €2 trillion and employs more than 22 million people, 9% of the total
employment in the EU. Each euro invested in EU-funded bioeconomy research
and innovation, with a coherent and incentivising framework, is estimated
to trigger €10 of added value in bioeconomy sectors by 2025 [2]. It is also
estimated that this growth will be enhanced with the development of the model
of integrated biorefineries for the production of high value-added products,
such as biobased chemicals and materials. Biorefineries will process a variety of
biomass-based feedstocks, and the necessary growth in biomass production is
expected to increase the turnover and employment of the seed sector by 10%,
resulting in 5,000 extra jobs [3].
The significant increase in the importance of innovative biopolymers is linked to
the achievement of high-quality standards.
The quality of biodegradable products is assured not only by the control of the
biodegradability parameters but also by the assessment of real functionality. A
biodegradable product is useless if it does not perform as a traditional product
or better in terms of mechanical resistance, duration and so on. For this reason,
the commitment of producers of biodegradable biopolymers in the creation of a
quality network able to guarantee the standards of the product, in all the steps
of the life cycle, becomes very relevant.
The elaboration and diffusion of best practices in the field of organic waste
collection, where the use of biodegradable compostable bags is a tool to improve
the quality of the system, has for example, permitted thousands of municipalities
all over Europe to implement the proposed model. In fact, it has been demonstrated
that, despite the heterogeneity of anaerobic digestion technologies and processing](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-14-320.jpg)
![x
Handbook of Biodegradable Polymers, 2nd Edition
conditions, an efficient and optimised treatment of municipal biowaste, collected with
compostable bioplastic bags, allows preserving the advantages given by the bags in the
collection phase and to secure the most efficient treatment of the collected feedstock
enabling the highest input and minimum production of residues.
The cooperation with public bodies is also a key factor in the success of
biodegradable biopolymers, because the topics under discussion are strictly related
to public interest, such as safety, environment and health.
The implementation of appropriate environmental policies in key areas (like waste
collection) can become a further incentive to the development of products from RRM
and can maximise the environmental, social and industrial advantages. Together
with the intensification of investment, as well as research and development actions
in the biodegradable polymers sector, it would be possible to create a network of
partnerships among stakeholders of the entire supply chain, from agriculture to waste
management, and thereby promote new models of development towards higher levels
of sustainability and cultural growth.
Today, biodegradable biopolymers a r e available on the market, at different
levels of development, and are mainly carbohydrate-based materials. Starch can
be physically modified and used alone or in combination with other polymers,
or it can be used as a substrate for the fermentation and production of
polyhydroxyalkanoates or lactic acid, is then transformed into polylactic acid
through standard polymerisation processes. An alternative option is represented
by vegetable oil-based polymers.
Despite the constant growth of the market, the land use for bioplastics currently
represents just 0.006% of the global agricultural area (which means around
300,000 ha out of 5 billion ha) and it is expected to rise to 0.022% by 2016 (that
is, 1.1 million ha). Meanwhile, the increase in the efficiency of feedstock and
agricultural technology is continuously enhancing good agricultural practices
[4]; moreover, recent trends have focused on the use of marginal lands or
contaminated soils and residues.
The increasing use of bioplastics has opened entirely new generations of materials
with new performances in comparison with traditional plastics. The possibility
offered by physically modified starch to create functionalised nanoparticles able
to modify the properties of natural and synthetic rubbers and other synthetic
polymers, the naturally high oxygen barrier of starch and its derivatives, and
their high permeability to water vapour already offer a range of completely new
solutions to the plastic industry.](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-15-320.jpg)
![1
Maarten van der Zee
1.1 Introduction
This chapter presents an overview of the current knowledge on experimental methods
for monitoring the biodegradability of polymeric materials. The focus is, in particular,
on the biodegradation of materials under environmental conditions. Examples of
in vivo degradation of polymers used in biomedical applications are not covered in
detail, but have been extensively reviewed elsewhere, e.g., [1−3]. Nevertheless, it is
important to realise that the degradation of polymers in the human body is also often
referred to as biodegradation.
A number of different aspects of assessing the potential, rate and degree of
biodegradation of polymeric materials are discussed. The mechanisms of polymer
degradation and erosion are reviewed, and factors affecting enzymatic and
nonenzymatic degradation are briefly addressed. Particular attention is given to the
various ways of measuring biodegradation, including complete mineralisation to gases
(such as carbon dioxide (CO2) and methane (CH4)), water and possibly microbial
biomass. Finally, some general conclusions are presented with respect to measuring
the biodegradability of polymeric materials.
1.2 Background
There is a worldwide research effort to develop biodegradable polymers for agricultural
applications or as a waste management option for polymers in the environment.
Until the end of the 20th
century, most of the efforts were synthesis oriented and not
much attention was paid to the identification of environmental requirements for, and
testing of, biodegradable polymers. Consequently, many unsubstantiated claims of
biodegradability were made, which has damaged the general acceptance.
An important factor is that the term biodegradation has not been applied consistently.
1
Methods for Evaluating the
Biodegradability of Environmentally
Degradable Polymers](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-34-320.jpg)
![2
Handbook of Biodegradable Polymers, 2nd Edition
In the medical field of sutures, bone reconstruction and drug delivery, the term
biodegradation has been used to indicate degradation into macromolecules that stay in
the body but migrate (e.g., ultrahigh molecular weight (MW) polyethylene (PE) from
joint prostheses), or hydrolysis into low MW molecules that are excreted from the body
(bioresorption), or dissolving without modification of the MW (bioabsorption) [4, 5].
On the other hand, for environmentally degradable plastics, the term biodegradation
may mean fragmentation, loss of mechanical properties, or sometimes degradation
through the action of living organisms [6]. Deterioration or loss in physical integrity
is also often mistaken for biodegradation [7]. Nevertheless, it is essential to have a
universally acceptable definition of biodegradability to avoid confusion as to where
biodegradable polymers can be used in agriculture or fit into the overall plan of
polymer waste management. Many groups and organisations have endeavoured to
clearly define the terms ‘degradation’, ‘biodegradation’ and ‘biodegradability’. But
there are several reasons why establishing a single definition among the international
community has not been straightforward, including:
• The variability of an intended definition given the different environments in which
the material is to be introduced and its related impact on those environments.
• The differences of opinion with respect to the scientific approach or reference
points used for determining biodegradability.
• The divergence of opinion concerning the policy implications of various definitions.
• Challenges posed by language differences around the world.
As a result, many different definitions have officially been adopted, depending on
the background of the defining organisation and their particular interests. However,
of more practical importance are the criteria for calling a material ‘biodegradable’.
A demonstrated potential of a material to biodegrade does not say anything about
the time frame in which this occurs, nor the ultimate degree of degradation. The
complexity of this issue is illustrated by the following common examples.
Low-density PE has been shown to biodegrade slowly to CO2 (0.35% in 2.5 years)
[8] and according to some definitions can thus be called a biodegradable polymer.
However, the degradation process is so slow in comparison with the application rate
that accumulation in the environment will occur. The same applies for polyolefin-
starch blends which rapidly lose strength, disintegrate and visually disappear if
exposed to microorganisms [9−11]. This is due to utilisation of the starch component,
but the polyolefin fraction will nevertheless persist in the environment. Can these
materials be called ‘biodegradable’?](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-35-320.jpg)
![3
Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers
1.3 Defining ‘Biodegradability’
In 1992, an international workshop on biodegradability was organised to bring
together experts from around the world to achieve areas of agreement on definitions,
standards and testing methodologies. Participants came from manufacturers,
legislative authorities, testing laboratories, environmentalists and standardisation
organisations in Europe, USA and Japan. Since this fruitful meeting, there is a general
agreement concerning the following key points [12]:
• For all practical purposes of applying a definition, material manufactured to be
biodegradable must relate to a specific disposal pathway such as composting,
sewage treatment, denitrification and anaerobic sludge treatment.
• The rate of degradation of a material manufactured to be biodegradable has to
be consistent with the disposal method and other components of the pathway
into which it is introduced, such that accumulation is controlled.
• The ultimate end products of the aerobic biodegradation of a material manufactured
to be biodegradable are CO2, water and minerals, and the intermediate products
should include biomass and humic materials. (Anaerobic biodegradation was
discussed in less detail by the participants).
• Materials must biodegrade safely and not negatively impact the disposal process
or use of the end product of the disposal.
As a result, specified periods of time, specific disposal pathways and standard test
methodologies were incorporated into definitions. Standardisation organisations
such as the European Committee for Standardization, International Organization for
Standardization (ISO) and American Society for Testing and Materials (ASTM) were
consequently encouraged to rapidly develop standard biodegradation tests so these
could be determined. Society further demanded nondebatable criteria for the evaluation
of the suitability of polymeric materials for disposal in specific waste streams such as
composting or anaerobic digestion. Biodegradability is usually just one of the essential
criteria, besides ecotoxicity, effects on waste treatment processes and so on.
In the following sections of this chapter, the biodegradation of polymeric materials
is looked upon from the chemical perspective. The chemistry of the key degradation
process is represented by Equations 1.1 and 1.2, where CPOLYMER represents either
a polymer or a fragment from any of the degradation processes defined earlier. For
simplicity, the polymer or fragment is considered to be composed only of carbon,
hydrogen and oxygen; other elements may, of course, be incorporated in the polymer,
and these would appear in an oxidised or reduced form after biodegradation depending
on whether the conditions are aerobic or anaerobic, respectively:](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-36-320.jpg)
![4
Handbook of Biodegradable Polymers, 2nd Edition
Aerobic biodegradation:
CPOLYMER + O2 → CO2 + H2O + CRESIDUE + CBIOMASS (1.1)
Anaerobic biodegradation:
CPOLYMER → CO2 + CH4 + H2O + CRESIDUE + CBIOMASS (1.2)
Complete biodegradation occurs when no residue remains and complete mineralisation
is established when the original substrate, CPOLYMER in this example, is completely
converted into gaseous products and salts. However, mineralisation is a very
slow process under natural conditions because some of the polymer undergoing
biodegradation will initially be turned into biomass [13, 14]. Therefore, complete
biodegradation and not mineralisation is the measurable goal when assessing removal
from the environment.
1.4 Mechanisms of Polymer Degradation
When working with biodegradable materials, the obvious question is why some
polymers biodegrade and others do not. To understand this, one needs to know
about the mechanisms through which polymeric materials are biodegraded.
Although biodegradation is usually defined as degradation caused by biological
activity (especially enzymatic action), it will usually occur simultaneously with −
and is sometimes even initiated by − abiotic degradation such as photodegradation
and simple hydrolysis. The following section gives a brief introduction to the most
important mechanisms of polymer degradation.
1.4.1 Nonbiological Degradation of Polymers
A great number of polymers are subject to hydrolysis, such as polyesters,
polyanhydrides, polyamides, polycarbonates, polyurethanes (PU), polyureas,
polyacetals and polyorthoesters. Different mechanisms of hydrolysis have been
extensively reviewed; not only for backbone hydrolysis, but also for the hydrolysis](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-37-320.jpg)
![5
Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers
of pendant groups [15−17]. The necessary elements for a wide range of catalysis,
such as acids and bases, cations, nucleophiles and micellar and phase transfer agents,
are usually present in most environments. In contrast to enzymatic degradation,
where a material is degraded gradually from the surface inwards (primarily because
macromolecular enzymes cannot diffuse into the interior of the material), chemical
hydrolysis of a solid material can take place throughout its cross-section, except for
very hydrophobic polymers.
Important features affecting chemical polymer degradation and erosion include: a) the
type of chemical bond, b) the pH, c) the temperature, d) the copolymer composition
and e) water uptake (hydrophilicity). These features will not be discussed here, but
have been covered in detail by [4].
1.4.2 Biological Degradation of Polymers
Polymers represent major constituents of living cells which are most important for
metabolism (enzyme proteins, storage compounds), genetic information (nucleic
acids) and the structure (cell wall constituents, proteins) of cells [18]. These polymers
have to be degraded inside cells in order to be available for environmental changes
and to other organisms upon cell lysis. It is therefore not surprising that organisms,
during many millions of years of adaptation, have developed various mechanisms
to degrade naturally occurring polymers. However, for the many new and varied
synthetic polymers that have found their way into the environment only in the last
70 years, these mechanisms may not as yet have been developed.
There are many different degradation mechanisms that combine synergistically in
nature to degrade polymers. Microbiological degradation can take place through
the action of enzymes or by-products (such as acids and peroxides) secreted by
microorganisms (bacteria, yeasts, fungi and so on). In addition, macroorganisms can
eat and, sometimes, digest polymers and cause mechanical, chemical or enzymatic
ageing [19, 20].
Two key steps occur in the microbial polymer degradation process: first, a
depolymerisation or chain cleavage step, and second, mineralisation. The first step
normally occurs outside the organism due to the size of the polymer chain and the
insoluble nature of many of the polymers. Extracellular enzymes are responsible for
this step, acting in either an endo (random cleavage on the internal linkages of the
polymer chains) or exo (sequential cleavage on the terminal monomer units in the
main chain) manner.](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-38-320.jpg)
![6
Handbook of Biodegradable Polymers, 2nd Edition
Once oligomeric or monomeric fragments of a sufficiently small size are formed, they
are transported into the cell where they are mineralised. At this stage the cell usually
derives metabolic energy from the mineralisation process. The products of this process,
apart from adenosine triphosphate (ATP), are gases (e.g., CO2, CH4, nitrogen (N2)
and hydrogen (H2)), water, salts and minerals, and biomass. Many variations of this
general view of the biodegradation process can occur, depending on the polymer, the
organisms and the environment. Nevertheless, there will always be, at one stage or
another, the involvement of enzymes.
Enzymes are biological catalysts which can induce enormous (108
−1020
fold) increases
in reaction rates in an environment otherwise unfavourable for chemical reactions. All
enzymes are proteins, i.e., polypeptides with a complex three-dimensional structure,
ranging in MW from several thousand to several million g/mol. Enzyme activity is
closely related to the conformational structure, which creates certain regions at the
surface, forming an active site. The interaction between an enzyme and substrate takes
place at the active site, leading to the chemical reaction, eventually giving a particular
product. Some enzymes contain regions with absolute specificity for a given substrate
while others can recognise a series of substrates. For optimal activity most enzymes
must associate with cofactors, which can be of inorganic (e.g., metal ions) or organic
origin (such as coenzyme A, ATP and vitamins such as riboflavin and biotin) [18].
Different enzymes can have different mechanisms of catalysis. Some enzymes change
the substrate through some free radical mechanism, while others follow alternative
chemical routes. When assessing the biodegradability of polymeric materials, it is
important to realise that there are an enormous amount of different enzymes − each
catalysing its own unique reaction on groups of substrates or on very specific chemical
bonds; in some cases acting complementarily, in others synergistically.
1.5 Measuring the Biodegradation of Polymers
As can be imagined from the various mechanisms described above, biodegradation
does not only depend on the chemistry of the polymer, but also on the presence of the
biological systems involved in the process. When investigating the biodegradability
of a material, the effect of the environment cannot be neglected. Microbial activity,
and hence biodegradation, is influenced by:
• The presence of microorganisms.
• The availability of oxygen.
• The amount of available water.](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-39-320.jpg)
![7
Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers
• The temperature.
• The chemical environment (pH, electrolytes and so on).
In order to simplify the overall picture, the environments in which biodegradation
occurs are basically divided in two: a) aerobic (with oxygen available) and b) anaerobic
(no oxygen present). The availability of oxygen greatly affects the composition of
the microbial community that is active in the environment, and thus its ability to
biodegrade particular polymers. This division can in turn be subdivided into 1) aquatic
and 2) high solids environments. Figure 1.1 schematically presents the different
environments, with examples in which biodegradation may occur [21, 22].
1) Aquatic 2) High solids
a) Aerobic
• Aerobic wastewater treatment plants
• Surface waters; e.g., lakes and rivers
• Marine environments
• Surface soils
• Organic waste composting plants
• Littering
b) Anaerobic
•
Anaerobic wastewater treatment
plants
• Rumen of herbivores
• Deep-sea sediments
• Anaerobic sludge
•
Anaerobic digestion/
biogasification
• Landfill
Figure 1.1 Schematic classification of different biodegradation environments for
polymers
The high solids environments will be the most relevant for measuring environmental
biodegradation of polymeric materials, since they represent the conditions during
biological municipal solid waste treatment, such as composting or anaerobic digestion
(biogasification). However, possible applications of biodegradable materials other
than in packaging and consumer products, e.g., in fishing nets at sea, or undesirable
exposure in the environment due to littering, explain the necessity of aquatic
biodegradation tests.
Numerous ways for the experimental assessment of polymer biodegradability have
been described in the scientific literature. Because of slightly different definitions or
interpretations of the term ‘biodegradability’, the different approaches are therefore
not equivalent in terms of information they provide or practical significance. Since
the typical exposure environment involves incubation of a polymer substrate with
microorganisms or enzymes, only a limited number of measurements are possible:](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-40-320.jpg)
![8
Handbook of Biodegradable Polymers, 2nd Edition
those pertaining to the substrates, to the microorganisms or to the reaction products.
Four common approaches available for studying biodegradation processes have been
reviewed in detail by Andrady [13, 14]:
• Monitoring the accumulation of biomass.
• Monitoring the depletion of substrates.
• Monitoring the reaction products.
• Monitoring the changes in substrate properties.
In the following sections, different test methods for the assessment of polymer
biodegradability are presented. Measurements are usually based on one of the four
approaches given above, but combinations also occur. Before choosing an assay to
simulate environmental effects in an accelerated manner, it is critical to consider the
closeness of fit that the assay will provide between substrate, microorganisms or
enzymes, and the application or environment in which biodegradation should take
place [23].
1.5.1 Enzyme Assays
1.5.1.1 Principle
In enzyme assays, the polymer substrate is added to a buffered or pH-controlled
system, containing one or several types of purified enzymes. These assays are very
useful in examining the kinetics of depolymerisation, or oligomer or monomer release
from a polymer chain under different assay conditions. The method is very rapid
(minutes to hours) and can give quantitative information. However, enzyme assays
are not suitable to determine mineralisation rates.
1.5.1.2 Applications
The type of enzyme to be used, and quantification of degradation, will depend on
the polymer being screened. For example, Mochizuki and co-workers [24] studied
the effects of the draw ratio of polycaprolactone fibres on enzymatic hydrolysis by
lipase. The degradability of polycaprolactone fibres was monitored by dissolved
organic carbon (DOC) formation and weight loss. Similar systems with lipases have
been used for studying the hydrolysis of broad ranges of aliphatic polyesters [25−30],
copolyesters with aromatic segments [26, 31−33] and copolyesteramides [34, 35].](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-41-320.jpg)
![9
Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers
Other enzymes such as α-chymotrypsin and α-trypsin have also been applied to
these polymers [36, 37]. The biodegradability of polyvinyl alcohol (PVA) segments,
with respect to block length and stereo chemical configuration, has been studied
using isolated PVA-dehydrogenase [38]. Cellulolytic enzymes have been used to
study the biodegradability of cellulose ester derivatives as a function of the degree of
substitution and substituent size [39]. Similar work has been performed with starch
esters using amylolytic enzymes such as α-amylases, β-amylases, glucoamylases
and amyloglucosidases [40]. Enzymatic methods have also been used to study the
biodegradability of starch plastics or packaging materials containing cellulose [41−46].
1.5.1.3 Drawbacks
Caution must be used in extrapolating enzyme assays as a screening tool for different
polymers since the enzymes have been paired to only one polymer. The initially selected
enzymes may show significantly reduced activity towards modified polymers or
different materials, even though more suitable enzymes may exist in the environment.
Caution must also be used if the enzymes are not purified or appropriately stabilised
or stored, since inhibition and loss of enzyme activity can occur [23].
1.5.2 Plate Tests
1.5.2.1 Principle
Plate tests were initially developed in order to assess the resistance of plastics to
microbial degradation. Several methods have been standardised by standardisation
organisations such as the ASTM and the ISO [47−49]. They are now also used to
see if a polymeric material will support growth [23, 50]. The principle of the method
involves placing the test material on the surface of a mineral salts agar in a Petri dish
containing no additional carbon source. The test material and agar surface are sprayed
with a standardised mixed inoculum of known bacteria and/or fungi.
The test material is examined, after a predetermined incubation period at constant
temperature, for the amount of growth on its surface and a rating is given.
1.5.2.2 Applications
Potts [51] used the method in his screening of 31 commercially available polymers for
biodegradability. Other studies, where the growth of either mixed or pure cultures of](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-42-320.jpg)
![10
Handbook of Biodegradable Polymers, 2nd Edition
microorganisms is taken to be indicative of biodegradation, have been reported [6].
The validity of this type of test and the use of visual assessment alone, for all plastics,
has been questioned by Seal and Pantke [52]. They recommended that mechanical
properties should be assessed to support visual observations. Microscopic examination
of the surface can also give additional information.
A variation of the plate test is the ‘clear zone’ technique [53], sometimes used to screen
polymers for biodegradability. A fine suspension of polymer is placed in an agar gel
as the sole carbon source and the test inoculum is placed in wells bored into the agar.
After incubation, a clear zone around the well, detected visually or instrumentally, is
indicative of utilisation of the polymer. The method has, for example, been used in
the case of starch plastics [54], various polyesters [55−57] and PU [58].
1.5.2.3 Drawbacks
A positive result in an agar plate test indicates that an organism can grow on the
substrate, but does not mean that the polymer is biodegradable, since growth may
be on contaminants, on plasticisers which are present, on oligomeric fractions still
present in the polymer and so on. Therefore, these tests should be treated with caution
when extrapolating the data to field situations.
1.5.3 Respiration Tests
1.5.3.1 Principle
Aerobic microbial activity is typically characterised by the utilisation of oxygen.
Aerobic biodegradation requires oxygen for the oxidation of compounds to its mineral
constituents, such as CO2, H2O, sulfur dioxide (SO2), phosphorous pentoxide (P2O5)
and so on. The amount of oxygen utilised during incubation, also called the biological
oxygen demand (BOD), is therefore a measure of the degree of biodegradation. Several
test methods are based on measurement of the BOD, often expressed as a percentage
of the theoretical oxygen demand (TOD) of the compound. The TOD, which is the
theoretical amount of oxygen necessary for completely oxidising a substrate to its
mineral constituents, can be calculated by considering the elemental composition and
the stoichiometry of oxidation [13, 59−62] or based on experimental determination
of the chemical oxygen demand (COD) [13, 63].](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-43-320.jpg)
![11
Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers
1.5.3.2 Applications
The closed bottle BOD tests were designed to determine the biodegradability of
detergents [61, 64]. These have stringent conditions due to the low level of inoculum
(in the order of 105
microorganisms/l) and the limited amount of test substance that
can be added (normally between 2 and 4 mg/l). These limitations originate from the
practical requirement that the oxygen demand should not exceed half the maximum
dissolved oxygen level in the water at the temperature of the test, to avoid the
generation of anaerobic conditions during incubation.
For nonsoluble materials, such as polymers, less stringent conditions are acceptable
and alternative ways for measuring BOD were developed. Two-phase (semi) closed
bottle tests enable a higher oxygen content in the flasks and permit a higher inoculum
level. Higher test concentrations are also possible, encouraging higher accuracy with
the direct weighing in of samples. The oxygen demand can alternatively be determined
by periodically measuring the oxygen concentration in the aquatic phase by opening
the flasks [60, 65−67], by measuring the change in volume or pressure in incubation
flasks containing CO2-absorbing agents [59, 68, 69], or by measuring the quantity
of oxygen produced (electrolytically) to maintain a constant gas volume/pressure in
specialised respirometers [59, 62, 65, 66, 68].
1.5.3.3 Suitability
BOD tests are sensitive and relatively simple to perform, and are therefore often used
as screening tests. However, the measurement of oxygen consumption is a nonspecific,
indirect measure for biodegradation and is not suitable for determining anaerobic
degradation. The requirement for test materials to be the sole carbon/energy source for
microorganisms in the incubation media eliminates the use of oxygen measurements
in complex natural environments.
1.5.4 Gas (CO2 or CH4) Evolution Tests
1.5.4.1 Principle
The evolution of CO2 or CH4 from a substrate represents a direct parameter
of mineralisation. Therefore, gas evolution tests can be important tools in the
determination of the biodegradability of polymeric materials. A number of well-
known test methods have been standardised for aerobic biodegradation, such as the
(modified) Sturm test [70−75] and the laboratory controlled composting test [76−79];](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-44-320.jpg)
![12
Handbook of Biodegradable Polymers, 2nd Edition
as well as for anaerobic biodegradation, such as the anaerobic sludge test [80, 81] and
the anaerobic digestion test [82, 83]. Although the principle of these test methods is
the same, they may differ in medium composition, inoculum, the way substrates are
introduced, and in the technique for measuring gas evolution.
1.5.4.2 Applications
Anaerobic tests generally follow biodegradation by measuring the increase in pressure
and/or volume due to gas evolution, usually in combination with gas chromatographic
analysis of the gas phase [84, 85]. Most aerobic standard tests apply continuous
aeration; the exit stream of air can be directly analysed continuously using a
CO2 monitor (usually infrared detectors) or titrimetrically after sorption in dilute
alkali. The cumulative amount of CO2 generated, expressed as a percentage of the
theoretically expected value for total conversion to CO2, is a measure of the extent of
mineralisation achieved. A value of 60% carbon conversion to CO2, achieved within
28 days, is generally taken to indicate ready degradability. Taking into account that in
this system there will also be incorporation of carbon into the formation of biomass
(growth), the 60% value for CO2 implies almost complete degradation. While this
criterion is meant for water-soluble substrates, it is probably applicable to very finely
divided moderately degradable polymeric materials as well [13]. Nevertheless, most
standards for determining the biodegradability of plastics consider a maximum test
duration of 6 months.
Besides the continuously aerated systems, described above, several static respirometers
have been described. Bartha and Pramer [86] describe a two-flask system; one flask,
containing a mixture of soil and the substrate, is connected to another chamber
holding a quantity of CO2 sorbant. Care must be taken to ensure that enough oxygen
is available in the flask for biodegradation. Nevertheless, this experimental set-up
and modified versions thereof have been successfully applied in the assessment of the
biodegradability of polymer films and food packaging materials [87−89].
The percentage of carbon converted to biomass instead of CO2 depends on the
type of polymer and the phase of degradation. Therefore, it has been suggested to
regard the complete carbon balance to determine the degree of degradation [90].
This implies that besides the detection of gaseous carbon, the amount of carbon in
soluble and solid products also needs to be determined. Soluble products, oligomers
of different molecular size, intermediates and proteins secreted from microbial
cells can be measured as COD or as DOC. Solid products, biomass, and polymer
remnants require a combination of procedures to separate and detect different
fractions. The protein content of the insoluble fraction is usually determined to
estimate the amount of carbon converted to biomass, using the assumptions that](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-45-320.jpg)
![13
Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers
dry biomass consists of 50% protein and that the carbon content of dry biomass
is 50% [90−92].
1.5.4.3 Suitability
Gas evolution tests are popular test methods because they are sensitive and relatively
simple to perform. A direct measure for mineralisation is determined and water-soluble
or insoluble polymers can be tested as films, powders or objects. Furthermore, the
test conditions and inoculum can be adjusted to fit the application or environment
in which biodegradation should take place. Aquatic synthetic media is usually used,
but also natural seawater [93, 94] or soil samples [86, 88, 89, 95] can be applied as
biodegradation environments. A prerequisite for these media is that the background
CO2 evolution is limited, which excludes the application of real composting conditions.
Biodegradation under composting conditions is therefore measured using an inoculum
derived from matured compost with low respiration activity [76−78, 96, 97].
A drawback of using complex degradation environments, such as mature compost,
is that the simultaneous characterisation of intermediate degradation products and
determination of the carbon balance is difficult due to the presence of a great number
of interfering compounds. To overcome this, an alternative test was developed based
on an inoculated mineral bed-based matrix [98, 99].
1.5.5 Radioactively Labelled Polymers
1.5.5.1 Principle and Applications
Some materials tend to degrade very slowly under stringent test conditions without
an additional source of carbon. However, if readily available sources of carbon
are added, it becomes impossible to tell how much of the evolved CO2 can be
attributed to decomposition of the plastic. The incorporation of radioactive 14
C in
synthetic polymers gives a means of distinguishing between CO2 or CH4 produced
via metabolism of the polymer, and that generated by other carbon sources in the
test environment. By comparison of the amount of radioactive 14
CO2 or 14
CH4 to the
original radioactivity of the labelled polymer, it is possible to determine the percent by
weight of carbon in the polymer which was mineralised during the exposure period
[51, 100−102]. Collection of radioactively labelled gases or low MW products can
also provide extremely sensitive and reproducible methods to assess the degradation
of polymers with low susceptibility to enzymes, such as PE [8, 103] and cellulose
acetates [104, 105].](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-46-320.jpg)
![14
Handbook of Biodegradable Polymers, 2nd Edition
1.5.5.2 Drawbacks
Problems with handling the radioactively labelled materials and their disposal are
issues on the down side of this method. In addition, in some cases it is difficult to
synthesise the target polymer with the radioactive labels in the appropriate locations,
with representative MW, or with representative morphological characteristics.
1.5.6 Laboratory-scale Simulated Accelerating Environments
1.5.6.1 Principle
Biodegradation of a polymer material is usually associated with changes in the
physical, chemical and mechanical properties of the material. It is indeed these
changes, rather than the chemical reactions, which make the biodegradation process
so interesting from an application point of view. These useful properties might be
measured as a function of the duration of exposure to a biotic medium, to follow the
consequences of the biodegradation process on material properties. Biotic media can
be specifically designed at laboratory scale to mimic natural systems whilst allowing
maximum control of variables such as temperature, pH, microbial community,
mechanical agitation and supply of oxygen. Regulating these variables improves the
reproducibility and may accelerate the degradation process. Laboratory simulations
can also be used for the assessment of long-term effects, achieved by continuous
dosing, on the activity and environment of the disposal system [50].
1.5.6.2 Applications
The Organisation for Economic Co-operation and Development’s ‘Coupled Unit’ test
[106] simulates an activated sludge sewage treatment system, but its application for
polymers would be difficult as DOC is the parameter used to assess biodegradability.
Krupp and Jewell [107] described well-controlled anaerobic and aerobic aquatic
bioreactors to study the degradation of a range of commercially available polymer
films. A relatively low loading rate of the semicontinuous reactors and a long retention
time were maintained to maximise the biodegradation efficiency. Experimental
set-ups have also been designed to simulate marine environments [108], soil burial
conditions [108−110], composting environments [111−116], and landfill conditions
[117−119] at laboratory scale, with controlled parameters such as temperature and
moisture level, and a synthetic waste to provide a standardised basis for comparing
the degradation kinetics of films.](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-47-320.jpg)
![15
Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers
A wide choice of material properties can be followed during the degradation process.
However, it is important to select one which is relevant to the end-use of the polymer
material or provides fundamental information about the degradation process.
Weight loss is a parameter frequently followed because it clearly demonstrates the
disintegration of a biodegradable product [120−122]. Tensile properties are also
often monitored, due to interest in the use of biodegradable plastics in packaging
applications [54, 123, 124]. In those polymers where biodegradation involves a
random scission of the macromolecular chains, a decrease in the average MW and a
general broadening of the MW distribution provide initial evidence of a breakdown
process [86, 125, 126]. However, no significant changes in material characteristics
may be observed in recovered material if the mechanism of biodegradation involves
bioerosion, i.e., enzymatic or hydrolytic cleavage at the surface. Visual examination
of the surface with various microscopic techniques can also give information on the
biodegradation process [115, 127−130]. Likewise, chemical and/or physical changes
in the polymer may be followed by (combinations of) specific techniques such as
infrared [10, 131] or ultraviolet (UV) spectroscopy [84, 132], nuclear magnetic
resonance measurements [115, 126−133], X-ray diffractometry [115, 134, 135] and
differential scanning calorimetry (DSC) [115, 136, 137].
1.5.6.3 Drawbacks
An inherent drawback in the use of mechanical properties, weight loss, MW, or
any other property which relies on the macromolecular nature of the substrate
is that in spite of their sensitivity, these can only address the early stages of the
biodegradation process. Furthermore, these parameters give no information on the
extent of mineralisation. Especially in material blends or copolymers, the hydrolysis
of one component can cause significant disintegration (and thus loss of weight and
tensile properties) whereas other components may persist in the environment, even
in a disintegrated form [13]. Blends of starch, poly(3-hydroxy butyrate) or poly(ε-
caprolactone) with polyolefins are examples of such systems [11, 43, 138].
1.5.7 Natural Environments, Field Trials
Exposure in natural environments provides the best true measure of the environmental
fate of a polymer, because these tests include a diversity of organisms and achieve
a desirable natural closeness of fit between the substrate, microbial agent and the
environment. However, the results of that particular exposure are only relevant to
the specific environment studied, which is likely to differ substantially from many
other environments. An additional problem is the timescale for this method, since
the degradation process, depending on the environment, may be very slow (months](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-48-320.jpg)
![16
Handbook of Biodegradable Polymers, 2nd Edition
to years) [23]. Moreover, little information on the degradation process can be gained
other than the real time required for weight loss or total disintegration. Nevertheless,
field trials in natural environments are still used to extrapolate results acquired in
laboratory tests to biodegradation behaviour under realistic outdoor conditions [115,
116, 127, 139, 140].
1.6 Conclusions
The overview presented above makes clear that there is no such thing as a single
optimal method for determining the biodegradation of polymeric materials. First of all,
the biodegradation of a material is not only determined by the chemical composition
and corresponding physical properties, but the degradation environment, to which the
material is exposed, also affects the rate and degree of biodegradation. Furthermore,
the method or test to be used depends on what information is requested; especially as
the biodegradation concept is very important in relation to the end of life of a material,
while it could be just one aspect of health and environmental safety in other cases.
It is fairly obvious, but often neglected, that one should always consider why a
particular polymeric material should be (or not be) biodegradable when contemplating
how to assess its biodegradability. After all, it is the intended application of the material
that governs the most suitable testing environment, the parameters to be measured
during exposure and the corresponding limit values. For example, investigating
whether biodegradation of a plastic material designed for food packaging could
facilitate undesired growth of (pathogenic) microorganisms requires a completely
different approach from investigating whether its waste can be discarded via
composting (i.e., whether it degrades sufficiently rapidly to be compatible with existing
biowaste composting facilities).
It is important to state that it will not be sufficient to ascertain macroscopic
changes, such as weight loss and disintegration, or growth of microorganisms, to
define a material as biodegradable because these observations may originate from
a partial biodegradation or from the degradation of a component of the material
itself. In order to study the real biodegradation of a material in the environment
(composting, anaerobic digestion, soil and water) it is necessary to determine
the mineralisation, which is the transformation of the material into: CO2, CH4
(anaerobic condition), water and new biomass. Furthermore, it is important to
evaluate the eventual toxic effects that the addition of the material could have
on the environment, in order to avoid introducing dangerous substances. In
this way we will be sure that no harm will be caused to the environment itself.
This is the same approach followed by the principal standardisation bodies with
standards regarding the compostability of plastics and packaging. These standards](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-49-320.jpg)
![TESTIMONY OF THE CATACOMBS TO SOME OF THE
SACRAMENTS.
In a former article,[31]
whilst following Mr. Withrow and other
Protestant controversialists through their evasions and
misinterpretations of the evidence to be found in the Catacombs on
behalf of certain points of Catholic doctrine and practice, we pointed
out that prayers either for the dead or to them were the only two
articles on which it would be reasonable to look for information from
the inscriptions on the gravestones. We said that these prayers were
likely to find expression, if anywhere, by the side of the grave. As
they took their last look on the loved remains of their deceased
friend or relative, the affectionate devotion of the survivors would
naturally give utterance either to a hearty prayer for the everlasting
happiness of him they had lost, or to a piteous cry for help, an
earnest petition that he would continue to exercise, in whatever way
might be possible under the conditions of his new mode of
existence, that same loving care and protection which had been their
joy and support during his life; or sometimes both these prayers
might be poured forth together, according as the strictness of God’s
justice, or the Christian faith and virtues of the deceased, happened
to occupy the foremost place in the petitioner’s thoughts.
When, therefore, we proceeded in a second paper to question the
same subterranean sanctuaries on another subject of Christian
doctrine—the supremacy of St. Peter—we called into court another
set of witnesses altogether: to wit, the paintings of their tombs and
chapels. Exception has been taken against the competency of these
witnesses, on the plea that they are not old enough; they were not
contemporary, it is said, with those first ages of the church whose
faith is called in question. To this we answer that the objection is](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-72-320.jpg)
![centuries which tell us that the deceased was a neophyte, or newly
illuminated—which means the same thing: viz., that he had been
lately baptized—or that he had lived so many months or years after
he had received the initiatory sacrament of the Christian covenant.
Occasionally, also, a faint reference may be found to another
sacrament—the Sacrament of Confirmation. This was often, or even
generally, administered in olden times immediately after baptism, of
which it was considered the complement and perfection. “From time
immemorial,” says Tertullian (ab immemorabili), “as soon as we have
emerged from the bath [of regeneration] we are anointed with the
holy unction.” Hence it is sometimes doubtful which sacrament is
intended, or rather it is probable that it was intended to include both
under the words inscribed on the epitaphs—the verbs accepit,
percepit, consecutus est (the same as we find in the fathers of the
same or an earlier age), used for the most part absolutely, without
any object whatever following them; but in one or two cases fidem
or gratiam sanctum are used. An epitaph of a child three years old
adds: Consecuta est D. vi. Deposita viii. Kal. Aug. Another says
simply: Pascasius percepit xi. Kal. Maias; and a third: Crescentia q. v.
a. xxxiii. Accepit iii. Kal. Jul. A fourth records of a lady that she died
at the age of thirty-five: Ex die acceptionis suæ vixit dies lvii.; to
which we append another: Consecutus est ii. Non. Decemb. ex die
consecutionis in sæculo fuit ad usque vii. Idas Decemb. This last
inscription is taken from a Christian cemetery in Africa, not in Rome;
but it was worth quoting for its exact conformity with the one which
precedes it. In both alike there is the same distinction between the
natural and the spiritual age of the deceased—i.e., between his first
and his second birth. After stating the number of years he had lived
in the world, his age is computed afresh from the day of his
regeneration, thus marking off the length of his spiritual from that of
his merely animal life.
A Greek inscription was found a few years since on the Via Latina,
recording of a lady who had belonged to one of the Gnostic sects in
the third century, that she had been “anointed in the baths of Christ
with his pure and incorruptible ointment”—an inscription which](https://image.slidesharecdn.com/25873922-250521063832-0bb28264/85/Handbook-Of-Biodegradable-Polymers-2nd-Edition-Bastioli-C-Ed-82-320.jpg)
Handbook Of Biodegradable Polymers 2nd Edition Bastioli C Ed
- 1. Handbook Of Biodegradable Polymers 2nd Edition Bastioli C Ed download https://ebookbell.com/product/handbook-of-biodegradable- polymers-2nd-edition-bastioli-c-ed-51747844 Explore and download more ebooks at ebookbell.com
- 2. Here are some recommended products that we believe you will be interested in. You can click the link to download. Handbook Of Biodegradable Polymers 3rd Edition Catia Bastioli Editor https://ebookbell.com/product/handbook-of-biodegradable-polymers-3rd- edition-catia-bastioli-editor-50933024 Handbook Of Biodegradable Polymers Bastioli C Ed https://ebookbell.com/product/handbook-of-biodegradable-polymers- bastioli-c-ed-51747816 Handbook Of Biodegradable Polymers 3rd Edition Bastioli C Ed https://ebookbell.com/product/handbook-of-biodegradable-polymers-3rd- edition-bastioli-c-ed-52181162 Handbook Of Biodegradable Polymers Synthesis Characterization And Applications 1st Edition Andreas Lendlein https://ebookbell.com/product/handbook-of-biodegradable-polymers- synthesis-characterization-and-applications-1st-edition-andreas- lendlein-2358836
- 3. Handbook Of Polymers For Pharmaceutical Technologies Volume 3 Biodegradable Polymers Kumar Thakur https://ebookbell.com/product/handbook-of-polymers-for-pharmaceutical- technologies-volume-3-biodegradable-polymers-kumar-thakur-5300942 Handbook Of Biodegradable Materials Gomaa A M Ali Abdel Salam H Makhlouf https://ebookbell.com/product/handbook-of-biodegradable-materials- gomaa-a-m-ali-abdel-salam-h-makhlouf-49168932 Handbook Of Biopolymers And Biodegradable Plastics Sina Ebnesajjad https://ebookbell.com/product/handbook-of-biopolymers-and- biodegradable-plastics-sina-ebnesajjad-4411604 Handbook Of Composites From Renewable Materials Biodegradable Materials Kessler https://ebookbell.com/product/handbook-of-composites-from-renewable- materials-biodegradable-materials-kessler-6625100 Handbook Of Psychology Developmental Psychology Richard M Lerner M A Easterbrooks Jayanthi Mistry https://ebookbell.com/product/handbook-of-psychology-developmental- psychology-richard-m-lerner-m-a-easterbrooks-jayanthi-mistry-44869188
- 5. Handbook of Biodegradable Polymers, 2nd Edition Editor: Catia Bastioli
- 6. iv Handbook of Biodegradable Polymers, 2nd Edition
- 7. Handbook of Biodegradable Polymers, 2nd Edition Editor: Catia Bastioli A Smithers Group Company Shawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.polymer-books.com
- 8. First Published in 2014 by Typeset by Argil Services ISBN: 978-1-84735-526-3 (hardback) 978-1-84735-527-0 (softback) 978-1-84735-528-7 (ebook) Every effort has been made to contact copyright holders of any material reproduced within the text and the author and publishers apologise if any have been overlooked. A catalogue record for this book is available from the British Library. All rights reserved. Except as permitted under current legislation no part of this publication may be photocopied, reproduced or distributed in any form or by any means or stored in a database or retrieval system, without the prior permission from the copyright holder. ©Smithers Information Ltd., 2014 Smithers Rapra Technology Ltd Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK
- 9. iv A cknowledgments I would like to thank all the contributors to this volume for their time, patience and effort in producing this book. Special and sincere thanks go to Federica Mastroianni for her extensive effort, which went beyond the handling of the considerable correspondence associated with the book and organisation of the reviewing process. I would like to express my appreciation to all the staff of Smithers Rapra for the high- quality support provided during all stages of the production of this book. Thanks are also extended to Gian Tomaso Masala for his reviewing of the chapter references. Finally, I wish to dedicate this volume to the memory of Raul Gardini, who was a pioneer of Bioeconomy, and the unwitting origin of my interest and dedication to renewable raw materials and bioplastics.
- 10. v P reface ‘The great problem of packaging, which every experienced chemist knows, was well known to God Almighty, who solved it brilliantly, as he is wont to, with cellular membranes, eggshells, the multiple peel of oranges, and our own skins, because after all we too are liquids. Now, at that time there did not exist polyethylene, which would have suited me perfectly since it is flexible, light and splendidly impermeable: but it is also a bit too incorruptible, and not by chance God Almighty himself, although he is a master of polymerisation, abstained from patenting it: He does not like incorruptible things.’ I find this extract from Primo Levi’s book ‘The Periodic Table’, the best introduction to biodegradable polymers. The durability of conventional plastics is a serious environmental drawback when these materials are used in applications with little probability of recycling, when recycling happens to be too expensive, or when plastics have a high probability of contaminating the natural environment or organic waste. In these, and only in these applications, biodegradable polymers really make the difference. Biodegradable polymers must not be a simple replacement for traditional plastics. They must be used as an opportunity to redesign applications by focusing on the efficient use of resources and tending towards the elimination of waste, by transforming local issues into business opportunities and by developing a systemic vision to counterbalance the management culture that has contributed to the dissipative growth model we are now living in. The fundamental criterion needed to avoid any aggravation of this situation, and indeed to reverse the trend, is the efficient use of resources, being aware that only a type of growth which could restore its central focus on local areas, a knowledge economy, the cascading model, and the absence of waste and rejects, will lead to continuous and harmonious growth. A similar approach requires the selection of standards which have to go beyond products and towards systems. The objective should not be to maximise market
- 11. vi Handbook of Biodegradable Polymers, 2nd Edition volumes but to boost local regeneration from an environmental, social and economic viewpoint, promoting a cultural leap towards a system-based economy and shared trust among the different stakeholders. For this purpose, the quality rules for biodegradable polymers have to be strict and guarantee, besides compostability and biodegradability in different environments, nontoxicity of products and additives, as well as a low environmental impact throughout the life cycle, with improving targets in terms of raw material quality and renewability level, feedstock sustainability, inuse efficiency and end of life options to close the loop. Over the past 30 years, increasing effort has been dedicated to developing polymers designed to be biologically degraded in selected environmental conditions. In particular, industrial research has focused on discovering and developing biodegradable polymers that are, at the same time, easily processable, exhibit good performance and are cost-competitive (considering both internal and external costs) with conventional polymers. When bioplastics are biodegradable according to European Norms 13432 − the European reference for the technical material manufacturers, public authorities, composters, certifiers and consumers − or its equivalents the American Society for Testing and Materials D6400, or International Organization for Standardization 14855, they can, besides other disposal options, be organically recycled through composting. Such characteristics, when composting infrastructures are available, may therefore represent a significant advantage in sectors like waste collection, catering or packaging which have a high probability of being contaminated by food, or ending up in organic waste or nature: in such cases, organic recycling must be preferred to mechanical recycling. The property of a plastic to biodegrade in household compost permits its disposal in widespread composting infrastructures, at the same time optimising the quality of organic waste and maximising its diversion from landfill. The ability of a plastic to biodegrade via composting is also proof that its chemical structure is intrinsically biodegradable. Significant literature shows that the most widespread compostable bioplastics, currently available on the market, are also able to fully biodegrade in soil and even in the marine environment or through home composting. A range of standards are also available to certify the behaviour of these bioplastics in many different environments. The present volume reviews the most important achievements, the programmes and approaches of institutions, the private sector and universities to develop biodegradable polymers, and it explores their potential in depth. The volume covers: the most relevant biodegradable polymers of renewable and nonrenewable origin, the present business situation, a review of the main studies on their environmental impact and a critical analysis of the methodologies involved, the potential of new
- 12. vii Preface areas such as biocatalysis in the development of new renewable building blocks for biodegradable polymers, the expansion of the biorefinery concept towards integrated biorefineries, and the main policy and funding initiatives recently undertaken at the European Union (EU) level to foster the innovation capacity in Europe and to favour the market entry of innovative biobased and biodegradable products. It also takes into consideration aspects related to the biodegradation of these polymers in different environments and the related standards and case studies (including the interactions of biodegradable items with different anaerobic digestion technologies), showing their use in helping to solve specific solid waste problems. The demand for biodegradable polymers has steadily grown over the last 10 years, at an annual rate of between 20−30%, in regions where composting infrastructures are well developed and the separate collection of organic waste is well established. Wherever the separate collection of biowaste is in place (and this is an unwavering trend in the EU), all the traditional short life pollutants of organic waste (when it is with polyethylene, renewable or not) are critical, because they are not biodegradable. The organic recycling of biowaste requires plastic-free streams in order to assure high recycling rates. The existing link between the increasing use of biodegradable polymers and the efficient infrastructures for organic recycling and the separate collection of organic waste can be perceived as a limitation to the fast growth of this class of material. Instead it represents a unique opportunity to reconnect the solution of long-lasting environmental problems to local growth and regional regeneration putting into practice the knowledge-based economy. The Italian case study presented in the book curated by Walter Ganapini ‘Bioplastics: A Case Study of Bioeconomy in Italy’ shows how biodegradable polymers can be a powerful catalyst for the activation of local area regeneration. The book is dedicated to the Italian approach for resolving the problem of disposable carrier bags. It is all about transforming a category of waste which presents extremely critical issues (high surface area-volume ratio, large number of articles produced, the fact that the bags, if dispersed, cannot be reabsorbed into the environment, and marine pollution) into an opportunity, in order to solve an even more pressing problem; that of organic waste being sent to landfill. A small number of disposable carrier bags, if coupled with reusable bags, and made from biodegradable, compostable plastics, can be reused as valuable resources in organic waste collection. This makes them a powerful and important means of intercepting organic waste, with no expense required from local councils, helping to achieve the objective of improving the quantity and quality of organic waste: a feedstock that is important for the future development of the bioeconomy, and for the
- 13. viii Handbook of Biodegradable Polymers, 2nd Edition fertility and quality of soil. Being able to count on a niche market (which is already of significant size), facilitates achieving economies of scale for biodegradable polymers, resulting in increased possibilities to build integrated local biorefineries dedicated to medium-high value-added products, demonstrators and flagships required not only for biodegradable polymers but also for a range of related building blocks and agricultural chains as a whole. This will also generate new opportunities for traditional chemistry, by laying down the foundations for the redevelopment and environmental upgrading of deindustrialised chemical plants. The change in the perception of biodegradable polymers is evident by simply considering the trends from 1989 to 2012 in the fields of ‘biodegradable’ (+2,800% for scientific literature and +1,100% for the sum of World Intellectual Property Organization (WIPO) patents, European patents (EP) and United States (US) patents) and ‘biodegradable plastics’ (+1,400% for scientific literature and +4,200% for the sum of WO, EP and US patents). The opportunity to utilise renewable raw materials (RRM) in the production of some of these biodegradable polymers and to reduce the dependency on foreign petroleum resources, along with the exploitation of new functional properties in comparison with traditional plastics, has significant benefits. Besides biodegradability, the technical developments made during the research process could have significant advantages for the final consumers and could contribute to the solution of technical, economic and environmental issues in specific market areas. RRM as industrial feedstocks for the manufacture of chemical substances and products, such as oils from oilseed crops, starch from cereals and potatoes, and cellulose from straw and wood, as well as organic waste, have therefore been given more and more attention over the last few years. By employing physical, chemical and biochemical processes, these materials can be converted into chemical intermediates, polymers and speciality chemicals able to replace fossil feedstocks, thus implying less energy involved during production and a wider range of disposal options resulting in a lower environmental impact. Legislative attention able to properly address this issue could become a further incentive to the development of products from RRM and maximise the environmental, social and industrial benefits. Biobased products were, in fact, one of the six sectors included in the 2007 ‘Lead Market Initiative’ of the European Commission (EC), with the aim of fostering the emergence of such lead markets with high economic and societal value, focusing on areas where coordinated policymaking can speed up market development [1]. More recently, in February 2012, the EC launched a new ‘Bioeconomy Strategy’ [2],
- 14. ix Preface focusing resources and investments in the strategic sector of biobased products, in order to shift Europe towards a greater and more sustainable use of renewable resources. In addition, in July 2013, the EC encouraged the creation of a public-private partnership of Biobased Industries. It includes approximately 70 full members (EU large and small companies, clusters and organisations) and more than 100 associated members (universities, research and technology organisations, associations, European trade organisations and European technology platforms) from the fields of technology, industry, agriculture and forestry, with the shared commitment to invest in collaborative research, development and demonstration of biobased technologies. A supportive and coordinated European strategy for an increased market uptake would help many biobased products, among them biodegradable biopolymers, to accelerate reaching economies of scale, in order to attract investments and generate sustainable economic growth. The EU bioeconomy already has a turnover of nearly €2 trillion and employs more than 22 million people, 9% of the total employment in the EU. Each euro invested in EU-funded bioeconomy research and innovation, with a coherent and incentivising framework, is estimated to trigger €10 of added value in bioeconomy sectors by 2025 [2]. It is also estimated that this growth will be enhanced with the development of the model of integrated biorefineries for the production of high value-added products, such as biobased chemicals and materials. Biorefineries will process a variety of biomass-based feedstocks, and the necessary growth in biomass production is expected to increase the turnover and employment of the seed sector by 10%, resulting in 5,000 extra jobs [3]. The significant increase in the importance of innovative biopolymers is linked to the achievement of high-quality standards. The quality of biodegradable products is assured not only by the control of the biodegradability parameters but also by the assessment of real functionality. A biodegradable product is useless if it does not perform as a traditional product or better in terms of mechanical resistance, duration and so on. For this reason, the commitment of producers of biodegradable biopolymers in the creation of a quality network able to guarantee the standards of the product, in all the steps of the life cycle, becomes very relevant. The elaboration and diffusion of best practices in the field of organic waste collection, where the use of biodegradable compostable bags is a tool to improve the quality of the system, has for example, permitted thousands of municipalities all over Europe to implement the proposed model. In fact, it has been demonstrated that, despite the heterogeneity of anaerobic digestion technologies and processing
- 15. x Handbook of Biodegradable Polymers, 2nd Edition conditions, an efficient and optimised treatment of municipal biowaste, collected with compostable bioplastic bags, allows preserving the advantages given by the bags in the collection phase and to secure the most efficient treatment of the collected feedstock enabling the highest input and minimum production of residues. The cooperation with public bodies is also a key factor in the success of biodegradable biopolymers, because the topics under discussion are strictly related to public interest, such as safety, environment and health. The implementation of appropriate environmental policies in key areas (like waste collection) can become a further incentive to the development of products from RRM and can maximise the environmental, social and industrial advantages. Together with the intensification of investment, as well as research and development actions in the biodegradable polymers sector, it would be possible to create a network of partnerships among stakeholders of the entire supply chain, from agriculture to waste management, and thereby promote new models of development towards higher levels of sustainability and cultural growth. Today, biodegradable biopolymers a r e available on the market, at different levels of development, and are mainly carbohydrate-based materials. Starch can be physically modified and used alone or in combination with other polymers, or it can be used as a substrate for the fermentation and production of polyhydroxyalkanoates or lactic acid, is then transformed into polylactic acid through standard polymerisation processes. An alternative option is represented by vegetable oil-based polymers. Despite the constant growth of the market, the land use for bioplastics currently represents just 0.006% of the global agricultural area (which means around 300,000 ha out of 5 billion ha) and it is expected to rise to 0.022% by 2016 (that is, 1.1 million ha). Meanwhile, the increase in the efficiency of feedstock and agricultural technology is continuously enhancing good agricultural practices [4]; moreover, recent trends have focused on the use of marginal lands or contaminated soils and residues. The increasing use of bioplastics has opened entirely new generations of materials with new performances in comparison with traditional plastics. The possibility offered by physically modified starch to create functionalised nanoparticles able to modify the properties of natural and synthetic rubbers and other synthetic polymers, the naturally high oxygen barrier of starch and its derivatives, and their high permeability to water vapour already offer a range of completely new solutions to the plastic industry.
- 16. xi Preface The use of RRM, however, is not by itself a guarantee of low environmental impact. Aspects such as the production processes, the technical performance and the weight of each final product, and its disposal options, have to be carefully considered along all the steps of the product’s life. The engineering of biobased materials for specific applications using life cycle analysis in a cradle-to-grave approach is therefore a critical aspect. The involvement of upstream players, that is farmers and their associations, is a very important prerequisite. In agriculture, new agronomical approaches and the development of new genotypes for nonfood applications should be taken into consideration. Agricultural crops and processes associated with lower environmental impact and lower costs are important factors in the development of new biobased products. Effort must also be made at the industrial level in order to develop less expensive and higher performance products and low-impact technologies. Policies should therefore be focused more on supporting innovation and scale up of new technologies which can create solid added value and are capable of responding to the societal challenges faced by our planet. The involvement of specific stakeholders can be achieved if a communication programme is launched and operated in parallel with industrial activities. The success of the project is very much linked to the diffusion of a new environmental awareness, at all levels: politicians, public administrators, investors, associations, customers, non-governmental organisations (NGO),citizens and society at large, all of them must be reached by specific communications, in order to initiate a comprehensive and coherent sustainable strategy, with positive effects in the local areas involved. This, in turn, must give rise to specific legislative actions in order to quantify the social and environmental benefits linked to the nonfood use of agricultural and natural raw materials, and to the bioconversion of waste materials into industrial products. References 1. A Lead Market Initiative for Europe − COM(2007) 860 Final, Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions.
- 17. xii Handbook of Biodegradable Polymers, 2nd Edition 2. Innovating for Sustainable Growth: A Bioeconomy for Europe − COM(2012) 60 Final, Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions. 3. The Bio-based Industries Vision – Accelerating Innovation and Market Uptake of Bio-based Products, Vision Document of the Bio-based Industries Consortium − European Public-Private Partnership on Bio-Based Industries. http://biconsortium.eu/sites/default/files/downloads/BIC_BBI_Vision_web. pdf, July 2012, p. 15. 4. European Bioplastics, Bioplastics − Facts and Figures. http://en.european-bioplastics.org/wp-content/uploads/2013/publications/ EuBP_FactsFigures_bioplastics_2013.pdf, 2013, p. 5.
- 18. xiii C ontents 1 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers. .................................................................................. 1 1.1 Introduction. .................................................................................... 1 1.2 Background..................................................................................... 1 1.3 Defining ‘Biodegradability’.............................................................. 3 1.4 Mechanisms of Polymer Degradation.............................................. 4 1.4.1 Nonbiological Degradation of Polymers............................. 4 1.4.2 Biological Degradation of Polymers.................................... 5 1.5 Measuring the Biodegradation of Polymers. ..................................... 6 1.5.1 Enzyme Assays. ................................................................... 8 1.5.1.1 Principle. ............................................................... 8 1.5.1.2 Applications. ......................................................... 8 1.5.1.3 Drawbacks. ........................................................... 9 1.5.2 Plate Tests........................................................................... 9 1.5.2.1 Principle. ............................................................... 9 1.5.2.2 Applications. ......................................................... 9 1.5.2.3 Drawbacks. ......................................................... 10 1.5.3 Respiration Tests. .............................................................. 10 1.5.3.1 Principle. ............................................................. 10 1.5.3.2 Applications. ....................................................... 11 1.5.3.3 Suitability........................................................... 11 1.5.4 Gas (CO2 or CH4 ) Evolution Tests. .................................. 11 1.5.4.1 Principle. ............................................................. 11 1.5.4.2 Applications. ....................................................... 12
- 19. xiv Handbook of Biodegradable Polymers, 2nd Edition 1.5.4.3 Suitability........................................................... 13 1.5.5 Radioactively Labelled Polymers. ...................................... 13 1.5.5.1 Principle and Applications.................................. 13 1.5.5.2 Drawbacks. ......................................................... 14 1.5.6 Laboratory-scale Simulated Accelerating Environments.... 14 1.5.6.1 Principle. ............................................................. 14 1.5.6.2 Applications. ....................................................... 14 1.5.6.3 Drawbacks. ......................................................... 15 1.5.7 Natural Environments, Field Trials................................... 15 1.6 Conclusions................................................................................... 16 2 Biodegradation Behaviour of Polymers in Liquid Environments................ 29 2.1 Introduction. .................................................................................. 29 2.2 Degradation in Real Liquid Environments..................................... 30 2.2.1 Degradation in Freshwater and Marine Environment....... 31 2.2.1.1 Polyhydroxyalkanoates....................................... 31 2.2.1.2 Synthetic Polyesters. ............................................ 32 2.3 Degradation in Laboratory Tests Simulating Real Aquatic Environments. ................................................................................ 34 2.3.1 Aerobic Liquid Environments........................................... 34 2.3.2 Anaerobic Liquid Environments....................................... 37 2.4 Degradation in Laboratory Tests with Optimised and Defined Liquid Media................................................................................. 41 2.5 Standard Tests for Biodegradable Polymers using Liquid Media.... 44 2.6 Summary....................................................................................... 49 3 Environmental Fate and Ecotoxicity Assessment of Biodegradable Polymers................................................................................................... 55 3.1 Introduction. .................................................................................. 55 3.2 End of Life Scenarios of Biodegradable Polymers. .......................... 57 3.2.1 Biodegradation End Products. ........................................... 57
- 20. Contents xv 3.2.2 Biodegradation during Organic Recycling. ........................ 58 3.2.2.1 Industrial Composting........................................ 58 3.2.2.2 Home Composting. ............................................. 60 3.2.2.3 Anaerobic Digestion........................................... 60 3.2.3 Biodegradation in Soil. ...................................................... 60 3.2.3.1 Soil Texture and Structure. .................................. 61 3.2.3.2 Water Content.................................................... 61 3.2.3.3 Organic Matter................................................... 61 3.2.3.4 pH ..................................................................... 61 3.2.3.5 Temperature. ....................................................... 62 3.2.3.6 Oxygen............................................................... 62 3.2.3.7 Sunlight.............................................................. 62 3.3 Investigation into Polymer Biodegradation.................................... 62 3.3.1 Standard on Industrial Composting.................................. 63 3.3.2 Identification of the Intermediates of Polymer Biodegradation................................................................. 66 3.4 Environmental Fate of Biodegradation Intermediates. .................... 70 3.4.1 Physico-chemical Properties and Behaviour of Intermediates.................................................................... 71 3.4.1.1 Ready Biodegradability....................................... 71 3.4.1.2 Bioconcentration Factor. ..................................... 75 3.4.2 Ecotoxicological Assessment based on the Environmental Behaviour of the Intermediates................. 76 3.5 Ecotoxicological Assessment of Biodegradation Intermediates....... 78 3.5.1 Aquatic Toxicity............................................................... 78 3.5.1.1 Bacteria. .............................................................. 79 3.5.1.2 Algae.................................................................. 79 3.5.1.3 Crustacea............................................................ 79 3.5.1.4 Fish. .................................................................... 80 3.5.2 Terrestrial Toxicity. ........................................................... 80
- 21. xvi Handbook of Biodegradable Polymers, 2nd Edition 3.5.2.1 Bacteria. .............................................................. 81 3.5.2.2 Invertebrates....................................................... 81 3.5.2.3 Plants. ................................................................. 81 3.5.2.4 Vertebrates. ......................................................... 81 3.6 Discussion and Conclusions........................................................... 82 4 Ecotoxicological Aspects of the Biodegradation Process of Polymers........ 91 4.1 Preface........................................................................................... 91 4.2 The Need for Ecotoxicity Analysis of Biodegradable Materials. ..... 92 4.3 Standards and Regulations for Testing Biodegradable Polymers. .... 93 4.4 Detection of the Influences on an Ecosystem caused by the Biodegradation of Polymers........................................................... 95 4.4.1 Potential Influences of Polymers after Composting........... 96 4.4.2 Potential Influences of Polymers during and after Biodegradation in Soil and Sediment. ................................ 98 4.5 A Short Introduction to Ecotoxicology.......................................... 99 4.5.1 Dose-response Relationships........................................... 100 4.5.2 Investigation Level of Ecotoxicity Tests. .......................... 100 4.5.3 Length of the Exposure Period........................................ 101 4.5.4 End-points...................................................................... 102 4.5.5 The Difference between Toxicity Tests and Bioassays. ..... 102 4.5.6 Ecotoxicity Profile Analysis. ............................................ 103 4.6 Recommendations and Standard Procedures for Biotests............. 103 4.6.1 Bioassays with Higher Plant Species. ............................... 106 4.6.2 Bioassays with Earthworms (Eisenia foetida).................. 108 4.6.3 Preparation of Elutriates for Aquatic Ecotoxicity Tests... 109 4.6.4 Bioassays with Algae. ...................................................... 110 4.6.5 Bioassays with Luminescent Bacteria.............................. 112 4.6.6 Bioassays with Daphnia.................................................. 113 4.6.7 Biotests with Higher Aquatic Plants................................ 113
- 22. Contents xvii 4.7 Evaluation of Bioassay Results Obtained from Samples of Complex Composition................................................................. 114 4.7.1 Testing of Solid Samples. ................................................. 114 4.7.2 Testing of Sediments....................................................... 115 4.8 Special Prerequisites to be Considered when Applying Bioassays for Biodegradable Polymers......................................... 116 4.8.1 Nutrients in the Sample.................................................. 116 4.8.2 Biodegradation Intermediates......................................... 117 4.8.3 Diversity of the Microbial Population............................. 118 4.8.4 Humic Substances........................................................... 120 4.9 Evaluation of Test Results and Limits of Bioassays...................... 121 4.10 Research Results for Ecotoxicity Testing of Biodegradable Polymers...................................................................................... 122 4.10.1 The Relationship between Chemical Structure, Biodegradation Pathways and the Formation of Potentially Ecotoxic Metabolites. .................................... 123 4.10.2 Ecotoxicity of Polymers.................................................. 123 4.10.3 Ecotoxic Effects appearing after Degradation in Compost or after Anaerobic Digestion. ........................... 124 4.10.4 Ecotoxic Effects appearing during Degradation in Soil... 125 4.11 Conclusion. .................................................................................. 128 4.11.1 Consequences of Test Schemes for Investigations on Biodegradable Polymers.................................................. 128 4.11.2 Materials Intended for Organic Recovery....................... 129 4.11.3 Materials Intended for Applications in the Environment.129 4.11.4 Final Statement............................................................... 130 5 International and National Norms on Biodegradability and Certification Procedures.......................................................................... 139 5.1 Introduction. ................................................................................ 139 5.2 Organisations for Standardisation............................................... 141 5.3 Norms on Biodegradation Test Methods. ..................................... 143
- 23. xviii Handbook of Biodegradable Polymers, 2nd Edition 5.3.1 Introduction. ................................................................... 143 5.3.2 Aquatic, Aerobic Biodegradation Tests........................... 146 5.3.2.1 Based on Carbon Conversion (‘Sturm’ Test). ..... 146 5.3.2.2 Based on Oxygen Consumption (‘MITI’ Test). .. 146 5.3.2.3 Other................................................................ 147 5.3.3 Compost Biodegradation Tests. ....................................... 147 5.3.3.1 Controlled Composting Test............................. 147 5.3.3.2 Mineral Bed Composting Test. .......................... 148 5.3.3.3 Other Compost Biodegradation Tests............... 150 5.3.4 Soil Biodegradation Tests................................................ 151 5.3.5 Aquatic, Anaerobic Biodegradation Tests. ....................... 152 5.3.6 High Solids, Anaerobic Biodegradation Tests. ................. 153 5.3.6.1 Landfill Simulation Tests. .................................. 153 5.3.7 Marine Biodegradation Tests.......................................... 154 5.3.8 Other Biodegradation Tests. ............................................ 154 5.4 Norms on Disintegration Test Methods....................................... 155 5.4.1 Introduction. ................................................................... 155 5.4.2 Compost Disintegration Tests......................................... 155 5.4.3 Disintegration in Water. .................................................. 157 5.4.4 Disintegration in other Environments............................. 157 5.5 Norms on Specifications for Degradability. .................................. 158 5.5.1 Introduction. ................................................................... 158 5.5.2 (Industrial) Compostability............................................. 159 5.5.3 (Home) Compostability.................................................. 162 5.5.4 Soil Biodegradability....................................................... 163 5.5.5 Aquatic Biodegradability................................................ 163 5.5.6 Marine Biodegradability................................................. 164 5.5.7 Anaerobic Digestion....................................................... 164 5.5.8 Oxo-degradation............................................................ 164
- 24. Contents xix 5.6 Certification................................................................................. 165 5.6.1 Introduction. ................................................................... 165 5.6.2 (Industrial) Compostability Certification Systems........... 166 5.6.2.1 Seedling............................................................ 166 5.6.2.2 OK Compost.................................................... 167 5.6.2.3 Biodegradable Products Institute Logo. ............. 168 5.6.2.4 Cedar Grove Logo............................................ 169 5.6.2.5 GreenPla Certification System........................... 169 5.6.2.6 The Australasian Seedling Logo and Certification System.......................................... 169 5.6.2.7 Other Certification and Logo Systems. .............. 170 5.6.3 (Home) Compostability Certification Systems. ................ 171 5.6.3.1 OK Compost Home.......................................... 171 5.6.3.2 Other Systems for Home Compostability. ......... 172 5.6.4 Other Biodegradability Certification Systems.................. 173 6 General Characteristics, Processability, Industrial Applications and Market Evolution of Biodegradable Polymers......................................... 175 6.1 General Characteristics................................................................ 175 6.1.1 Polymer Biodegradation Mechanisms............................. 176 6.1.2 Polymer Molecular Size, Structure and Chemical Composition................................................................... 177 6.1.3 Biodegradable Polymer Classes....................................... 178 6.1.4 Natural Biodegradable Polymers. .................................... 178 6.1.4.1 Starch............................................................... 179 6.1.4.2 Polyhydroxyalkanoates..................................... 181 6.1.5 Synthetic Biodegradable Polymers. .................................. 184 6.1.5.1 Polylactic Acid and Polyglycolic Acid............... 184 6.1.5.2 Poly(e-caprolactone)......................................... 186 6.1.5.3 Diol-Diacid Aliphatic Polyesters....................... 187 6.1.5.4 Aliphatic/Aromatic Copolyesters...................... 189
- 25. xx Handbook of Biodegradable Polymers, 2nd Edition 6.1.5.5 Polyvinyl Alcohol. ............................................. 191 6.1.6 Modified, Natural Biodegradable Polymers.................... 192 6.2 Processability............................................................................... 194 6.2.1 Extrusion........................................................................ 196 6.2.2 Film Blowing and Casting............................................... 197 6.2.3 Moulding........................................................................ 198 6.2.4 Fibre Spinning. ................................................................ 199 6.3 Industrial Applications. ................................................................ 200 6.3.1 Compost Bags................................................................. 201 6.3.2 Carrier Bags.................................................................... 202 6.3.3 Mulch Films. ................................................................... 204 6.3.4 Other Applications......................................................... 205 6.4 Market Evolution........................................................................ 206 6.5 Conclusions................................................................................. 210 7 Polyhydroxyalkanoates........................................................................... 219 7.1 Introduction. ................................................................................ 219 7.2 Production of Polyhydroxyalkanoates......................................... 221 7.3 The Various Types of Polyhydroxyalkanoates.............................. 221 7.3.1 Poly(R-3-hydroxybutyrate)............................................. 222 7.3.2 Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).............. 224 7.3.3 Poly(3-hydroxybutyrate-co-4-hydroxybutyrate). ............. 226 7.3.4 Polyhydroxyalkanoates Containing Medium-chain-length Monomers. ................................... 228 7.3.5 Uncommon Constituents of Polyhydroxyalkanoates....... 232 7.4 Mechanisms of Polyhydroxyalkanoate Biosynthesis. .................... 232 7.4.1 Conditions that Promote the Biosynthesis and Accumulation of Polyhydroxyalkanoates in Microorganisms.............................................................. 232 7.4.2 Carbon Sources for the Production of Polyhydroxyalkanoates................................................... 233
- 26. Contents xxi 7.4.3 Biochemical Pathways Involved in the Metabolism of Polyhydroxyalkanoates................................................... 235 7.4.4 The Key Enzyme of the Biosynthesis of Polyhydroxyalkanoates, Polyhydroxyalkanoate Synthase. ......................................................................... 238 7.5 Genetically Modified Systems and other Methods for the Production of Polyhydroxyalkanoates......................................... 239 7.5.1 Recombinant Escherichia coli......................................... 239 7.5.2 Transgenic Plants............................................................ 240 7.5.3 In vitro Production of Polyhydroxyalkanoates. ............... 241 7.6 Biodegradation of Polyhydroxyalkanoates................................... 241 7.7 Applications of Polyhydroxyalkanoates....................................... 243 7.7.1 Biomedical Applications................................................. 244 7.7.2 Industrial Applications. ................................................... 245 7.7.3 Agricultural Applications................................................ 246 7.8 Conclusions and Outlook............................................................ 246 8 Starch-based Technology......................................................................... 265 8.1 Introduction. ................................................................................ 265 8.2 Starch.......................................................................................... 267 8.3 Starch-filled Plastics..................................................................... 270 8.4 Structural Starch Modifications................................................... 271 8.4.1 Starch Gelatinisation and Retrogradation....................... 272 8.4.2 Starch Jet-cooking. .......................................................... 274 8.4.3 Starch Extrusion Cooking............................................... 275 8.4.4 Starch Destructurisation in the Absence of Synthetic Polymers......................................................................... 276 8.4.5 Starch Destructurisation in the Presence of Synthetic Polymers......................................................................... 278 8.4.5.1 Ethylene-acrylic Acid Copolymer...................... 279 8.4.5.2 Ethylene-vinyl Alcohol Copolymers.................. 280 8.4.5.3 Polyvinyl Alcohol. ............................................. 281
- 27. xxii Handbook of Biodegradable Polymers, 2nd Edition 8.4.5.4 Aliphatic Polyesters. .......................................... 282 8.4.5.5 Aliphatic-aromatic Polyesters. ........................... 282 8.4.5.6 Other Polymers................................................. 283 8.4.6 Additional Information on Starch Complexation............ 284 8.5 Starch-based Materials on the Market......................................... 289 8.6 Conclusions................................................................................. 290 9 Lactic Acid-based Degradable Polymers.................................................. 301 9.1 Introduction. ................................................................................ 301 9.2 Main Structural Characteristics of Lactic Acid Stereocopolymers......................................................................... 303 9.3 Synthesis of Lactic Acid-based Polymers...................................... 305 9.4 Main Material Properties............................................................. 308 9.5 Degradation of Lactic Acid-based Polymers................................. 309 9.6 Lactic Acid-based Copolymers..................................................... 312 9.7 Interest in the Biomedical Field.................................................... 312 9.8 Interest as Degradable Polymers in the Environment................... 313 9.9 Interest as Polymers from Renewable Resources.......................... 314 9.10 Conclusion. .................................................................................. 314 10 Biodegradable Polyesters......................................................................... 321 10.1 Introduction. ................................................................................ 321 10.2 Biodegradable Aliphatic Polyesters.............................................. 322 10.2.1 Biodegradable Aliphatic Polyesters with a Hydroxyacid Repetitive Unit.......................................... 322 10.2.1.1 Poly(e-caprolactone)......................................... 322 10.2.1.2 Polyhydroxyalkanoates..................................... 323 10.2.1.3 Polylactic Acid.................................................. 325 10.2.1.4 Polyglycolic Acid.............................................. 327 10.2.1.5 Long Chain Polyhydroxyacid. ........................... 327 10.2.2 Biodegradable Aliphatic Polyesters with a Diol/Dicarboxylic Acid Repetitive Unit........................... 328
- 28. Contents xxiii 10.2.3 Aliphatic Polyesters Biodegradation................................ 331 10.2.4 Properties of Biodegradable Aliphatic Polyesters. ............ 332 10.3 Biodegradable Aliphatic-Aromatic Copolyesters.......................... 332 10.3.1 Ecoflex............................................................................ 336 10.3.1.1 Producer/Patents: BASF AG, Germany. ............. 336 10.3.2 Origo-Bi. ......................................................................... 337 10.3.2.1 Producer/Patents: Novamont............................ 337 10.3.3 Biocosafe 2003F............................................................. 337 10.3.3.1 Producer: Zhejiang Hangzhou Xinfu Pharmaceutical Co. Ltd.................................... 337 10.3.4 S-EnPol........................................................................... 338 10.3.4.1 Producer: Samsung Fine Chemicals................... 338 10.3.5 Properties of Biodegradable Aliphatic-aromatic Copolyesters................................................................... 338 10.3.6 Biodegradation of Aliphatic-aromatic Copolyesters........ 338 10.3.6.1 Polymer-related Parameters Determining Biodegradation................................................. 341 10.3.6.2 Degradation under Composting Conditions. ..... 346 10.3.6.3 Degradation in Soil........................................... 347 10.3.6.4 Degradation in an Aqueous Environment......... 349 10.3.6.5 Degradation under Anaerobic Conditions. ........ 350 10.3.6.6 Fate of Aromatic Sequences and Risk Assessment. ....................................................... 351 10.4 Renewable Monomers for Biodegradable Polyester Synthesis...... 356 11 Material Formed from Proteins............................................................... 369 11.1 Introduction. ................................................................................ 369 11.2 Structure of Material Proteins...................................................... 371 11.3 Protein-based Materials............................................................... 377 11.4 Formation of Protein-based Materials. ......................................... 383 11.4.1 The Solvent Process........................................................ 383
- 29. xxiv Handbook of Biodegradable Polymers, 2nd Edition 11.4.2 The Thermoplastic Process............................................. 387 11.5 Properties of Protein-based Materials.......................................... 396 11.6 Applications. ................................................................................ 403 12 Enzyme Catalysis in the Synthesis of Biodegradable Polymers................. 421 12.1 Introduction. ................................................................................ 421 12.2 Polyester Synthesis....................................................................... 422 12.2.1 Polycondensation of Hydroxyacids and Esters................ 422 12.2.2 Polymerisation of Dicarboxylic Acids or Their Activated Derivatives with Glycols................................. 425 12.2.3 Ring-opening Polymerisation of Carbonates and other Cyclic Monomers.................................................. 435 12.2.4 Ring-opening Polymerisation and Copolymerisation of Lactones..................................................................... 443 12.3 Oxidative Polymerisation of Phenol and Derivatives of Phenol.... 454 12.4 Enzymatic Polymerisation of Polysaccharides.............................. 467 12.5 Conclusions................................................................................. 472 13 Environmental Life Cycle of Biodegradable Plastics................................ 489 13.1 Introduction to Life Cycle Thinking and Assessment................... 489 13.2 Bioplastics and Life Cycle Assessment. ......................................... 494 13.2.1 Biodegradability and Compostability.............................. 495 13.2.2 Renewable Origin........................................................... 498 13.2.3 Optimisation Potential.................................................... 502 13.3 Conclusions................................................................................. 503 14 The use of Biodegradable Polymers for the Optimisation of Models for the Source Separation and Composting of Organic Waste................. 509 14.1 Introduction. ................................................................................ 509 14.1.1 The Development of Composting and Schemes for the Source Separation of Biowaste in Europe: A Matter of Quality....................................................................... 510 14.2 Main Drivers for Composting in the European Union................. 511
- 30. Contents xxv 14.2.1 Directive 99/31/EC on Landfills...................................... 511 14.2.2 The Waste Framework Directive (Directive 2008/98/EC)................................................... 512 14.2.3 Other regulatory and Political Drivers............................ 512 14.3 The Source Separation of Organic Waste: Schemes and Results in the South of Europe................................................................. 513 14.4 ‘Biowaste’, ‘Vegetable, Garden and Fruit’, and ‘Food Waste’: Relevance of a Definition on the Performance of the Waste Management System.................................................................... 516 14.5 The Importance of Biobags.......................................................... 518 14.5.1 Features of ‘Biobags’: The Importance of Biodegradability and its Cost-efficiency.......................... 519 14.6 Cost Assessment of Optimised Schemes....................................... 521 14.6.1 Tools to Optimise the Schemes and their Suitability in Different Situations......................................................... 523 14.6.1.1 Collection Frequency for Residual Waste.......... 524 14.6.1.2 Diversifying the Fleet of Collection Vehicles..... 524 14.7 Conclusions................................................................................. 526 15 Collection of Biowaste with Biodegradable and Compostable Plastic Bags and Treatment in Anaerobic Digestion Facilities: Advantages and Options for Optimisation. ....................................................................... 529 15.1 Introduction. ................................................................................ 529 15.2 Current European Policies regarding Biowaste, Renewable Energy, Emission Reduction and Resource Management............. 530 15.3 The Role of Compostable Plastic Bags in Biowaste Source Separation Schemes. ..................................................................... 532 15.4 Compostable Plastics in Anaerobic Digestion: Standards and Performance. ................................................................................ 534 15.5 Anaerobic Digestion Facilities Treating Biowaste: Technologies, Pretreatment Options and Management of Compostable Plastic Bags............................................................................................. 535 15.5.1 Combined Anaerobic and Aerobic versus Anaerobic Only Processes: Pros and Cons....................................... 535
- 31. xxvi Handbook of Biodegradable Polymers, 2nd Edition 15.5.2 Dry and Wet Technologies.............................................. 537 15.5.3 Different Anaerobic Digestion Technologies and Fate of Compostable Plastic Bags........................................... 538 15.6 Case Studies of Anaerobic Digestion Facilities Managing Biowaste in Compostable Plastic Bags......................................... 540 15.6.1 Case Study 1: Wet Codigestion with a Hydropulper: Compostable Bags can switch from Disposal (Route 3) to Material Recovery (Route 2)...................................... 541 15.6.2 Case Study 2: Wet Digestion with Screw Press/Mash Separation: Compostable Bags Skipping Digestion and going Directly to Material Recovery (Route 2)............... 546 15.6.3 Case Study 3: Dry Plug Flow Digestion: Compostable Bags going Partly to Digestion (Route 1) and Partly to Material Recovery (Route 2). .......................................... 549 15.6.4 Case Study 4: Dry Batch Digestion: Compostable Bags going to Digestion followed by Material Recovery (Route 1)........................................................................ 552 15.7 Conclusions................................................................................. 555 16 Principles, Drivers, and Analysis of Biodegradable and Biobased Plastics.................................................................................................... 561 16.1 Introduction. ................................................................................ 561 16.2 Understanding Biodegradability ñ Biodegradable Compostable Plastics......................................................................................... 562 16.3 Measuring and Reporting Biodegradability. ................................. 563 16.4 International Standards for Biodegradability............................... 566 16.5 Misleading Claims of Biodegradability........................................ 568 16.6 Environmental and Health Consequences.................................... 569 16.7 US Federal Trade Commission Green Guides............................... 569 16.7.1 Degradable and Biodegradable Claims. ........................... 570 16.7.2 Compostable Claims....................................................... 571 16.7.3 Renewable Materials, Biobased Materials and Biobased Content. ........................................................... 572 16.8 Biobased Plastics - Carbon Footprint Reductions using Plant/Biomass Carbon and Value Proposition.............................. 572
- 32. Contents xxvii 16.8.1 Illustrating Zero Material Carbon Footprint using Basic Stoichiometric Calculations................................... 574 16.8.2 Measuring Biobased Carbon Content............................. 576 16.8.3 Calculating and Reporting Biobased Carbon Contents... 577 16.9 Example of Bio Polyethylene Terephthalate................................. 578 16.10 Summary..................................................................................... 578 17 Biorefineries for Renewable Monomers................................................... 583 17.1 Introduction. ................................................................................ 583 17.2 Biorefinery Concepts.................................................................... 583 17.2.1 Starch and Sugar Biorefineries. ........................................ 587 17.2.2 Oilseed Biorefineries....................................................... 588 17.2.3 Green Biorefinery............................................................ 588 17.2.4 Lignocellulose Biorefinery............................................... 590 17.2.5 Aquatic Biorefinery......................................................... 591 17.3 Monomers based on Renewable Raw Materials.......................... 592 17.4 Summary and Outlook................................................................ 601 18 Research and Development Funding with the Focus on Biodegradable Products.................................................................................................. 605 18.1 Introduction. ................................................................................ 605 18.2 Policy Initiatives and Plans in the Field of Biopolymers and their Applications. ................................................................................ 606 18.2.1 The Lead Market Initiative............................................. 606 18.2.2 Key Enabling Technologies............................................. 609 18.2.3 The Innovation Union. .................................................... 610 18.2.4 The Bioeconomy Strategy............................................... 610 18.3 European Union-funded Research on Biopolymers and their Applications. ................................................................................ 611 18.3.1 Why the need for European Union-funded Research?..... 611 18.3.2 The Framework Programmes.......................................... 612
- 33. xxviii Handbook of Biodegradable Polymers, 2nd Edition 18.3.3 Specific Programmes with Focus on Biopolymers and their Applications........................................................... 614 18.4 The Seventh Framework Programme........................................... 622 18.5 Funded Projects: Biopolymers and their Applications.................. 626 18.6 The Eco-innovation Initiative. ...................................................... 627 18.7 Horizon 2020.............................................................................. 628 18.8 Conclusions................................................................................. 629 Abbreviation...................................................................................................... 637 Index ............................................................................................................... 651
- 34. 1 Maarten van der Zee 1.1 Introduction This chapter presents an overview of the current knowledge on experimental methods for monitoring the biodegradability of polymeric materials. The focus is, in particular, on the biodegradation of materials under environmental conditions. Examples of in vivo degradation of polymers used in biomedical applications are not covered in detail, but have been extensively reviewed elsewhere, e.g., [1−3]. Nevertheless, it is important to realise that the degradation of polymers in the human body is also often referred to as biodegradation. A number of different aspects of assessing the potential, rate and degree of biodegradation of polymeric materials are discussed. The mechanisms of polymer degradation and erosion are reviewed, and factors affecting enzymatic and nonenzymatic degradation are briefly addressed. Particular attention is given to the various ways of measuring biodegradation, including complete mineralisation to gases (such as carbon dioxide (CO2) and methane (CH4)), water and possibly microbial biomass. Finally, some general conclusions are presented with respect to measuring the biodegradability of polymeric materials. 1.2 Background There is a worldwide research effort to develop biodegradable polymers for agricultural applications or as a waste management option for polymers in the environment. Until the end of the 20th century, most of the efforts were synthesis oriented and not much attention was paid to the identification of environmental requirements for, and testing of, biodegradable polymers. Consequently, many unsubstantiated claims of biodegradability were made, which has damaged the general acceptance. An important factor is that the term biodegradation has not been applied consistently. 1 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers
- 35. 2 Handbook of Biodegradable Polymers, 2nd Edition In the medical field of sutures, bone reconstruction and drug delivery, the term biodegradation has been used to indicate degradation into macromolecules that stay in the body but migrate (e.g., ultrahigh molecular weight (MW) polyethylene (PE) from joint prostheses), or hydrolysis into low MW molecules that are excreted from the body (bioresorption), or dissolving without modification of the MW (bioabsorption) [4, 5]. On the other hand, for environmentally degradable plastics, the term biodegradation may mean fragmentation, loss of mechanical properties, or sometimes degradation through the action of living organisms [6]. Deterioration or loss in physical integrity is also often mistaken for biodegradation [7]. Nevertheless, it is essential to have a universally acceptable definition of biodegradability to avoid confusion as to where biodegradable polymers can be used in agriculture or fit into the overall plan of polymer waste management. Many groups and organisations have endeavoured to clearly define the terms ‘degradation’, ‘biodegradation’ and ‘biodegradability’. But there are several reasons why establishing a single definition among the international community has not been straightforward, including: • The variability of an intended definition given the different environments in which the material is to be introduced and its related impact on those environments. • The differences of opinion with respect to the scientific approach or reference points used for determining biodegradability. • The divergence of opinion concerning the policy implications of various definitions. • Challenges posed by language differences around the world. As a result, many different definitions have officially been adopted, depending on the background of the defining organisation and their particular interests. However, of more practical importance are the criteria for calling a material ‘biodegradable’. A demonstrated potential of a material to biodegrade does not say anything about the time frame in which this occurs, nor the ultimate degree of degradation. The complexity of this issue is illustrated by the following common examples. Low-density PE has been shown to biodegrade slowly to CO2 (0.35% in 2.5 years) [8] and according to some definitions can thus be called a biodegradable polymer. However, the degradation process is so slow in comparison with the application rate that accumulation in the environment will occur. The same applies for polyolefin- starch blends which rapidly lose strength, disintegrate and visually disappear if exposed to microorganisms [9−11]. This is due to utilisation of the starch component, but the polyolefin fraction will nevertheless persist in the environment. Can these materials be called ‘biodegradable’?
- 36. 3 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers 1.3 Defining ‘Biodegradability’ In 1992, an international workshop on biodegradability was organised to bring together experts from around the world to achieve areas of agreement on definitions, standards and testing methodologies. Participants came from manufacturers, legislative authorities, testing laboratories, environmentalists and standardisation organisations in Europe, USA and Japan. Since this fruitful meeting, there is a general agreement concerning the following key points [12]: • For all practical purposes of applying a definition, material manufactured to be biodegradable must relate to a specific disposal pathway such as composting, sewage treatment, denitrification and anaerobic sludge treatment. • The rate of degradation of a material manufactured to be biodegradable has to be consistent with the disposal method and other components of the pathway into which it is introduced, such that accumulation is controlled. • The ultimate end products of the aerobic biodegradation of a material manufactured to be biodegradable are CO2, water and minerals, and the intermediate products should include biomass and humic materials. (Anaerobic biodegradation was discussed in less detail by the participants). • Materials must biodegrade safely and not negatively impact the disposal process or use of the end product of the disposal. As a result, specified periods of time, specific disposal pathways and standard test methodologies were incorporated into definitions. Standardisation organisations such as the European Committee for Standardization, International Organization for Standardization (ISO) and American Society for Testing and Materials (ASTM) were consequently encouraged to rapidly develop standard biodegradation tests so these could be determined. Society further demanded nondebatable criteria for the evaluation of the suitability of polymeric materials for disposal in specific waste streams such as composting or anaerobic digestion. Biodegradability is usually just one of the essential criteria, besides ecotoxicity, effects on waste treatment processes and so on. In the following sections of this chapter, the biodegradation of polymeric materials is looked upon from the chemical perspective. The chemistry of the key degradation process is represented by Equations 1.1 and 1.2, where CPOLYMER represents either a polymer or a fragment from any of the degradation processes defined earlier. For simplicity, the polymer or fragment is considered to be composed only of carbon, hydrogen and oxygen; other elements may, of course, be incorporated in the polymer, and these would appear in an oxidised or reduced form after biodegradation depending on whether the conditions are aerobic or anaerobic, respectively:
- 37. 4 Handbook of Biodegradable Polymers, 2nd Edition Aerobic biodegradation: CPOLYMER + O2 → CO2 + H2O + CRESIDUE + CBIOMASS (1.1) Anaerobic biodegradation: CPOLYMER → CO2 + CH4 + H2O + CRESIDUE + CBIOMASS (1.2) Complete biodegradation occurs when no residue remains and complete mineralisation is established when the original substrate, CPOLYMER in this example, is completely converted into gaseous products and salts. However, mineralisation is a very slow process under natural conditions because some of the polymer undergoing biodegradation will initially be turned into biomass [13, 14]. Therefore, complete biodegradation and not mineralisation is the measurable goal when assessing removal from the environment. 1.4 Mechanisms of Polymer Degradation When working with biodegradable materials, the obvious question is why some polymers biodegrade and others do not. To understand this, one needs to know about the mechanisms through which polymeric materials are biodegraded. Although biodegradation is usually defined as degradation caused by biological activity (especially enzymatic action), it will usually occur simultaneously with − and is sometimes even initiated by − abiotic degradation such as photodegradation and simple hydrolysis. The following section gives a brief introduction to the most important mechanisms of polymer degradation. 1.4.1 Nonbiological Degradation of Polymers A great number of polymers are subject to hydrolysis, such as polyesters, polyanhydrides, polyamides, polycarbonates, polyurethanes (PU), polyureas, polyacetals and polyorthoesters. Different mechanisms of hydrolysis have been extensively reviewed; not only for backbone hydrolysis, but also for the hydrolysis
- 38. 5 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers of pendant groups [15−17]. The necessary elements for a wide range of catalysis, such as acids and bases, cations, nucleophiles and micellar and phase transfer agents, are usually present in most environments. In contrast to enzymatic degradation, where a material is degraded gradually from the surface inwards (primarily because macromolecular enzymes cannot diffuse into the interior of the material), chemical hydrolysis of a solid material can take place throughout its cross-section, except for very hydrophobic polymers. Important features affecting chemical polymer degradation and erosion include: a) the type of chemical bond, b) the pH, c) the temperature, d) the copolymer composition and e) water uptake (hydrophilicity). These features will not be discussed here, but have been covered in detail by [4]. 1.4.2 Biological Degradation of Polymers Polymers represent major constituents of living cells which are most important for metabolism (enzyme proteins, storage compounds), genetic information (nucleic acids) and the structure (cell wall constituents, proteins) of cells [18]. These polymers have to be degraded inside cells in order to be available for environmental changes and to other organisms upon cell lysis. It is therefore not surprising that organisms, during many millions of years of adaptation, have developed various mechanisms to degrade naturally occurring polymers. However, for the many new and varied synthetic polymers that have found their way into the environment only in the last 70 years, these mechanisms may not as yet have been developed. There are many different degradation mechanisms that combine synergistically in nature to degrade polymers. Microbiological degradation can take place through the action of enzymes or by-products (such as acids and peroxides) secreted by microorganisms (bacteria, yeasts, fungi and so on). In addition, macroorganisms can eat and, sometimes, digest polymers and cause mechanical, chemical or enzymatic ageing [19, 20]. Two key steps occur in the microbial polymer degradation process: first, a depolymerisation or chain cleavage step, and second, mineralisation. The first step normally occurs outside the organism due to the size of the polymer chain and the insoluble nature of many of the polymers. Extracellular enzymes are responsible for this step, acting in either an endo (random cleavage on the internal linkages of the polymer chains) or exo (sequential cleavage on the terminal monomer units in the main chain) manner.
- 39. 6 Handbook of Biodegradable Polymers, 2nd Edition Once oligomeric or monomeric fragments of a sufficiently small size are formed, they are transported into the cell where they are mineralised. At this stage the cell usually derives metabolic energy from the mineralisation process. The products of this process, apart from adenosine triphosphate (ATP), are gases (e.g., CO2, CH4, nitrogen (N2) and hydrogen (H2)), water, salts and minerals, and biomass. Many variations of this general view of the biodegradation process can occur, depending on the polymer, the organisms and the environment. Nevertheless, there will always be, at one stage or another, the involvement of enzymes. Enzymes are biological catalysts which can induce enormous (108 −1020 fold) increases in reaction rates in an environment otherwise unfavourable for chemical reactions. All enzymes are proteins, i.e., polypeptides with a complex three-dimensional structure, ranging in MW from several thousand to several million g/mol. Enzyme activity is closely related to the conformational structure, which creates certain regions at the surface, forming an active site. The interaction between an enzyme and substrate takes place at the active site, leading to the chemical reaction, eventually giving a particular product. Some enzymes contain regions with absolute specificity for a given substrate while others can recognise a series of substrates. For optimal activity most enzymes must associate with cofactors, which can be of inorganic (e.g., metal ions) or organic origin (such as coenzyme A, ATP and vitamins such as riboflavin and biotin) [18]. Different enzymes can have different mechanisms of catalysis. Some enzymes change the substrate through some free radical mechanism, while others follow alternative chemical routes. When assessing the biodegradability of polymeric materials, it is important to realise that there are an enormous amount of different enzymes − each catalysing its own unique reaction on groups of substrates or on very specific chemical bonds; in some cases acting complementarily, in others synergistically. 1.5 Measuring the Biodegradation of Polymers As can be imagined from the various mechanisms described above, biodegradation does not only depend on the chemistry of the polymer, but also on the presence of the biological systems involved in the process. When investigating the biodegradability of a material, the effect of the environment cannot be neglected. Microbial activity, and hence biodegradation, is influenced by: • The presence of microorganisms. • The availability of oxygen. • The amount of available water.
- 40. 7 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers • The temperature. • The chemical environment (pH, electrolytes and so on). In order to simplify the overall picture, the environments in which biodegradation occurs are basically divided in two: a) aerobic (with oxygen available) and b) anaerobic (no oxygen present). The availability of oxygen greatly affects the composition of the microbial community that is active in the environment, and thus its ability to biodegrade particular polymers. This division can in turn be subdivided into 1) aquatic and 2) high solids environments. Figure 1.1 schematically presents the different environments, with examples in which biodegradation may occur [21, 22]. 1) Aquatic 2) High solids a) Aerobic • Aerobic wastewater treatment plants • Surface waters; e.g., lakes and rivers • Marine environments • Surface soils • Organic waste composting plants • Littering b) Anaerobic • Anaerobic wastewater treatment plants • Rumen of herbivores • Deep-sea sediments • Anaerobic sludge • Anaerobic digestion/ biogasification • Landfill Figure 1.1 Schematic classification of different biodegradation environments for polymers The high solids environments will be the most relevant for measuring environmental biodegradation of polymeric materials, since they represent the conditions during biological municipal solid waste treatment, such as composting or anaerobic digestion (biogasification). However, possible applications of biodegradable materials other than in packaging and consumer products, e.g., in fishing nets at sea, or undesirable exposure in the environment due to littering, explain the necessity of aquatic biodegradation tests. Numerous ways for the experimental assessment of polymer biodegradability have been described in the scientific literature. Because of slightly different definitions or interpretations of the term ‘biodegradability’, the different approaches are therefore not equivalent in terms of information they provide or practical significance. Since the typical exposure environment involves incubation of a polymer substrate with microorganisms or enzymes, only a limited number of measurements are possible:
- 41. 8 Handbook of Biodegradable Polymers, 2nd Edition those pertaining to the substrates, to the microorganisms or to the reaction products. Four common approaches available for studying biodegradation processes have been reviewed in detail by Andrady [13, 14]: • Monitoring the accumulation of biomass. • Monitoring the depletion of substrates. • Monitoring the reaction products. • Monitoring the changes in substrate properties. In the following sections, different test methods for the assessment of polymer biodegradability are presented. Measurements are usually based on one of the four approaches given above, but combinations also occur. Before choosing an assay to simulate environmental effects in an accelerated manner, it is critical to consider the closeness of fit that the assay will provide between substrate, microorganisms or enzymes, and the application or environment in which biodegradation should take place [23]. 1.5.1 Enzyme Assays 1.5.1.1 Principle In enzyme assays, the polymer substrate is added to a buffered or pH-controlled system, containing one or several types of purified enzymes. These assays are very useful in examining the kinetics of depolymerisation, or oligomer or monomer release from a polymer chain under different assay conditions. The method is very rapid (minutes to hours) and can give quantitative information. However, enzyme assays are not suitable to determine mineralisation rates. 1.5.1.2 Applications The type of enzyme to be used, and quantification of degradation, will depend on the polymer being screened. For example, Mochizuki and co-workers [24] studied the effects of the draw ratio of polycaprolactone fibres on enzymatic hydrolysis by lipase. The degradability of polycaprolactone fibres was monitored by dissolved organic carbon (DOC) formation and weight loss. Similar systems with lipases have been used for studying the hydrolysis of broad ranges of aliphatic polyesters [25−30], copolyesters with aromatic segments [26, 31−33] and copolyesteramides [34, 35].
- 42. 9 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers Other enzymes such as α-chymotrypsin and α-trypsin have also been applied to these polymers [36, 37]. The biodegradability of polyvinyl alcohol (PVA) segments, with respect to block length and stereo chemical configuration, has been studied using isolated PVA-dehydrogenase [38]. Cellulolytic enzymes have been used to study the biodegradability of cellulose ester derivatives as a function of the degree of substitution and substituent size [39]. Similar work has been performed with starch esters using amylolytic enzymes such as α-amylases, β-amylases, glucoamylases and amyloglucosidases [40]. Enzymatic methods have also been used to study the biodegradability of starch plastics or packaging materials containing cellulose [41−46]. 1.5.1.3 Drawbacks Caution must be used in extrapolating enzyme assays as a screening tool for different polymers since the enzymes have been paired to only one polymer. The initially selected enzymes may show significantly reduced activity towards modified polymers or different materials, even though more suitable enzymes may exist in the environment. Caution must also be used if the enzymes are not purified or appropriately stabilised or stored, since inhibition and loss of enzyme activity can occur [23]. 1.5.2 Plate Tests 1.5.2.1 Principle Plate tests were initially developed in order to assess the resistance of plastics to microbial degradation. Several methods have been standardised by standardisation organisations such as the ASTM and the ISO [47−49]. They are now also used to see if a polymeric material will support growth [23, 50]. The principle of the method involves placing the test material on the surface of a mineral salts agar in a Petri dish containing no additional carbon source. The test material and agar surface are sprayed with a standardised mixed inoculum of known bacteria and/or fungi. The test material is examined, after a predetermined incubation period at constant temperature, for the amount of growth on its surface and a rating is given. 1.5.2.2 Applications Potts [51] used the method in his screening of 31 commercially available polymers for biodegradability. Other studies, where the growth of either mixed or pure cultures of
- 43. 10 Handbook of Biodegradable Polymers, 2nd Edition microorganisms is taken to be indicative of biodegradation, have been reported [6]. The validity of this type of test and the use of visual assessment alone, for all plastics, has been questioned by Seal and Pantke [52]. They recommended that mechanical properties should be assessed to support visual observations. Microscopic examination of the surface can also give additional information. A variation of the plate test is the ‘clear zone’ technique [53], sometimes used to screen polymers for biodegradability. A fine suspension of polymer is placed in an agar gel as the sole carbon source and the test inoculum is placed in wells bored into the agar. After incubation, a clear zone around the well, detected visually or instrumentally, is indicative of utilisation of the polymer. The method has, for example, been used in the case of starch plastics [54], various polyesters [55−57] and PU [58]. 1.5.2.3 Drawbacks A positive result in an agar plate test indicates that an organism can grow on the substrate, but does not mean that the polymer is biodegradable, since growth may be on contaminants, on plasticisers which are present, on oligomeric fractions still present in the polymer and so on. Therefore, these tests should be treated with caution when extrapolating the data to field situations. 1.5.3 Respiration Tests 1.5.3.1 Principle Aerobic microbial activity is typically characterised by the utilisation of oxygen. Aerobic biodegradation requires oxygen for the oxidation of compounds to its mineral constituents, such as CO2, H2O, sulfur dioxide (SO2), phosphorous pentoxide (P2O5) and so on. The amount of oxygen utilised during incubation, also called the biological oxygen demand (BOD), is therefore a measure of the degree of biodegradation. Several test methods are based on measurement of the BOD, often expressed as a percentage of the theoretical oxygen demand (TOD) of the compound. The TOD, which is the theoretical amount of oxygen necessary for completely oxidising a substrate to its mineral constituents, can be calculated by considering the elemental composition and the stoichiometry of oxidation [13, 59−62] or based on experimental determination of the chemical oxygen demand (COD) [13, 63].
- 44. 11 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers 1.5.3.2 Applications The closed bottle BOD tests were designed to determine the biodegradability of detergents [61, 64]. These have stringent conditions due to the low level of inoculum (in the order of 105 microorganisms/l) and the limited amount of test substance that can be added (normally between 2 and 4 mg/l). These limitations originate from the practical requirement that the oxygen demand should not exceed half the maximum dissolved oxygen level in the water at the temperature of the test, to avoid the generation of anaerobic conditions during incubation. For nonsoluble materials, such as polymers, less stringent conditions are acceptable and alternative ways for measuring BOD were developed. Two-phase (semi) closed bottle tests enable a higher oxygen content in the flasks and permit a higher inoculum level. Higher test concentrations are also possible, encouraging higher accuracy with the direct weighing in of samples. The oxygen demand can alternatively be determined by periodically measuring the oxygen concentration in the aquatic phase by opening the flasks [60, 65−67], by measuring the change in volume or pressure in incubation flasks containing CO2-absorbing agents [59, 68, 69], or by measuring the quantity of oxygen produced (electrolytically) to maintain a constant gas volume/pressure in specialised respirometers [59, 62, 65, 66, 68]. 1.5.3.3 Suitability BOD tests are sensitive and relatively simple to perform, and are therefore often used as screening tests. However, the measurement of oxygen consumption is a nonspecific, indirect measure for biodegradation and is not suitable for determining anaerobic degradation. The requirement for test materials to be the sole carbon/energy source for microorganisms in the incubation media eliminates the use of oxygen measurements in complex natural environments. 1.5.4 Gas (CO2 or CH4) Evolution Tests 1.5.4.1 Principle The evolution of CO2 or CH4 from a substrate represents a direct parameter of mineralisation. Therefore, gas evolution tests can be important tools in the determination of the biodegradability of polymeric materials. A number of well- known test methods have been standardised for aerobic biodegradation, such as the (modified) Sturm test [70−75] and the laboratory controlled composting test [76−79];
- 45. 12 Handbook of Biodegradable Polymers, 2nd Edition as well as for anaerobic biodegradation, such as the anaerobic sludge test [80, 81] and the anaerobic digestion test [82, 83]. Although the principle of these test methods is the same, they may differ in medium composition, inoculum, the way substrates are introduced, and in the technique for measuring gas evolution. 1.5.4.2 Applications Anaerobic tests generally follow biodegradation by measuring the increase in pressure and/or volume due to gas evolution, usually in combination with gas chromatographic analysis of the gas phase [84, 85]. Most aerobic standard tests apply continuous aeration; the exit stream of air can be directly analysed continuously using a CO2 monitor (usually infrared detectors) or titrimetrically after sorption in dilute alkali. The cumulative amount of CO2 generated, expressed as a percentage of the theoretically expected value for total conversion to CO2, is a measure of the extent of mineralisation achieved. A value of 60% carbon conversion to CO2, achieved within 28 days, is generally taken to indicate ready degradability. Taking into account that in this system there will also be incorporation of carbon into the formation of biomass (growth), the 60% value for CO2 implies almost complete degradation. While this criterion is meant for water-soluble substrates, it is probably applicable to very finely divided moderately degradable polymeric materials as well [13]. Nevertheless, most standards for determining the biodegradability of plastics consider a maximum test duration of 6 months. Besides the continuously aerated systems, described above, several static respirometers have been described. Bartha and Pramer [86] describe a two-flask system; one flask, containing a mixture of soil and the substrate, is connected to another chamber holding a quantity of CO2 sorbant. Care must be taken to ensure that enough oxygen is available in the flask for biodegradation. Nevertheless, this experimental set-up and modified versions thereof have been successfully applied in the assessment of the biodegradability of polymer films and food packaging materials [87−89]. The percentage of carbon converted to biomass instead of CO2 depends on the type of polymer and the phase of degradation. Therefore, it has been suggested to regard the complete carbon balance to determine the degree of degradation [90]. This implies that besides the detection of gaseous carbon, the amount of carbon in soluble and solid products also needs to be determined. Soluble products, oligomers of different molecular size, intermediates and proteins secreted from microbial cells can be measured as COD or as DOC. Solid products, biomass, and polymer remnants require a combination of procedures to separate and detect different fractions. The protein content of the insoluble fraction is usually determined to estimate the amount of carbon converted to biomass, using the assumptions that
- 46. 13 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers dry biomass consists of 50% protein and that the carbon content of dry biomass is 50% [90−92]. 1.5.4.3 Suitability Gas evolution tests are popular test methods because they are sensitive and relatively simple to perform. A direct measure for mineralisation is determined and water-soluble or insoluble polymers can be tested as films, powders or objects. Furthermore, the test conditions and inoculum can be adjusted to fit the application or environment in which biodegradation should take place. Aquatic synthetic media is usually used, but also natural seawater [93, 94] or soil samples [86, 88, 89, 95] can be applied as biodegradation environments. A prerequisite for these media is that the background CO2 evolution is limited, which excludes the application of real composting conditions. Biodegradation under composting conditions is therefore measured using an inoculum derived from matured compost with low respiration activity [76−78, 96, 97]. A drawback of using complex degradation environments, such as mature compost, is that the simultaneous characterisation of intermediate degradation products and determination of the carbon balance is difficult due to the presence of a great number of interfering compounds. To overcome this, an alternative test was developed based on an inoculated mineral bed-based matrix [98, 99]. 1.5.5 Radioactively Labelled Polymers 1.5.5.1 Principle and Applications Some materials tend to degrade very slowly under stringent test conditions without an additional source of carbon. However, if readily available sources of carbon are added, it becomes impossible to tell how much of the evolved CO2 can be attributed to decomposition of the plastic. The incorporation of radioactive 14 C in synthetic polymers gives a means of distinguishing between CO2 or CH4 produced via metabolism of the polymer, and that generated by other carbon sources in the test environment. By comparison of the amount of radioactive 14 CO2 or 14 CH4 to the original radioactivity of the labelled polymer, it is possible to determine the percent by weight of carbon in the polymer which was mineralised during the exposure period [51, 100−102]. Collection of radioactively labelled gases or low MW products can also provide extremely sensitive and reproducible methods to assess the degradation of polymers with low susceptibility to enzymes, such as PE [8, 103] and cellulose acetates [104, 105].
- 47. 14 Handbook of Biodegradable Polymers, 2nd Edition 1.5.5.2 Drawbacks Problems with handling the radioactively labelled materials and their disposal are issues on the down side of this method. In addition, in some cases it is difficult to synthesise the target polymer with the radioactive labels in the appropriate locations, with representative MW, or with representative morphological characteristics. 1.5.6 Laboratory-scale Simulated Accelerating Environments 1.5.6.1 Principle Biodegradation of a polymer material is usually associated with changes in the physical, chemical and mechanical properties of the material. It is indeed these changes, rather than the chemical reactions, which make the biodegradation process so interesting from an application point of view. These useful properties might be measured as a function of the duration of exposure to a biotic medium, to follow the consequences of the biodegradation process on material properties. Biotic media can be specifically designed at laboratory scale to mimic natural systems whilst allowing maximum control of variables such as temperature, pH, microbial community, mechanical agitation and supply of oxygen. Regulating these variables improves the reproducibility and may accelerate the degradation process. Laboratory simulations can also be used for the assessment of long-term effects, achieved by continuous dosing, on the activity and environment of the disposal system [50]. 1.5.6.2 Applications The Organisation for Economic Co-operation and Development’s ‘Coupled Unit’ test [106] simulates an activated sludge sewage treatment system, but its application for polymers would be difficult as DOC is the parameter used to assess biodegradability. Krupp and Jewell [107] described well-controlled anaerobic and aerobic aquatic bioreactors to study the degradation of a range of commercially available polymer films. A relatively low loading rate of the semicontinuous reactors and a long retention time were maintained to maximise the biodegradation efficiency. Experimental set-ups have also been designed to simulate marine environments [108], soil burial conditions [108−110], composting environments [111−116], and landfill conditions [117−119] at laboratory scale, with controlled parameters such as temperature and moisture level, and a synthetic waste to provide a standardised basis for comparing the degradation kinetics of films.
- 48. 15 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers A wide choice of material properties can be followed during the degradation process. However, it is important to select one which is relevant to the end-use of the polymer material or provides fundamental information about the degradation process. Weight loss is a parameter frequently followed because it clearly demonstrates the disintegration of a biodegradable product [120−122]. Tensile properties are also often monitored, due to interest in the use of biodegradable plastics in packaging applications [54, 123, 124]. In those polymers where biodegradation involves a random scission of the macromolecular chains, a decrease in the average MW and a general broadening of the MW distribution provide initial evidence of a breakdown process [86, 125, 126]. However, no significant changes in material characteristics may be observed in recovered material if the mechanism of biodegradation involves bioerosion, i.e., enzymatic or hydrolytic cleavage at the surface. Visual examination of the surface with various microscopic techniques can also give information on the biodegradation process [115, 127−130]. Likewise, chemical and/or physical changes in the polymer may be followed by (combinations of) specific techniques such as infrared [10, 131] or ultraviolet (UV) spectroscopy [84, 132], nuclear magnetic resonance measurements [115, 126−133], X-ray diffractometry [115, 134, 135] and differential scanning calorimetry (DSC) [115, 136, 137]. 1.5.6.3 Drawbacks An inherent drawback in the use of mechanical properties, weight loss, MW, or any other property which relies on the macromolecular nature of the substrate is that in spite of their sensitivity, these can only address the early stages of the biodegradation process. Furthermore, these parameters give no information on the extent of mineralisation. Especially in material blends or copolymers, the hydrolysis of one component can cause significant disintegration (and thus loss of weight and tensile properties) whereas other components may persist in the environment, even in a disintegrated form [13]. Blends of starch, poly(3-hydroxy butyrate) or poly(ε- caprolactone) with polyolefins are examples of such systems [11, 43, 138]. 1.5.7 Natural Environments, Field Trials Exposure in natural environments provides the best true measure of the environmental fate of a polymer, because these tests include a diversity of organisms and achieve a desirable natural closeness of fit between the substrate, microbial agent and the environment. However, the results of that particular exposure are only relevant to the specific environment studied, which is likely to differ substantially from many other environments. An additional problem is the timescale for this method, since the degradation process, depending on the environment, may be very slow (months
- 49. 16 Handbook of Biodegradable Polymers, 2nd Edition to years) [23]. Moreover, little information on the degradation process can be gained other than the real time required for weight loss or total disintegration. Nevertheless, field trials in natural environments are still used to extrapolate results acquired in laboratory tests to biodegradation behaviour under realistic outdoor conditions [115, 116, 127, 139, 140]. 1.6 Conclusions The overview presented above makes clear that there is no such thing as a single optimal method for determining the biodegradation of polymeric materials. First of all, the biodegradation of a material is not only determined by the chemical composition and corresponding physical properties, but the degradation environment, to which the material is exposed, also affects the rate and degree of biodegradation. Furthermore, the method or test to be used depends on what information is requested; especially as the biodegradation concept is very important in relation to the end of life of a material, while it could be just one aspect of health and environmental safety in other cases. It is fairly obvious, but often neglected, that one should always consider why a particular polymeric material should be (or not be) biodegradable when contemplating how to assess its biodegradability. After all, it is the intended application of the material that governs the most suitable testing environment, the parameters to be measured during exposure and the corresponding limit values. For example, investigating whether biodegradation of a plastic material designed for food packaging could facilitate undesired growth of (pathogenic) microorganisms requires a completely different approach from investigating whether its waste can be discarded via composting (i.e., whether it degrades sufficiently rapidly to be compatible with existing biowaste composting facilities). It is important to state that it will not be sufficient to ascertain macroscopic changes, such as weight loss and disintegration, or growth of microorganisms, to define a material as biodegradable because these observations may originate from a partial biodegradation or from the degradation of a component of the material itself. In order to study the real biodegradation of a material in the environment (composting, anaerobic digestion, soil and water) it is necessary to determine the mineralisation, which is the transformation of the material into: CO2, CH4 (anaerobic condition), water and new biomass. Furthermore, it is important to evaluate the eventual toxic effects that the addition of the material could have on the environment, in order to avoid introducing dangerous substances. In this way we will be sure that no harm will be caused to the environment itself. This is the same approach followed by the principal standardisation bodies with standards regarding the compostability of plastics and packaging. These standards
- 50. 17 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers (European Norms 13432, ISO 17088 and ASTM D6400) describe the specifications for compostable plastics and packaging. References 1. T. Hayashi, Progress in Polymer Science, 1994, 19, 663. 2. D.F. Williams and S.P. Zhong, International Biodeterioration Biodegradation, 1994, 34, 95. 3. F. Buchanan in Degradation Rate of Bioresorbable Materials – Prediction and Evaluation, Woodhead Publishing Ltd, Cambridge, UK, 2008. 4. A. Göpferich, Biomaterials, 1996, 17, 103. 5. G. Mabilleau and A. Sabokbar in Degradation Rate of Bioresorbable Materials – Prediction and Evaluation, Ed., F. Buchanan, Woodhead Publishing Ltd, Cambridge, UK, 2008, p.145. 6. A‑C. Albertsson and S. Karlsson in Degradable Materials − Perspectives, Issues and Opportunities, Eds., S.A. Barenberg, J.L. Brash, R. Narayan and A.E. Redpath, CRC Press, Boston, MA, USA, 1990. 7. A.C. Palmisano and C.A. Pettigrew, Bioscience, 1992, 42, 680. 8. A-C. Albertsson and B. Rånby, Journal of Applied Polymer Science: Applied Polymer Symposium, 1979, 35, 423. 9. R.G. Austin in Degradable Materials − Perspectives, Issues and Opportunities, Eds., S.A. Barenberg, J.L. Brash, R. Narayan and A.E. Redpath, CRC Press, Boston, MA, USA, 1990, p.209. 10. S.M. Goheen and R.P. Wool, Journal of Applied Polymer Science, 1991, 42, 2691. 11. V.T. Breslin, Journal of Environmental Polymer Degradation, 1993, 1, 127. 12. Anonymous in Towards Common Ground − Meeting Summary of the International Workshop on Biodegradability, Annapolis, Maryland, USA, 20−21st October, 1992. 13. A.L. Andrady, Journal of Macromolecular Science: Reviews in Macromolecular Chemistry Physics, 1994, C34, 25.
- 51. 18 Handbook of Biodegradable Polymers, 2nd Edition 14. A.L. Andrady in Handbook of Polymer Degradation, 2nd Edition, Ed., S.H. Hamid, Marcel Dekker Inc., New York, NY, USA, 2000, p.441. 15. T. St.Pierre and E. Chiellini, Journal of Bioactive and Compatible Polymers, 1986, 1, 467. 16. T. St.Pierre and E. Chiellini, Journal of Bioactive and Compatible Polymers, 1987, 2, 4. 17. R.E. Cameron and A. Kamvari-Moghaddam in Degradation Rate of Bioresorbable Materials – Prediction and Evaluation, Ed., F. Buchanan, Woodhead Publishing Ltd, Cambridge, UK, 2008, p.43. 18. L. Stryer in Biochemistry, 2nd Edition, W.H. Freeman and Company, New York, NY, USA, 1981. 19. T.A. Anderson, R. Tsao and J.R. Coats, Journal of Environmental Polymer Degradation, 1993, 1, 301. 20. P.J. Whitney, C.H. Swaffield and A.J. Graffam, International Biodeterioration and Biodegradation, 1993, 31, 179. 21. M. Van der Zee, J.H. Stoutjesdijk, P.A.A.W. Van der Heijden and D. De Wit, Journal of Environmental Polymer Degradation, 1995, 3, 235. 22. G. Eggink, M. Van der Zee and L. Sijtsma in International Edition of the IOP on Environmental Biotechnology, IOP-Milieubiotechnologie, The Hague, The Netherlands, 1995, p.7. 23. J.M. Mayer and D.L. Kaplan in Biodegradable Polymers and Packaging, Eds., C. Ching, D.L. Kaplan and E.L. Thomas, Technomic Publishing Co. Inc., Lancaster, PA, USA, 1993, p.233. 24. M. Mochizuki, M. Hirano, Y. Kanmuri, K. Kudo and Y. Tokiwa, Journal of Applied Polymer Science, 1995, 55, 289. 25. Y. Tokiwa and T. Suzuki, Journal of Applied Polymer Science, 1981, 26, 441. 26. Y. Tokiwa, T. Suzuki and K. Takeda, Agricultural and Biological Chemistry, 1986, 50, 1323. 27. I. Arvanitoyannis, A. Nakayama, N. Kawasaki and N. Yamamoto, Polymer, 1995, 36, 2271.
- 52. 19 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers 28. A. Nakayama, N. Kawasaki, I. Arvanitoyannis, J. Iyoda and N. Yamamoto, Polymer, 1995, 36, 1295. 29. T. Walter, J. Augusta, R-J. Müller, H. Widdecke and J. Klein, Enzyme and Microbial Technology, 1995, 17, 218. 30. M. Nagata, T. Kiyotsukuri, H. Ibuki, N. Tsutsumi and W. Sakai, Reactive and Functional Polymers, 1996, 30, 165. 31. H.S. Jun, B.O. Kim, Y.C. Kim, H.N. Chang and S.I. Woo, Journal of Environmental Polymer Degradation, 1994, 2, 9. 32. E. Chiellini, A. Corti, A. Giovannini, P. Narducci, A.M. Paparella and R. Solaro, Journal of Environmental Polymer Degradation, 1996, 4, 37. 33. M. Nagata, T. Kiyotsukuri, S. Minami, N. Tsutsumi and W. Sakai, Polymer International, 1996, 39, 83. 34. M. Nagata and T. Kiyotsukuri, European Polymer Journal, 1994, 30, 1277. 35. M. Nagata, Macromolecular Rapid Communications, 1996, 17, 583. 36. I. Arvanitoyannis, E. Nikolaou and N. Yamamoto, Polymer, 1994, 35, 4678. 37. I. Arvanitoyannis, E. Nikolaou and N. Yamamoto, Macromolecular Chemistry and Physics, 1995, 196, 1129. 38. S. Matsumura, Y. Shimura, K. Toshima, M. Tsuji and T. Hatanaka, Macromolecular Chemistry and Physics, 1995, 196, 3437. 39. W.G. Glasser, B.K. McCartney and G. Samaranayake, Biotechnology Progress, 1994, 10, 214. 40. C. Rivard, L. Moens, K. Roberts, J. Brigham and S. Kelley, Enzyme and Microbial Technology, 1995, 17, 848. 41. A.A. Strantz and E.A. Zottola, Journal of Food Protection, 1992, 55, 736. 42. V. Coma, Y. Couturier, B. Pascat, G. Bureau, J.L. Cuq and S. Guilbert, Enzyme and Microbial Technology, 1995, 17, 524. 43. S.H. Imam, S.H. Gordon, A. Burgess‑Cassler and R.V. Greene, Journal of Environmental Polymer Degradation, 1995, 3, 107.
- 53. 20 Handbook of Biodegradable Polymers, 2nd Edition 44. S.H. Imam, S.H. Gordon, R.L. Shogren and R.V. Greene, Journal of Environmental Polymer Degradation, 1995, 3, 205. 45. M. Vikman, M. Itävaara and K. Poutanen, Journal of Macromolecular Science, Part A: Pure and Applied Chemistry, 1995, A32, 863. 46. M. Vikman, M. Itävaara and K. Poutanen, Journal of Environmental Polymer Degradation, 1995, 3, 23. 47. ASTM G21-09, Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi, American Society for Testing and Materials, Philadelphia, PA, USA, 2009. 48. ASTM G22-76, Standard Practice for Determining Resistance of Plastics to Bacteria, American Society for Testing and Materials, Philadelphia, PA, USA, 1996. {Withdrawn in 2002} 49. ISO 846:1997, Plastics – Evaluation of the Action of Microorganisms, International Organization for Standardization, Genève, Switzerland, 1997. 50. K.J. Seal in Chemistry and Technology of Biodegradable Polymers, Ed., G.J.L. Griffin, Blackie Academic and Professional, London, UK, 1994, p.116. 51. J.E. Potts in Aspects of Degradation and Stabilization of Polymers, Ed., H.H.G. Jellinek, Elsevier Scientific Publishing Co., Amsterdam, The Netherlands, 1978, p.617. 52. K.J. Seal and M. Pantke, Material und Organismen, 1986, 21, 151. 53. F.P. Delafield, M. Doudoroff, N.J. Palleroni, C.J. Lusty and R. Contopoulos, Journal of Bacteriology, 1965, 90, 1455. 54. J.M. Gould, S.H. Gordon, L.B. Dexter and C.L. Swanson in Agricultural and Synthetic Polymers − Biodegradability and Utilization, Eds., J.E. Glass and G. Swift, ACS Symposium Series 433, American Chemical Society, Washington, DC, USA, 1990, p.65. 55. J. Augusta, R-J. Müller and H. Widdecke, Applied Microbiology and Biotechnology, 1993, 39, 673. 56. H. Nishida and Y. Tokiwa, Chemistry Letters, 1994, 3, 421. 57. H. Nishida and Y. Tokiwa, Chemistry Letters, 1994, 7, 1293.
- 54. 21 Methods for Evaluating the Biodegradability of Environmentally Degradable Polymers 58. J.R. Crabbe, J.R. Campbell, L. Thompson, S.L. Walz and W.W. Schultz, International Biodeterioration and Biodegradation, 1994, 33, 103. 59. ISO 9408:1999(E), Water Quality − Evaluation of Ultimate Aerobic Biodegradability of Organic Compounds in Aqueous Medium by Determination of Oxygen Demand in a Closed Respirometer, International Organization for Standardization, Genève, Switzerland, 1999. 60. ISO 10708:1997(E), Water Quality − Evaluation in an Aqueous Medium of the Ultimate Aerobic Biodegradability of Organic Compounds − Determination of Biochemical Oxygen Demand in a Two-phase Closed Bottle Test, International Organization for Standardization, Genève, Switzerland, 1997. 61. OECD 301D, Ready Biodegradability: Closed Bottle Test, Guidelines for Testing of Chemicals, Organisation for Economic Co-operation and Development, Paris, France, 1992. 62. OECD 302C, Inherent Biodegradability: Modified MITI Test (II), Guidelines for Testing of Chemicals, Organisation for Economic Co-operation and Development, Paris, France, 2009. 63. ISO 6060:1989(E), Water Quality – Determination of the Chemical Oxygen Demand, International Organization for Standardization, Genève, Switzerland, 1989. 64. ISO 10707:1997(E), Water Quality − Evaluation in an Aqueous Medium of the ‘Ultimate’ Aerobic Biodegradability of Organic Compounds − Method by Analysis of Biochemical Oxygen Demand (Closed Bottle Test), International Organization for Standardization, Genève, Switzerland, 1997. 65. ISO 14851:2004(E), Determination of the Ultimate Aerobic Biodegradability of Plastic Materials in an Aqueous Medium − Method by Determining the Oxygen Demand in a Closed Respirometer, International Organization for Standardization, Genève, Switzerland, 2004. 66. ASTM D5271-02, Standard Test Method for Determining the Aerobic Biodegradation of Plastic Materials in an Activated-Sludge-Wastewater- Treatment System, American Society for Testing and Materials, Philadelphia, PA, USA, 2002. {Withdrawn in 2011}
- 55. Random documents with unrelated content Scribd suggests to you:
- 56. made a report of their investigations to the government, and later in the same year an act of the Provincial Legislature was passed, renewed and amended in 1850. It authorized the lieutenant- governor to establish a health committee. This committee recommended the erection of a lazaretto on l’Ile de Sheldrake, an isolated spot in the middle of the Miramichi River eighteen miles above Chatham. “Whoever was found to be unquestionably tainted by the disease,” says the article, “must be torn from his family, using force if needful. The husband must be taken from his wife, the mother from her children, the child from its parents, whenever the first symptom of leprosy declares itself. An eternal farewell to all they hold most dear must be said, and the poor creature is sent to the lazaretto. It often happens that a leper refuses to go quietly; he is then dragged by ropes like a beast to the shambles—for none is willing to lay a finger upon him. Often the unhappy beings are driven with blows to the very door of the lazaretto.” Things, of course, could not long remain in this brutal condition. The lepers, driven to desperation by their physical and mental sufferings, by a wild longing for the liberty denied them, and for the sight of their loved ones, sometimes effected their escape. An attempt was finally made to ameliorate their condition, and in 1847 the lazaretto was removed to the spot where it now stands, about half a mile from the parish church of Tracadie. A large tract of land was here purchased by the government, and the present building was erected, surrounded by a wooden wall twenty feet high, set thick with nails to hinder the escape of the lepers. The windows of the lazaretto were barred heavily with iron, and thus added to the melancholy aspect of the building. The lepers, weary of the revolting resemblance to a prison, themselves tore most of the bars away, and, when the nuns arrived there they at once ordered the remainder to be removed. In 1868 the nuns from the Hôtel Dieu of Montreal took possession of the lazaretto of Tracadie. For some few years a strong necessity had been felt for the reorganization of this institution. A wish was expressed that it could be placed under the care of the Hospital
- 57. Nuns. I have now before me a letter from the Rt. Rev. James Rogers, Bishop of Chatham, in which is given an account, for the Conseil Central de la Propagation de la Foi at Paris, of the steps that had been taken up to December, 1866: “Since my first visit to the establishment,” says the bishop, “I have always thought that it would be most desirable to place it under the care of the Sisters of the Hôtel Dieu, who would watch over the souls and the bodies of these sufferers, whose number varies from twenty to thirty. But so many great and pressing needs claimed my attention—while my resources were insufficient even for the alleviation of physical suffering, and also, perhaps, for the spiritual wants of certain souls—I was compelled to postpone my plans in regard to the lazaretto, until my diocese could satisfy the religious needs of its inhabitants by an increase of the number of priests, and by the erection of chapels in places where they had long and earnestly been demanded, and also by the establishment of schools for the Christian education of youth. Another obstacle to the immediate execution of my intention was the lukewarm approbation and co- operation of the government. The total lack of suitable lodging for the nuns, as well as the uncertainty whether the Protestant element which pervades our government and our legislature would be willing to grant us funds or permit us to make needful preparations for the sisters to take charge of the lazaretto—all conspired as hindrances to my desires. “Last spring I petitioned the government, but political changes interfered, and no steps were taken until now. This is the reason why the worthy curé of Tracadie continues to be the only priest who administers the consolations of religion to that portion of his flock so bitterly afflicted.” The steps taken by Bishop Rogers seem to have been singularly felicitous. He obtained from Bishop Bourget the assistance of the nuns of the Hôtel Dieu of Montreal, and the government appears to
- 58. have regarded with favorable eyes this regeneration of the lazaretto, which produced in a very brief period of time the best possible results upon the patients. Abbé Gauvreau draws a sad picture of the state in which these poor creatures lived before the nuns went to their assistance. In a letter dated April 28, 1869, addressed to the mother-superior of the Hôtel Dieu of Montreal, he says: “I am absolutely incapable of describing the state of abject misery in which our poor lepers passed their lives before the coming of the sisters. I can only say that from the hour of their transfer from l’Ile aux Bec-scies (Sheldrake) at the entrance of the river Miramichi, discord, revolt, and insubordination toward the government, divisions and quarrels among themselves, made the history of their daily lives. The walls rang with horrible blasphemies, and the hospital seemed like a den of thieves.” The Board of Health spared nothing to make the lepers comfortable. Good food, and abundance of it, appropriate clothing, and careful medical attendance were liberally provided; but, in spite of these efforts, the hearts of these poor creatures were as diseased as their bodies. Some of them revolted against the summons of death, notwithstanding the constant exhortations of the chaplain, and even after their last communion clung strongly to the futile hope of life. Of this number was one who had been warned by the physician that his hours were numbered and that a priest should be summoned. His friends, and those of his relatives who were within the walls of the lazaretto, implored him to prepare for death. “Let me be!” he cried. “I know what I am about!” About nine o’clock in the evening he begged his companions in misery not to watch at his bedside, and, believing himself able to drive away Death, who was hurrying toward him with rapid strides, insisted on playing a game of cards. The game had hardly begun, however, when the cards dropped from his hands and he fell back on his bed. Before assistance could reach him all was over.
- 59. With the arrival of the nuns a new order of things began. Without entering into a detailed account of all the labors performed by the sisters since their arrival, it is enough to state that cleanliness and order prevail and true charity shows itself everywhere. The poor creatures, who formerly revelled in filth and disorder, now see about them decency and cleanliness. They are induced to be submissive and obedient by the hourly example of the sisters; their modesty and reserve, their virtue and careful speech, their watchful care and devotion, their tender attention to the sick, teach the inmates of the hospital the best of lessons. It is easy to imagine with what joy the poor lepers welcomed the nuns who came to consecrate their lives to this service, and also to understand with what affection and respect these holy women are regarded. “The enclosed grounds of the lazaretto,” says Governor Gordon in his Wilderness Journeys, “consist of a green meadow three or four acres in extent. Within these limits the lepers are permitted to wander at their will. Until recently they were confined to the narrowest limits—a mere yard about the lazaretto. I entered these dreary walls, accompanied by the Roman Catholic Bishop of Chatham, by the secretary of the Board of Health, by the resident physician, and by the Catholic priest of the village, who is also the chaplain of the institution. “Within the enclosure are several small wooden buildings, separated from each other, consisting of the kitchen, laundry, etc. A bath-house has recently been added to these, which will be a source of infinite comfort to the patients. The hospital contains two larger halls—one devoted to the men, the other to the women. Each room has a stove and a table with chairs about it, while the beds are ranged against the wall. These halls are both well lighted and ventilated, and at the time of my inspection were perfectly clean and fresh. At the end of these halls is a small chapel arranged in such a way that the patients of both sexes are able to hear Mass without meeting each other.
- 60. Through certain openings they also confess to the priest and receive the holy communion.” Many changes in the interior arrangements of the lazaretto followed the arrival of the sisters. The patients and the nuns now hear Mass at the same time. The male patients occupy two rooms twenty-five feet square, while similar apartments above are reserved for the females. The grounds of the lazaretto have also been enlarged. “Before giving the characteristics of this appalling disease,” says Mr. Gordon, “I wish to reply to a question which you undoubtedly wish to ask: How is this malady propagated? No one knows. It seems not to be hereditary, since in one family the father or mother may be attacked, while the children entirely escape. In others the children are leprous and the parents healthy. In 1856 or '57 a woman named Domitile Brideau, wife of François Robichaud, was so covered with leprosy that her body was one mass of corruption. While in this state she gave birth to a daughter, whom she nursed—the mother shortly afterward dying in the hospital. Meanwhile, the child was absolutely healthy, and remained until she was three years of age in the hospital without any unfavorable symptoms being developed. The girl grew to womanhood and married, and to-day she and her children are perfectly healthy. Many similar examples might be cited.” This malady, then, can hardly be contagious, since in one family husband or wife may be attacked, while the other goes unscathed. There is now at Tracadie a man, François Robichaud by name, who has had three wives; the two first perished of leprosy, the third is now under treatment at the lazaretto—the husband in the meanwhile enjoying perfect health. In one family two or more children are lepers, while the others are untainted. One servant- woman resided for eight years in the hospital, ate and drank with the patients, yet has never shown any symptoms of the disease. The laundress of the institution lives under its roof, and has done so for two years; she is a widow, her husband having died of the scourge,
- 61. she being his sole nurse during his illness. She is in perfect health. It has also happened more than once that persons suspected of leprosy, and placed in the hospital, after remaining there several years and developing no further symptoms, are discharged as “whole.” All the patients now in the hospital agree that the disease is communicated by touch, and each has his own theory as to where he was exposed to it—either by sleeping with some one who had it, or by eating and drinking with such. I am strongly persuaded that this disease, whatever may be its origin, is greatly aggravated by the kind of life led by the natives of Tracadie, who are all fishermen or sailors. Their food is fish, generally herring, and their only vegetables turnips and potatoes. Such is their extreme poverty that there are not ten families in Tracadie who ever touch bread. Let us follow Governor Gordon into the lazaretto. “At the time of my visit,” he says, “there were twenty-three patients, thirteen men and ten women. They were all French and all Catholics, belonging to the lower class. They were of all ages, and had reached various stages of the disease. One old man, whose features were distorted out of all semblance to humanity, and who had apparently entered his second childhood, could hardly be sufficiently aroused from his apathy to receive the benediction of the bishop, before whom all the others sank on their knees. “There were also young people who, to a casual observer, seemed vigorous and in health; while, saddest of all sights was that of the young children condemned to spend their lives in this terrible place. Above all was I touched by the sight of three small boys from eleven to fifteen years of age. To an inexperienced observer they had much the look of other children of their own age and class. Their eyes were bright and intelligent, but the fatal symptoms that had sufficed to separate them from home
- 62. and kindred were written on their persons, and they were immured for life in the lazaretto. “The greatest sympathy must naturally be felt for these younger victims when one thinks of the possible length of years that stretches before them, hopeless and cheerless; to grow to manhood with the capacities, passions, and desires of manhood, and condemned to live from youth to middle age, from middle age to decrepitude possibly, with no other society than that of their companions in misery. Utterly without occupations, amusements, or interests, shut off from all outside resources, their only excitement is found in the arrival of a new disease- stricken patient, their only occupation that of watching their companions dying before their eyes by inches! “But few of the patients could read, and those who could were without books. There was evident need of some organization that might furnish the patients with employment. Both mind and body required occupation. Under these circumstances I was by no means surprised to learn that in the last stages of the disease the mind was generally much weakened. “The suffering of the majority of the patients was by no means severe, and I was informed that one of the characteristic features of the malady was profound insensibility to pain. One individual was pointed out to me, who by mistake had laid his arm and open hand on a red-hot stove, and who knew nothing of it until the odor of burning flesh aroused his attention.” After Governor Gordon’s visit the condition of the lepers was much improved. The sisters taught the young to read and employed them in making shoes and other articles. The investigations of Governor Gordon, although made during a brief inspection of the lazaretto, are correct as far as they go, but are far from complete. The Abbé Gauvreau has been for eighteen years chaplain of the hospital. He has watched keenly the progress of the disease in over a hundred cases. He has noted every symptom of its
- 63. slow and fatal march. He has been present at the deathbeds of many of the lepers, and he recounts with horror the terrible scenes he has witnessed. “Without wishing to impose my opinions on you,” he says, “I cannot resist the conviction that, apart from divine will, this scourge of fallen man is a most subtle poison introduced into the human body by transmission or by direct contact, or even, perhaps, by prolonged cohabitation. “But whichever of these suppositions is the more nearly correct, when once the poison is fairly within the system its action is so latent and insidious that for some years—two, four, or even more —the unfortunate Naaman or Giezi perceives in himself no change either in constitution or sensations. His sleep is as refreshing and his respiration as free as before. In a word, the vital organs perform all their functions and the various members are unshorn of their vigor and energy. “At this period of the disease the skin loses its natural color, its healthy appearance, and is replaced by a deadly whiteness from head to foot. This whiteness looks as if the malady had taken possession of the mucous membrane and had displaced the fluids necessary to its functions. Without knowing if the leper of the Orient possesses other external indications, it is certain that in this stage the malady of Tracadie is precisely similar to the leprosy of the ancients—I mean in the whiteness of the skin. In the second stage the skin becomes yellow. In the third and last it turns to a deep red; it is often purple, and sometimes greenish, in hue. In fact, the people of Tracadie, like myself, are so familiar with the early symptoms of the disease that they rarely fall into a mistake. “Only one death has ever occurred in the first stage—that of Cyrille Austin. All the other cases have passed on to the second or third stages before death; and, strangely enough, it has been remarked by the patients themselves that the treatment of Dr. La
- 64. Bellois had always a much better chance of success during the third period than during the second. “At first the victim feels devouring thirst, great feverish action, and a singular trembling in every limb; stiffness and a certain weakness in the joints; a great weight on the chest like that caused by sorrow; a rush of blood to the brain; fatigue and drowsiness, and other disagreeable symptoms which now escape my memory. The entire nervous system is then struck, as it were, with insensibility to such a degree that a sharp instrument or a needle, or even the blade of a knife, buried in the fleshy parts or thrust through the tendons and cartilage, causes the leper little or no pain. Some poor creature, with calm indifference, will place his arm or leg on a mass of burning wood and tar, and let it remain there until the entire limb, bones and all, is consumed; yet the leper feels no pain, and may sleep through it all as quietly as if in his bed.” In another letter the abbé gives the following example of this astonishing insensibility: “One of these afflicted beings who died at the lazaretto, and to whom I administered the last sacraments, lay down to sleep near a hot fire; in his slumbers he thrust one arm and hand into the flames, but continued to sleep. The overpowering smell of burning flesh awakened one of his companions, who succeeded in saving his life.” One of the nuns says: “Since we reached Tracadie two of the patients have burned their hands severely, and were totally unconscious of having done so until I dressed the wounds myself.” In regard to this torpidity of the system, M. Gauvreau remarks that it is but temporary, but he knows not its duration; and the nun adds that the torpidity is not invariable with all the patients, and with some only in a portion of the body. In certain individuals it is only in the legs; in others, in the hands alone; but all complain of numbness like that of paralysis.
- 65. “By degrees,” says M. Gauvreau, “the unnatural whiteness of the skin disappears, and spots of a light yellow are to be seen. These spots in some cases are small and about the size of a dollar-piece. When of this character, they appear at first with a certain regularity of arrangement, and in places corresponding with each other, as on the two arms and shoulders—more generally, however, on the breast. They are distinct, but by degrees the poison makes its way throughout the vitals; the spots enlarge, approach each other, and, when at last united, the body of the sick man becomes a mass of corruption. Then the limbs swell, afterward portions of the body, the hands, and the feet; and when the skin can bear no further tension it breaks, and running sores cover the patient, who is repulsive and disgusting to the last degree. “The entire skin of the body becomes extremely tender, and is covered with an oily substance that exudes from the pores and looks like varnish. The skin and flesh between the thumb and forefinger dry away, the ends of the fingers, the feet, and hands dwindle to nothingness, and sometimes the joints separate, and the members drop off without pain and often without the knowledge of the patient. “The most noble part of the being created in the image of God— the face—is marred as much as the body by this fell disease. It is generally excessively swollen. The chin, cheeks, and ears are usually covered by tubercles the size of peas. The eyes seem to start from their sockets, and are glazed by a sort of cataract that often produces complete blindness. The skin of the forehead thickens and swells, acquiring a leaden hue, which sometimes extends over the entire countenance, while in other cases the whole face is suffused with scarlet. The explanation of these different symptoms may be found, of course, in the variety of temperaments—sanguine, bilious, or lymphatic. This face, once so smooth and fair, has become seamed and furrowed. The lips are two appalling ulcers—the upper lip much swollen and raised to the base of the nose, which has entirely disappeared; while
- 66. the under lip hangs over the chin, which shines from the tension of the skin. Can a more frightful sight be imagined? In some cases the lips are parched and drawn up like a purse puckered on strings. This deformity is the more to be regretted is it precludes the afflicted from participation in the holy communion. Leprosy—that of Tracadie, at least—completes its ravages on the internal organs of its victims. It attacks now the larynx and all the bronchial ramifications; they become obstructed and filled with tubercles, so that the unhappy patient can find no relief in any position. His respiration becomes gradually more and more impeded, until he is threatened with suffocation. I have been present at the last struggles of most of these afflicted mortals. I hope that I may never be called upon to witness similar scenes. Excuse me from the details. If I undertook them my courage would give out; for I assure you that many of you would have fainted. Let me simply add that these lepers generally die in convulsions, panting for air; frequently rushing to the door to breathe; and, returning, they fling themselves on their pallets in despair. The thought of their sighs and sobs, the remembrance of their tears, almost breaks my heart, and their prayers for succor ring constantly in my ears: 'O my God! have mercy on me! have mercy on me!’ “At last comes the supreme moment of this lingering torture, and the patient dies of exhaustion and suffocation. All is over, and another Lazarus lies in Abraham’s bosom!” After the above vivid picture of this loathsome disease we naturally ask if the evil be such that no medical skill can combat it with success. The Hospital Nun in the infirmary of the lazaretto tells us all that she has yet learned upon this point. In 1849 and 1850 Dr. La Bellois, a celebrated French physician residing at Dalhousie, treated the lepers for six months and claimed to have cured ten of them: T. Goutheau, Charles Comeau, T. Brideau, A. Benoit, L. Sonier, Ed. Vienneau, Mme. A. Sonier, M. Sonier, Mme. Ferguson, Melina Lavoie. “All the above cases are now
- 67. quite well, and the treatment I adopted was entirely for syphilitic disease, thus establishing without any doubt the nature of the disease” (extract from La Bellois’ report, Feb. 12, 1850). Meanwhile, from the report of the secretary of the Board of Health— Mr. James Davidson—we gather that all the sick above mentioned returned after a time to the hospital; that they died there, with the exception of three, of whom two died in their own houses and the third still lives. Of this one Dr. Gordon, of Bathurst, says: “The disease is slow in its progress, but it is sure, and the fatal termination cannot be far off.” Dr. Nicholson undertook the treatment at the lazaretto. By a certain course of medicine, the details of which he kept a profound secret, and with the aid of vapors, he wonderfully improved the physical condition of the lepers, who in many instances indulged sanguine hopes of recovery. Unfortunately, however, this physician suddenly abandoned his profession, and, to the sorrow of his former patients, died three years later. The lepers soon relapsed into their former hopeless state, and since then no change has taken place. “On our arrival at Tracadie,” said the sister, “we found twenty inmates of the hospital, and since three more have been admitted. These poor creatures, being firmly persuaded that we could cure them, besieged us with entreaties for medicine, and were satisfied with whatever we gave. At first I selected three who had undergone no medical treatment; these three were also the only ones who suffered from contraction of the extremities. The first, twenty-two years of age, had been at the hospital four years, and as yet showed the disease only in the contraction above mentioned, and in a certain insensibility of the feet and hands. The second, fifteen years old, had been in the hospital for two years, his hands and feet were drawn up, and he suffered from a large swelling on the left foot. This young fellow is very delicate, and suffers intensely at times from spasms of the stomach. The third case is a lad of eleven, who for two years has suffered from the disease. His hands are twisted out of
- 68. shape, and his body is covered with spots, red and white; these spots are totally without sensibility. I have administered to these patients the remedies as prescribed by Mr. Fowle—Fowle’s Humor Cure, an American patent medicine. The first and second patient experienced no other benefit from this remedy than a certain vigor previously unfelt. To the third the sensibility of the cuticle returned, but the spots remained the same. This in itself is very remarkable, because in no previous case have these benumbed or paralyzed parts regained their sensation. To another, a patient of twenty-two, I gave the same remedy. For eight years he had been a martyr to the virulence of the disease. When we arrived at the lazaretto, we found his case to be one of the worst there. His nose had fallen in; the lips were enormously puffed and swollen; his hands equally so, and looked more like the paws of a bear than like the hands of a human being. The saliva was profuse, but the effort of swallowing almost futile. Soon after taking this same medicine the saliva ceased to flow and he swallowed with comparative ease. “On the 23d of January he was, by the mercy of God, able to partake of the holy communion, of which he had been deprived for four years. His lips are now of their natural size, and he is stronger than he has been for years. But the pains in his limbs are far worse than they have ever before been. I have also given Fowle’s cure to all the patients who had been under no previous medical treatment, and invariably with beneficial results. In some the tint of the skin is more natural; in others the swelling of the extremities is much abated; but the remedy seems always to occasion an increase of pains in the limbs, although it unquestionably acts as a tonic upon the poor creatures. In all of them the mouth and throat improve with the use of Fowle’s cure. And here let me say that this disease throughout bears a strong resemblance to syphilis. In both diseases the throat, the tongue, and the whole inside of the mouth are ulcerated. In both diseases the voice is affected to such a degree that it can hardly make itself heard. They cough frightfully, and some time after
- 69. our coming a leper presented himself for admission at our hospital doors. The poor creature was covered with ulcers and every night was bathed in a cold perspiration. After he had rested for a few days, I gave him a powerful dose of la liqueur arsenicale, which has since been repeated. The night-sweats have disappeared, and the ulcers are healed, with the exception of one on the foot. His lips are still unhealthy, but he is much stronger, and the spots on his person are gradually disappearing. “Two others, later arrivals have taken la liqueur arsenicale and have improved under its use. Suspecting that the origin of this malady may be traced to another source, and remembering the opinion of Dr. La Bellois, I gave the bichloride of mercury, in doses of the thirty-second part of a grain, to the worst case in the hospital. It is too soon, however, to judge of its effects. The improvement in no one of these cases is rapid, but we trust that it is certain. We look to God alone for the success for which we venture to hope. I can find no statistics which will enable me to give you the number of victims that have fallen under this dread malady of Tracadie. I find, however, a letter from M. Gauvreau, bearing the date of November 30, 1859, that sixty persons perished from its ravages in the previous fifteen years, and that twenty-five of both sexes, and of all ages, were then inmates of the lazaretto, awaiting there the end of their torments.” In 1862 Mr. Gordon said that he saw twenty-three patients at the hospital, and the Sisters of the Hôtel Dieu found twenty there when they reached the lazaretto, and have since admitted three in addition; it does not seem, therefore, as if the “eldest sister of Death” had relaxed her hold on this unhappy village. Yet if the disease can but be confined to this locality, wonders will be achieved. Good care, regular medical attendance, incessant vigilance, with intelligent adherence to hygienic laws, may eventually cause its entire disappearance from our soil. Let us hope that the faithful sisters will succeed in their good work; for we ourselves, every one of us, have a personal interest in it. Unfortunately, this
- 70. good result is far from certain, as the Abbé Gauvreau desires us to understand. “One or more of these unfortunates,” he says, “feeling the insidious approaches of the disease, and shrinking from the idea of the lazaretto, have at times secretly escaped from Tracadie. They leave Miramichi on the steamer, intending to land at Rivière-du-Loup, at Kamouraska, perhaps at Quebec or at Montreal. As yet no ulcers are visible, nor, indeed, any external symptoms which could excite the smallest suspicion. On landing at some one of the places mentioned they procure situations in different houses, and remain in them for a month or two, perhaps, saying nothing all this time of their symptoms to any one, not even to a physician. They eat with their master’s family, and, even if they take the greatest precaution, they convey this poisonous virus to their masters. When they have reason to fear that suspicion is about being aroused, they depart, but it is too late, and they go to scatter the contagion still further. “The following instance came under my own observation: A youth suffering from this disease, and dreading the lazaretto, went to Boston, where he secured a position on a fishing vessel, hoping that the sea air, with the medicines that he would take, would effect his cure. He soon found that these hopes were groundless, and was obliged to enter the hospital in Boston, where, in spite of the care and attention bestowed upon him by the physicians of the medical school at Cambridge, he died, far from friends and home.” One naturally asks, with a thrill of horror, whether, before the admission of this poor creature to the hospital, he did not transmit to his shipmates the poisonous virus that filled his own blood. The total disappearance of this disease—if such disappearance may be hoped for—will be due exclusively to the noble and untiring exertions of the sisters. Tracadie and its afflicted population would not alone owe a debt of eternal gratitude to these Hospital Nuns.
- 71. America itself would share this feeling. With an example like this of charity and self-abnegation before us, we cannot cease to wonder at, and to deplore, the narrow minds of those persons who condemn the monastic institutions of the church. Let us compassionate all such; for to them light is lacking, and they have yet to learn the great truth that the duty most inculcated by the church, after the love of God, is the love of our neighbors.
- 72. TESTIMONY OF THE CATACOMBS TO SOME OF THE SACRAMENTS. In a former article,[31] whilst following Mr. Withrow and other Protestant controversialists through their evasions and misinterpretations of the evidence to be found in the Catacombs on behalf of certain points of Catholic doctrine and practice, we pointed out that prayers either for the dead or to them were the only two articles on which it would be reasonable to look for information from the inscriptions on the gravestones. We said that these prayers were likely to find expression, if anywhere, by the side of the grave. As they took their last look on the loved remains of their deceased friend or relative, the affectionate devotion of the survivors would naturally give utterance either to a hearty prayer for the everlasting happiness of him they had lost, or to a piteous cry for help, an earnest petition that he would continue to exercise, in whatever way might be possible under the conditions of his new mode of existence, that same loving care and protection which had been their joy and support during his life; or sometimes both these prayers might be poured forth together, according as the strictness of God’s justice, or the Christian faith and virtues of the deceased, happened to occupy the foremost place in the petitioner’s thoughts. When, therefore, we proceeded in a second paper to question the same subterranean sanctuaries on another subject of Christian doctrine—the supremacy of St. Peter—we called into court another set of witnesses altogether: to wit, the paintings of their tombs and chapels. Exception has been taken against the competency of these witnesses, on the plea that they are not old enough; they were not contemporary, it is said, with those first ages of the church whose faith is called in question. To this we answer that the objection is
- 73. entirely out of date; it might have been raised twenty or thirty years ago, and it might have been difficult at that time satisfactorily to dispose of it. Those were days in which writers like M. Perrot in France could affect to pronounce dogmatically on the age of this or that painting, solely on the evidence of its style, without having first established any standard by which that style could be securely judged. There are still a few writers of the same school even at the present day, such as Mr. Parker in England, who assigns precise years as the dates of these subterranean monuments with as much confidence as if he had been personally present when they were executed, and (we may add) with as wide a departure from the truth as if he had never seen the pictures at all. Such writers, however, have but few disciples nowadays. Their foolish presumption is only laughed at; and it is not thought worth while seriously to refute their assertions. Men of intelligence and critical habits of thought are slow to accept the ipse dixit of a professor, however eminent, upon any subject; and all who have studied this particular subject—the paintings in the Catacombs—are well aware that the question of their antiquity has now been carried beyond the range of mere conjecture and assumption; it has been placed on a solid basis of fact through the indefatigable labors of De Rossi. Those labors have been directed in a very special way towards establishing the true chronology of the several parts of the Catacombs; and when this had been done, it was manifest to all that the most ancient areæ were also those which were most abundantly decorated with painting, whilst the areæ that had been used more recently—i.e., in the latter half of the fourth or beginning of the fifth century—were hardly decorated at all. This gradual decline of the use of pictorial decoration has been traced with the utmost exactness through the successive areæ of a single Catacomb; six or seven tombs being found thus decorated in the first area, two in the second, one in the third, none at all in the fourth; and the same thing has been seen, with more or less distinctness, throughout the whole range of subterranean Rome. Then, again, every casual visitor to them can see for himself that before the abandonment of burial here—i.e., before the year 410—many of the paintings were already considered
- 74. old enough to be sacrificed without scruple to the wishes of those who would fain excavate new tombs in desirable sites. Men do not usually destroy to-day the paintings which they executed yesterday; certainly they do not allow the ornamentation which they have just lavished on the tombs of their fathers to be soon effaced with impunity. We may be sure, then, that those innumerable paintings which we see broken through in order to make more modern graves must have been of considerable antiquity at the time of their destruction. Then, again, it must not be forgotten that some of these paintings were actually appealed to as ancient testimony in the days of St. Jerome, on occasion of a dispute between that doctor and St. Augustine as to the correct rendering of a particular word in his Latin translation of the Scriptures. Finally, it is notorious that the fine arts had rapidly decayed and the number of their professors diminished before the days of Constantine—in fact, before the end of the third century. We cannot, however, pretend to give in these pages even a brief summary of De Rossi’s arguments and observations whereby he establishes the primitive antiquity of Christian art in the Catacombs. We can only mention a few of the more popular and palpable proofs which can be appreciated by all without difficulty; and we will only add that it is now possible, under the sure chronological guidance of De Rossi, to distinguish three successive stages in the development of painting in the Christian cemeteries, the latest of which was complete when the Constantinian era began, and the first falls hardly, if at all, short of even apostolic times. This is no longer denied by the best instructed even among Protestant controversialists; they acknowledge that painting was used by the earliest Christians for the ornamenting of their places of burial; only they contend that it was done “not because it was congenial to the mind of Christianity so to illustrate the faith, but because it was the heathen custom so to honor the dead.” The author of this remark, however, has omitted to explain whence it comes to pass that the great majority of the paintings which survive in the cemeteries are
- 75. more engaged in illustrating the mysteries of the faith than in doing honor to the dead. But we must not pursue this subject any further. We have said enough, we think, to establish the competency of these paintings as witnesses to the ancient faith, and we will now proceed to question them concerning one or two principal mysteries of the faith—those that are called its mysteries par excellence: its sacraments. We do not doubt that, if duly interrogated, they will have some evidence to give. We say, if duly interrogated, because it is the characteristic of ancient Christian art to be eminently symbolical; it suggested rather than declared religious doctrines and ideas, and it suggested them by means of artistic symbols or historical types, which must be inquired into and meditated upon before they can be made fully to express their meaning. This is of the very essence of a symbol: that it should partly veil and partly manifest the truth. It does not manifest the truth with the fulness and accuracy of a written historical description, or it would cease to be a symbol; on the other hand, it must not be so obscure as to demand a sibyl for its interpretation; it must have a tendency to produce in the mind of the beholder some leading feature of the object it is intended to represent. And where should symbols of this kind be more abundantly found for the Christian preacher or artist than in the histories of the Old Testament? Ancient Christian art, says Lord Lindsay, “veiled the faith and hope of the church under the parallel and typical events of the patriarchal and the Jewish dispensations.” We need not remind our readers that the principle of this method of interpreting Holy Scripture has express apostolic sanction; but few who have not studied the subject closely will have any adequate idea of the extent to which it was followed in the ancient church. We will give a single example, selected because it closely concerns the first mystery of which we propose to speak—the Sacrament of Baptism. Tertullian, who lived at the end of the second and beginning of the third century, wrote a short treatise on this sacrament. This treatise
- 76. he begins by bringing together all that Holy Scripture contains about water, with such minuteness of detail that he is presently obliged to check himself, saying that, if he were to pursue the subject through all Holy Scripture with the same fulness with which he had begun, men would say he was writing a treatise in praise of water rather than of baptism. From the first chapter of the Book of Genesis to the last of the Evangelists, and even of the Apocalypse, he finds continual testimony to the high dignity and sacramental life-giving power of this element. The Spirit of God, he says, moved over it at the first; whilst as yet the earth was void and empty, and darkness was upon the face of the deep, and the heaven was as yet unformed, water alone, already pure, simple, and perfect, supplied a worthy resting-place on which God could be borne. The division of the waters was the regulating power by which the world was constituted; and when at length the world was set in order, ready to receive inhabitants, the waters were the first to hear and obey the command and to bring forth creatures having life. Then, again, man was not made out of the dry earth, but out of slime, after a spring had risen out of the earth, watering all its surface. All this is out of the first two chapters of Genesis; and here he makes a pause, breaking into that apology which has been already mentioned. Then he resumes the thread of his discourse, but passing much more briefly over the remainder of the Old Testament. He notes how the wickedness of the old world was purged by the waters of the Deluge, which was the world’s baptism; how the waters of the Red Sea drowned the enemies of God’s people and delivered them from a cruel bondage; and how the children of Israel were refreshed during their wanderings through the wilderness by the water which flowed continuously from the rock which followed them, “which rock was Christ.” Then he comes to the New Testament, and briefly but eloquently exclaims: Nowhere is Christ found without water. He is himself baptized with it; he inaugurates in it the first manifestation of his divine power at the wedding-feast in Cana; when he preaches the Gospel, on the last and great day of the feast, he stands and cries, saying, “If any man thirst, let him come to me and drink.” He sums up his whole gift to man under the image of a fountain of
- 77. water, telling the Samaritan woman that he has living water to give, which shall become in him that receives it a fountain of water springing up unto life everlasting. When he gives instruction upon charity, he instances a cup of cold water given to a disciple; he sits down weary at a well and asks for water to refresh himself; he walks on the waves of the sea, and washes his disciples’ feet; finally (Tertullian concludes), “this testimony of Jesus to the Sacrament of Baptism continues even to the end, to his very Passion; for, when he is condemned to the cross, water is not absent—witness the hands of Pilate; nay, when wounded after death upon the cross, water bursts forth from his side—witness the soldier’s spear.” There may be something in this symbolism that sounds strange to modern ears; but we are not here criticising it; we have nothing to do with its merits or demerits, but only with the fact of its general use—so general that it was the one principle of exegesis which every commentator on Holy Scripture in those days followed, and we have every right to suppose that Christian artists would have followed it also. When, therefore, we find in the Roman Catacombs (as, for example, the other day in the cemetery of San Callisto) a glass vessel, very artistically wrought, with fishes in alto rilievo swimming round it in such a way that, when full of water, it would have represented a miniature image, as it were, of the sea, is it a mere fanciful imagination which bids us recognize in such ornamentation a reference to holy baptism, and conjectures that the vessel was perhaps even made for the administration of that sacrament? It may be so; but we cannot ourselves think so; we cannot at once reject the explanation as fanciful; the work of the artist corresponds too exactly with the words of the theologian to allow us to treat the coincidence as altogether undesigned. “We little fish are born,” says Tertullian, “after the likeness of our great Fish in water, and we cannot otherwise be safe than by remaining in the water.” And we seem to ourselves to read these same words, written in another language, in the beautiful vessel before us. We read it also in another similar vessel, which looks as though it had come out of the same workshop, yet was found in an ancient cemetery at Cologne;
- 78. and in another of bronze, dug up in the vineyard over the cemetery of Pretextatus, that used to be shown by Father Marchi in the Kircherian Museum at the Roman College. In all these instances we believe that this is the best account that can be given, both of the original design of the vessel and also of its preservation in Christian subterranean cemeteries. However, if any one thinks otherwise, we do not care to insist upon our explanation as infallibly certain. We will descend into the Catacombs themselves, and look about upon the paintings on their walls or the carving on their gravestones, and see whether baptism finds any place there also. And, first, we come across the baptism of our Lord himself. We are not now thinking of the subterranean baptistery in the cemetery of Ponziano, with the highly-decorated cross standing up out of the middle of it, and Christ’s baptism painted at the side. For this is one of the latest artistic productions in the Catacombs—a work of the eighth or ninth century possibly. We are thinking, on the contrary, of one of the earliest paintings in a most ancient part of the excavations, in the crypt of Lucina, near the cemetery of Callixtus, with which, in fact, it is now united. We shall have occasion to return to this same chamber presently for the sake of other paintings on its walls having reference to the Holy Eucharist; just here we only call attention to the baptism of our Lord, which is represented in the space over the doorway. We do not know of any other instance of this subject having been painted in the Catacombs besides the two that we have mentioned, but it is quite possible that others may be hereafter discovered; but of baptism as a Christian rite, veiled, however, under its types and symbols, we have innumerable examples. Few figures recur more frequently among the paintings in the Catacombs, and none are more ancient, than that of a man standing in an open box or chest, often with a dove, bearing an olive-branch in its mouth, flying towards him. When this was first seen after the rediscovery of the Catacombs in the sixteenth century, men set it down to be the picture of some ancient bishop preaching in a pulpit, and the Holy Ghost, under the form of a dove, inspiring him as to
- 79. what he should say, according to the legend told of St. Gregory the Great and some others. Nobody now doubts that it was intended for Noe in the ark; not, however, the historical Noe and the historical ark —for nothing could be more ludicrously false to the original—but those whom that history foreshadowed: Christians saved by the waters of baptism and securely housed in the ark of the church. Some persons, who seem to take a perverse delight in assigning a pagan rather than a Christian origin to everything in the early church, account for the difference between the Biblical and the artistic representation of the ark by saying that the Christian artist did but copy a pagan coin or medal which he found ready to his hands. It is quite true that certain coins which were struck at Apamea in Phrygia during the reigns of Septimius Severus, Macrinus, and Philip the elder—i.e., at different periods in the first half of the third century—exhibit on one side of them a chest, with a man and a woman standing within it, and the letters ΝΩ, or ΝΩΕ, written on the outside; and that these figures were intended to be a souvenir of the Deluge, which held a prominent place in the legends of Phrygia. It is said that the town of Apamea claimed to derive its secondary name of κιβωτός, or ark, from the fact that it was here that the ark rested; and it is quite possible that the spread of Christian ideas, gradually penetrating the Roman world, and filtering into the spirit even of those who remained attached to paganism, may have suggested the making of the coins we have described; but it is certain, on the other hand, that we can claim priority in point of time for the work of the Christian artists in the Catacombs. The coins were struck, as we have said, in the beginning of the third century; the earliest Christian painting of the same subject is assigned to the beginning of the second. But whatever may be the history of the forms under which Noe and the ark are represented, there can be no question as to their meaning. We have the authority of St. Peter himself (1 iii. 20, 21) to instruct us upon this point; and Tertullian does but unfold what is virtually contained in the apostle’s words when he says that the ark prefigures the church, and that the dove sent out of the ark and
- 80. returning with an olive-branch was a figure of the dove of the Holy Spirit, sent forth from heaven to our flesh, as it emerges from the bath of regeneration. And if we quote Tertullian again as our authority, this is not because he differs in these matters from other Christian writers who preceded or followed him, but because he has written at greater length and specially on that particular subject with which we are now engaged. St. Augustine, writing two hundred years later, gives the same explanation, and says that “no Catholic doubts it; but that it might perhaps have seemed to be a merely human imagination, had not the Apostle Peter expressly declared it.” It is, then, from no private fancy of our own, but simply in conformity with the teaching of all the ancient doctors of the church, that we interpret this scene of a man standing in an ark, and receiving an olive-branch from the mouth of a dove, as expressing this Christian doctrine: that the faithful obtain remission of their sins through baptism, receive from the Holy Spirit the gift of divine peace —that peace which, being given by faith in this world, is the gage of everlasting peace and happiness in the next—and are saved in the mystical ark of the church from the destruction which awaits the world. And if the same scene be rudely scratched on a single tomb, as it often was, and sometimes with the name of the deceased inscribed upon the chest, we can only understand it as denoting a sure and certain hope on the part of the survivors that their departed friend, having been a faithful member of the church, had died in the peace of God and had now entered into his rest. We pass on to another of the Biblical stories mentioned by several of the Fathers as typical of baptism; and we will select as our specimen of it a painting that was executed about the very time that Tertullian was writing his treatise on that sacrament. It is to be seen more than once on the walls of a series of chambers which open out of a gallery in the Catacomb of San Callisto, not far from the papal crypt. The first figure that greets us from the wall on the left-hand side as we enter these chambers is Moses striking the rock and the water gushing forth. Are we to look upon this as a mere historic souvenir of the Jewish legislator, or are we to see in it a reference to Christian
- 81. baptism? The artist in the present instance does not allow us to doubt. Side by side with it he has painted a fisherman, and we need not be reminded who it was that compared the work of the Christian apostle to that of fishermen; and immediately he adds, with still greater plainness of speech, a youth standing in the water, whilst a man pours water over his head. Finally, he fills the very little space that remains on the wall with the picture of a paralytic carrying his bed, and it would be easy to show that the Fathers recognized in the pool of Bethsaida, to which place this history belongs, a type of the healing waters of baptism. Was it possible for the Christian artist to set forth the sacrament more unequivocally? There is no legend to interpret the painting, but surely this is not needed. The mystery is veiled, indeed, from all who were uninstructed; but it was perfectly intelligible to all the baptized; it was veiled under types and symbols taken partly from the Old Law and partly from common life. We need hardly say that this same figure of Moses striking the rock occurs in scores of other places throughout the Catacombs; but we have selected this particular specimen, both because it appears with a more copious entourage of other symbols determining its sense beyond all dispute, and also because it is here brought, as we shall presently see, into immediate proximity with the other sacrament, to which it is a necessary gate of introduction—the Sacrament of the Holy Eucharist. But before we pass on to examine the symbols of the Holy Eucharist, let us first inquire whether there is anything further about baptism to be gleaned from the Catacombs—not now from their paintings, but from their inscriptions. We must remember that the most ancient inscriptions were very brief—very often the mere name of the deceased and nothing more, or a short ejaculatory prayer was added for his everlasting happiness. It is clear that we should search here in vain for any mention of the sacraments. By and by, when it became usual to say something more about the deceased, to mention his age and the date of his death or burial, or other similar particulars, perhaps room might be found also for saying something about his baptism. Accordingly, there are not wanting monuments of the fourth or fifth
- 82. centuries which tell us that the deceased was a neophyte, or newly illuminated—which means the same thing: viz., that he had been lately baptized—or that he had lived so many months or years after he had received the initiatory sacrament of the Christian covenant. Occasionally, also, a faint reference may be found to another sacrament—the Sacrament of Confirmation. This was often, or even generally, administered in olden times immediately after baptism, of which it was considered the complement and perfection. “From time immemorial,” says Tertullian (ab immemorabili), “as soon as we have emerged from the bath [of regeneration] we are anointed with the holy unction.” Hence it is sometimes doubtful which sacrament is intended, or rather it is probable that it was intended to include both under the words inscribed on the epitaphs—the verbs accepit, percepit, consecutus est (the same as we find in the fathers of the same or an earlier age), used for the most part absolutely, without any object whatever following them; but in one or two cases fidem or gratiam sanctum are used. An epitaph of a child three years old adds: Consecuta est D. vi. Deposita viii. Kal. Aug. Another says simply: Pascasius percepit xi. Kal. Maias; and a third: Crescentia q. v. a. xxxiii. Accepit iii. Kal. Jul. A fourth records of a lady that she died at the age of thirty-five: Ex die acceptionis suæ vixit dies lvii.; to which we append another: Consecutus est ii. Non. Decemb. ex die consecutionis in sæculo fuit ad usque vii. Idas Decemb. This last inscription is taken from a Christian cemetery in Africa, not in Rome; but it was worth quoting for its exact conformity with the one which precedes it. In both alike there is the same distinction between the natural and the spiritual age of the deceased—i.e., between his first and his second birth. After stating the number of years he had lived in the world, his age is computed afresh from the day of his regeneration, thus marking off the length of his spiritual from that of his merely animal life. A Greek inscription was found a few years since on the Via Latina, recording of a lady who had belonged to one of the Gnostic sects in the third century, that she had been “anointed in the baths of Christ with his pure and incorruptible ointment”—an inscription which
- 83. probably refers to two separate rites in use among the Gnostics, in imitation of the two Christian sacraments. Of a Christian lady buried in Spoleto, her epitaph records that she had been confirmed (consignata) by Pope Liberius; this, of course, belongs to the middle of the fourth century. And we read of a boy who died when he was a little more than five years old: Bimus trimus consecutus est—words which were a veritable enigma to all antiquarians, until the learned Marini compared with them the phrases of Roman law, bima trima die dos reddita, bima trima die legatum solutum, and pointed out that as these phrases undoubtedly signified that such a portion of the dowry or legacy was paid in the second year, and such another portion in the third, so the corresponding words in the Christian epitaph could only mean that the deceased had received something when he was two years old, and something else when he was three; and although the particular gifts received are not mentioned because of the disciplina arcani, we can have no difficulty in supplying baptism and confirmation. De Rossi adopts this interpretation; indeed, it does not seem possible to suggest any other. It seems, then, that there is not much evidence to be derived from the Catacombs as to the Sacrament of Confirmation; that, on the contrary, which has reference to the Holy Eucharist is most precious and abundant, and it is generally to be found in juxtaposition with monuments which bear testimony to the Sacrament of Baptism. The chamber in the crypt of Lucina which gives us the oldest painting of the baptism of our Lord gives us also what are probably the oldest symbolical representations of the Holy Eucharist; and certainly the chambers in the cemetery of San Callisto, in which we have just seen so many and such clear manifestations of the Sacrament of Baptism, contain also the most numerous and the most perfect specimens of the symbolic representations of the Holy Eucharist carried to their highest degree of development, yet still combined with mysterious secrecy. Before enumerating these in detail it will be best to make two or three preliminary remarks helping to clear the way before us. First, then, we may assume as known to all our readers, both that the doctrine about the Blessed Sacrament
- 84. belonged in a very special way to the discipline of the secret, and also that from the very earliest times one of the most common names under which our Blessed Lord was spoken of was the fish, because the letters which go to make up that word in Greek were also the initials of the words Jesus Christ, Son of God, Saviour. And, secondly, we must say a few words about the different circumstances under which a fish appears in the artistic decorations of the Catacombs; at least, of the different kinds of feasts or entertainments in which it seems to be presented as an article of food. These feasts may be divided into three classes: First, the fish merely lies upon a table—a sacred table or tripod—with one or more loaves of bread by its side, and not unfrequently with several baskets full of bread on the ground around it; secondly, bread and fish are seen on a table, at which seven men are seated partaking of a meal; and, thirdly, they are seen, perhaps with other viands also, at a feast of which men and women are partaking indiscriminately, and perhaps attendants also are there, waiting on the guests, pouring out wine and water, hot or cold. Paintings of this latter class have not uncommonly been taken as representing the agapæ, or love-feasts, of the early church. But this seems to be too literal an interpretation, too much out of harmony with the symbolical character of early Christian art. More probably it was meant as a representation of that wedding-feast under which image the joys of heaven are so often set forth in Holy Scripture; and in this case it is not necessary to suppose that there was any special meaning in the choice of fish as part of the food provided, unless, indeed (which is not at all improbable), it was desired to direct attention to that mystical food a participation in which was the surest pledge of admission to that heavenly banquet, according to our Lord’s own words: “He that eateth this bread shall live for ever.” However, it is not necessary, as we have said, to suppose this; it is quite possible that in these instances the fish may have been used accidentally, as it were, and indifferently, or for the same reason as it sometimes appears on pagan monuments—viz., to denote the abundance and excellence of the entertainment.
- 85. Paintings of the first class, however, are much too peculiar to be thus explained, neither is there anything resembling them in the works of pagan artists which could have suggested them; and those of the second class, we hope presently to show, can only have been intended to represent a particular scene in the Gospel history. It is only with paintings belonging to one or other of these two classes that we need concern ourselves to-day. And, first, of the bread and fish when placed alone, without any guests at all. In the crypt of Lucina it appears twice on the wall opposite our Lord’s baptism, and in a very remarkable form indeed. The fish is alive and apparently swimming, and he carries on his back a basket full of loaves, in the middle of which is a vessel of glass containing some red liquid. What can this mean? Nobody ever saw anything like it in nature. We know of nothing in pagan art or mythology which could have suggested it. Yet here it finds a place in the chamber of a Christian cemetery, and as part of a system of decoration, other parts of which were undoubtedly of a sacred character. Is this alone profane or meaningless, or does not rather its hidden sense shine forth distinctly as soon as we call to mind the use of the fish as a Christian symbol on the one hand, and the Christian doctrine about the Holy Eucharist on the other? The fish was Christ. And he once took bread and broke it, and said, This is my body; and he took wine and blessed it, saying, This is my blood; and he appointed this to be an everlasting ordinance in his church, and promised that whosoever should eat of that bread and drink of that chalice should inherit everlasting life. Here are the bread and the wine and the mystical fish. And was it possible for Christian eyes to attach any other meaning to the combination than that it was intended to bring before them the remembrance of the Christian mysteries, whereby death and the grave were robbed of all their gloom, being only the appointed means of entrance to a never-ending life? If anybody is tempted to object that the vessels here represented as containing the bread and wine are too mean ever to have been used for such a purpose, we must remind him that it had already been put on record by archæologists, before the discovery of this monument, that the early Christians in the days of poverty and persecution continued to
- 86. use vessels of the same humble materials as had been used in the sacrificial rites of Jews and Gentiles before them, and that these were precisely such as are here represented. Nay, further still, that even when vessels of gold and silver had come into use in the church, still there were exceptional times and circumstances when it was lawful, and even praiseworthy, to return to the more simple and ancient practice. St. Jerome praises St. Exuperius, Bishop of Toulouse in his day, because, having sold the church-plate to relieve the pressing necessities of the poor, he was content to carry the body of Christ in a basket made of wicker-work, and the blood of Christ in a chalice of glass. Most assuredly St. Jerome would have been at no loss to interpret the painting before us. But let us now pass on into the cemetery of San Callisto, and enter again the chamber in which we saw Moses, and the fishermen, and the ministration of baptism, and the paralytic. Let us pursue our walk round the chamber, and immediately after the paralytic, on the wall facing the doorway, we come to the painting of a three-legged table with bread and fish upon it, a woman standing on one side in the ancient attitude of Christian prayer, and a man on the other stretching out his hands over the fish and the bread, as though he were blessing them. Can it be that we have here the act of consecration of the Holy Eucharist, as in the adjacent wall we had the act of baptizing, only in a somewhat more hidden manner, as became the surpassing dignity of the greater mystery? Nobody, we think, would ever have disputed it, had the dress of the consecrator been somewhat more suited to such an action. But his breast and arm and one side of his body are considerably exposed, as he stretches out his arm from underneath his cloak; and modern taste takes exception to the exposure as unseemly in such a time and place. We have no wish to put a weapon into the hands of the anti- ritualistic party. Nevertheless, we believe that it is pretty well ascertained that at first no vestment was exclusively appropriated to the celebration of Mass. We are not sure that Dean Stanley was in error when he wrote the other day that St. Martin, the Apostle of Gaul and first Bishop of Tours, wore a sheepskin when he officiated,
- 87. Welcome to our website – the perfect destination for book lovers and knowledge seekers. We believe that every book holds a new world, offering opportunities for learning, discovery, and personal growth. That’s why we are dedicated to bringing you a diverse collection of books, ranging from classic literature and specialized publications to self-development guides and children's books. More than just a book-buying platform, we strive to be a bridge connecting you with timeless cultural and intellectual values. With an elegant, user-friendly interface and a smart search system, you can quickly find the books that best suit your interests. Additionally, our special promotions and home delivery services help you save time and fully enjoy the joy of reading. Join us on a journey of knowledge exploration, passion nurturing, and personal growth every day! ebookbell.com