Different technique for investigation of fiber structure..

Md. Ferdus Alam ID: 2011000400018 Page 1
Different technique for investigation of fiber structure
Introduction:
Cotton, silk and wool which are the fibers commonly used in the textile industry have recently
found competitors in various synthetic products, viz., rayon, nylon and the rest. The
technological importance of knowledge of the properties of all such fibers has naturally resulted
in a great deal of attention being devoted to the investigation of their molecular structure. Fiber
molecular structure is investigated by different method. Using different method to determine the
chemical groups, molecular spacing, chemical bonding, crystallinity, orientation, spiral turns,
molecular packing, cross-sectional shape of fiber.
Fig: Fiber structure.
Methods of fiber structure investigation:
The elucidation of fiber structure has been based on many sources of information, which include:
1) X-ray diffraction method
2) Infra-red radiation method
3) Electron microscopic method
4) Optical microscopic method
5) Thermal analysis
6) Nuclear magnetic resonance (NMR) method
7) Density
8) General physical properties
9) The chemistry of fiber material
10) Raman scattering of light
Absorption of infrared radiation:
The chemical structure of the fiber volume is investigated by infrared absorption spectroscopy.
Infrared absorption spectroscopy, broadly applied to analyze polymer structures, is also
employed as a method of studying fiber structures and their changes. This is one of the
instrumental methods commonly applied in Fiber Physics for the purpose of qualitative and

quantitative analyses of fiber orientation, studies of fiber crystalline structure, and selective
evaluation of the structure of fiber surface layers, as well as the effects of superficial and
volumetric modification of fiber structures.
Fig: Infrared absorption spectroscopy.
Properties of Infra- red radiation absorption method:
1) Determination of spiral turns or convolution of cotton fiber
2) Determination of molecular spacing
3) Determination of chemical bonding
4) Determination of degree of crystallinity & orientation
5) Determination of molecular packing
6) Determination of cross-sectional shape of fiber
7) Identifications of fiber
By using an infrared spectrometer, the variation in absorption can be found and plotted against
wave length or, more commonly, its reciprocal, the wave number. This is illustrated in the figure,
which is the absorption spectrum of nylon. The peaks occur where the frequency of the
electromagnetic waves corresponds with the natural frequency of vibration between two atoms in
the material. If these are associated with an electric dipole, then the variations in the electric field
set up the vibration, and energy is absorbed from the radiation. The fundamental oscillations
occur at wave numbers less than 4000 cm–1. These give strong absorptions and so can be studied
only in very thin films or fibers. At higher wave numbers, nearer optical frequencies, absorptions
will occur that are due to harmonics of the fundamental frequencies. The absorption spectrum in
this range is more complex and less used, but, since the absorptions are weaker, thicker
specimens, such as fiber bundles, can be studied.
Fig: Crystal structure of poly amide fiber.

The wave number at which absorption takes place depends primarily on the nature of the two
atoms and of the bond between them. Thus there will be absorption frequencies characteristic of
such groupings as C- H, C= O, C-O- , -O- H, N -H, C-C, C=C and so on. To a smaller extent, the
absorption frequency is influenced by the other groups in the neighborhood: for example, the
absorption frequency for a carbon–hydrogen bond in a terminal group,
—CH3, is different from that for the same bond in a chain, —CH2—.
The first use of infrared absorption is therefore as an aid to the identification of the presence of
certain groups in the molecule, leading to the determination of its chemical formula. The method
can also be used in routine analysis to identify and estimate quantitatively the presence of given
substances, even in small quantities in a mixture, by observation of their characteristic spectrum.
For instance, it can be used to determine the amount of water in fibers.
Other structural information can also be obtained. In fiber orientation studies the experimental
basis are the absorption spectra of linearly polarized IR radiation applied parallel and
perpendicular to the axis of the irradiated fiber.
This takes to develop an adequate so-called web preparation being a mono fibrous layer of
compact and parallel fibers. The study produces two IR absorption spectra with discernible
absorption bands correlated with the relevant relative ordered states of macromolecules, so-
called ―crystalline‖, ―amorphous‖, and ―independent‖ bands
Fig: Polarized IR radiation of Poly Amide fiber.
This provides the basis for fiber orientation analysis in terms of the ordered state separately for:
crystallites, macromolecules in non-crystalline material, and the resultant – as total. The
indicator in the quantitative evaluation of fiber orientation is the value of the dichroism quotient
R which expresses the intensity ratio of the diachronic absorption band appropriate for the
parallel irradiation of the fiber to the intensity of that absorption band found in the spectrogram
for the perpendicular irradiation of the sample.
The more the R value diverges from 1, the higher is the fiber orientation level. The quantitative
fiber orientation indicators are determined based on certain experimental relationships

An advantage of the infrared absorption method is that it is influenced by all the molecules in the
fiber, in both the crystalline and non-crystalline regions, whereas the X-ray diffraction method
gives detailed information only about the crystalline regions of the fiber. For example, the
infrared spectrum gives evidence of the presence of α- and β-forms of protein molecules in the
non-crystalline regions of protein fibers.
X-ray diffraction method:
Diffraction is the study of the particular patterns that may be found when waves pass through or
round objects of particular shape. X-ray diffraction is a most important tool for the study of fiber
structure, firstly because it gives information at the most important level of fine structure, and
secondly because focusing of X-rays is not possible, so that diffraction methods have to be used.
X- Ray diffraction is used to measure the nature of polymer and extent of crystallite present in
the polymer sample.
Properties of x-ray diffraction method:
1) Determination of chemical groups
2) Determination of molecular spacing
3) Determination of chemical bonding
4) Determination of degree of crystallinity & orientation
5) Determination of water absorption
Crystalline regains in the polymer scatted in well defined manner acts as diffraction grating.
Polymer contain both crystalline and amorphous phase within arranged randomly. When beam
of X- ray passed through the polymer sample, some of the regularly arranged atoms reflect the
X- ray beam constructively. Amorphous sample gives sharp arcs since the intensity of emerging
rays are more where as crystalline sample incident rays get scattered. Arc length of diffraction
pattern depends on orientation. If the sample is highly crystalline, smaller will be the arc length.
Fig: X-ray-diffraction photographs of fibers.

From the above figure, the symmetrical pattern of sharp spots is clearly apparent. The patterns in
the figures are much less sharp, but the way in which they deviate from the idealized pattern
yields extremely valuable information about fiber structure. For example, if the orientation is not
completely perfect, one can get reflections over a range of angles, and the spots broaden out into
arcs. The transition from a fiber with no preferred orientation of the crystals, through a
moderately oriented fiber, to a highly oriented one is shown in Figs: (a), (b) and (c) for a
regenerated-protein fiber, wool and silk, respectively. The X-ray diffraction photographs of
fibers may be used for various purposes.
Since the patterns for each type of fiber are different, as illustrated in the figure, they may be
used for identification, but their main use is to give information about fiber structure. If the
position of a large enough number of spots is known with sufficient accuracy, then the exact
crystal structure in which the molecules are packed can be worked out, and this has been done
for several fibers. Even when there is not sufficient information to do this, one can deduce much
that is useful. If the patterns are different, then the crystal structure must be different.
Fig: X-ray-diffraction photographs of fibers.
For example, there is a slight difference in the spacing of the spots in Figs (d) and (e) for hemp
and Fortisan, respectively.
This shows up the difference in the crystal structures of native and regenerated celluloses.
The broadening of the spots into arcs shows a decrease in the degree of orientation. This is
illustrated in Figs (e), (f), and (g) for Fortisan, high-tenacity viscose rayon and ordinary viscose
rayon. The arcs in these photographs gradually diminish in intensity as the distance from the
middle of the arc increases. But, in the photograph for cotton Fig.(h), the arcs end sharply: this is
due to the fact that the crystals are arranged on spirals round the fiber axis, so the range of
orientations relative to the fiber axis is sharply defined. From the angles subtended by the arcs,
one can calculate the spiral angle in the fiber. In a few special materials, such as porcupine quills,
sharp reflections have been obtained, indicating the presence of some repeat in the structure at a
large spacing, but usually a diffuse halo is found. This is due to the scattering of X-rays by small
crystallites in the fiber.

Optical diffraction method:
Optical diffraction is a useful source of information about fiber structure. In particular, the
orientation of the polymer molecules can be estimated from optical diffraction method. When a
beam of light is passed through a photographic slide, the light is scattered in many directions. By
using a lens in the right place, we can recombine this scattered information about the picture into
an image on a screen. But the information is there before it is recombined, and diffraction is the
science of understanding and using this information in all sorts of ways. Image formation is thus
merely one branch of diffraction in its most general sense, and there are many circumstances in
which images cannot be formed or are not the most useful means of obtaining the required
information about the object. An example of the use of optical diffraction in fiber physics is
shown in the figure.
Fig: Diffraction pattern of poly amide fiber.
A single fiber will diffract a parallel beam of light into a pattern of fringes that gives a means of
measuring its diameter accurately or of showing up changes in diameter. If the fiber is gold
coated, as in the figure, the pattern is relatively simple, since all the scattering is from the edge of
the fiber; but if light also passes through the fiber and is scattered internally, a much more
complicated pattern is found. In this pattern, there must be a great deal of useful information on
internal fiber structure .The problem is how to understand the phenomenon in sufficient detail to
extract this information.
The scattering of a fine beam of light is another diffraction phenomenon that can be used to
obtain information about the internal structure of polymer films, which may be related to fiber
structure. This is analogous to the formation of a halo round the moon when it is seen through a
cloud. The radius and breadth of the halo give some information about the distribution of
spacing’s between the particles that scatter the light, for example, the crystallites within a fiber.
More complicated patterns can also be made to yield information about the shape of the
scattering particles and differences in spacing in different directions.
Optical-diffraction effects, including optical microscopy, even by using ultraviolet radiation, will
therefore give information only on relatively coarse features of fiber structure with spicing
greater than about 0.1 μm. Indeed, optical microscopy becomes very difficult as soon as one
approaches 1 μm, which is not much less than typical fiber diameters. Atomic and molecular
spacing are more than a thousand times smaller than this: typical values lie between 0.1 and 0.5
nm.

Consequently, in order to obtain information about the fine structure of fibers, we need to use
much shorter electromagnetic waves.
Fig: Optical Microscope.
Nuclear magnetic resonance (NMR) method:
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a
research technique that exploits the magnetic properties of certain atomic nuclei to determine
physical and chemical properties of atoms or the molecules in which they are contained. It relies
on the phenomenon of nuclear magnetic resonance and can provide detailed information about
the structure, dynamics, reaction state, and chemical environment of molecules. As usual in
resonance phenomena, the energy absorbed can be caused to vary in two ways: in this system,
either by scanning through a range of frequencies, with a maximum at the resonant frequency, or
by running through a change of magnetic field at constant frequency. The latter procedure is
usually adopted, and a typical response for a solid polymer is shown in the figure. Differentiation
of the curve aids interpretation. The ratio of the intensity of the broad band to the intensity of the
narrow band gives a measure of the crystalline/non-crystalline ratio in the material.
Fig: Nuclear magnetic resonance curve for a solid polymer & digital NMR spectroscopy.

What is even more interesting is the fact that the width of the broad band gives a measure of the
rigidity of the more highly ordered material. Statton has shown that this decreases with
temperature owing to the increasing thermal oscillation in the crystal lattice, but it is also
interesting that it increases on drawing nylon and increases still more on hot stretching.
Statton, as indicated in the figure terms the parameter derived from the broadband width the
matrix rigidity, since the width depends on how firmly the resonating atom is held within the
surrounding matrix of highly ordered material. In a perfect crystal, the width would be great; in a
small or defective crystal, it would be less. In a similar way, the width of the narrow band could
indicate how firmly individual atoms are held within their matrix of less ordered regions.
Raman scattering of light method:
Raman scattering is the inelastic scattering of photons. By measuring the peak positions relative
to the incident light is possible to measure the energy of the normal modes of vibration, and
through symmetry and selection rule considerations it is possible to identify the symmetry and
chemical structure of the examined molecules. A general overview of the Raman Effect, along
with the origin of the selection rules and a comparison with infrared absorption is given. Modern
uses of Raman spectroscopy are listed, and two particular practices are summarized, including
the measurement of stresses inside a crystal, and the measurement of superconducting gaps.
Fig: Raman Spectroscopy
Light scattering from particles much smaller than the wavelength can be divided into two
categories: Rayleigh scattering, in which the incident photon is scattered elastically and its
frequency remains unchanged, and Raman scattering, in which the incident photon inelasticity
scatters and is noted by a shift in frequency. The second effect, named after C.V. Raman who
was the first along with K.S. Krishnan to observe the phenomenon in 1928, was first
theoretically predicted by A. Smekal in 1923. It is observed experimentally, as pairs of peaks
shifted from the incident frequency by amounts ±! If as the scattering molecules can both absorb
energy from the photon decreasing its frequency, or donate energy to the photon increasing its
frequency.

It is important to note that Raman scattering is not the absorption of the photon, followed by the
emission of a photon of less energy that instead describes fluorescence. The key difference
between Raman scattering and fluorescence is that in Raman scattering the incident photon is not
fully absorbed and instead perturbs the molecule exciting or de-exciting vibration or rotational
energy states. Contrastingly, in fluorescence the photon is completely absorbed causing the
molecule to jump to a higher electronic state, and then the emitted photon is due to the
molecule’s decay back to a lower energy state. To better understand the difference, consider that
a quencher may be added to allow non-photonic de-excitation of a molecule, by providing an
alternative means of energy decay and therefore reducing the fluorescence intensity. However,
no such quencher can be added for Raman scattering because the photon serves simply as a
perturbation to the molecule.
At first glance, the fact that Raman scattering allows for the measurement of vibration and
rotational states would seem to make it irrelevant when compared to infrared absorption which
also has the capabilities to probe the energies of those states. However, a more in-depth analysis
reveals that Raman and infrared absorption are more complimentary than competing techniques,
and that the most information about a molecule can be attained by comparing the two spectra as
energy transitions allowed by one process, may be forbidden by the other, and vice versa.
Indeed, taken together, the techniques can reveal not only the energies of the vibration states, but
also the shape of the molecule by considering the necessary symmetries. A more detailed
explanation of how this is done will be discussed later.
One advantage that Raman scattering has over infrared absorption however, is that since it is
represented as a shift in frequency from the incident light, it can be done with visible light, for
Nielsen 2 which it is possible to create detectors with much higher efficiencies than infrared
radiation. Furthermore, information about the molecule can be gleaned from the polarization of
the Raman scattered light, information which is not easily accessible via infrared absorption. The
disadvantage of Raman is that many of the peaks have extremely small intensities, so much so
that the absence of an expected peak does not necessarily mean that the theoretical prediction is
flawed, but may simply be due to the fact that the expected peak has an intensity that lies below
the noise level of the system. Since Raman is due the light interacting with the vibration and
rotation states of the molecules, it is primarily used to investigate the normal modes of particular
molecules. However, other than allowing a means of measuring the frequency of the normal
modes, the selection rules which govern Raman scattering make it possible to determine the
symmetry group that the molecule belongs to, and thus the physical structure of a molecule. For
example, it can be used to determine if a three atom molecule is linear like CO2 or bent like
H2O. It is primarily used as a fingerprint to identify chemical species as each species has unique
Raman spectra; however it has been found to have a multitude of other uses. In condensed matter
studies Raman scattering is used to investigate the structure of both amorphous and crystalline
solids, measure the internal stresses of a system, identify the nature of contaminants, and probe
the superconducting gap. In bimolecular studies it is useful for examining the structure of
proteins.
Raman spectroscopy has become a powerful tool for investigating fiber structure as a result of
the development of Raman microscopes. With a spot size less than a fiber diameter, spectra can
be obtained from single fibers. If the fiber is mounted on an extension stage in the microscope, it
is possible to observe the shift in the spectral lines with fiber extension. In this way it is possible
to show which parts of the structure are changing. An account of the use of Raman spectroscopy
in various ways in the study of aramid, polyester and carbon fibers is given by Young.

Electron microscopic method:
Electron microscopy is a microscopy technique whereby a beam of electrons is transmitted
through an ultra thin specimen, interacting with the specimen as it passes through. An image is
formed from the interaction of the electrons transmitted through the specimen; the image is
magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of
photographic film, or to be detected by a sensor such as a CCD camera.
Fig: Transmission electron microscope.
Electron microscopes are capable of imaging at a significantly higher resolution than light
microscopes, owing to the small de Broglie wavelength of electrons. This enables the
instrument's user to examine fine detail even as small as a single column of atoms, which is tens
of thousands times smaller than the smallest resolvable object in a light microscope. Electron
microscope forms a major analysis method in a range of scientific fields, in both physical and
biological sciences. Electron microscope find application in cancer research, virology, materials
science as well as pollution, nanotechnology, and semiconductor research. At smaller
magnifications electron microscope image contrast is due to absorption of electrons in the
material, due to the thickness and composition of the material. At higher magnifications complex
wave interactions modulate the intensity of the image, requiring expert analysis of observed
images. Alternate modes of use allow for the electron microscope to observe modulations in
chemical identity, crystal orientation, electronic structure and sample induced electron phase
shift as well as the regular absorption based imaging. Industrially, the electron microscope is
used for quality control and failure analysis.

For example, by electron microscope enables the structures to be seen more clearly and
quantitative estimates of the fibril angles of wool fiber to be made.
Fig: Electron microscope picture of transverse section of high-crimp wool.
The micro fibrils in wool are about 7 nm in diameter, packed at spacing’s of about
10 nm and separated by a matrix. However, there is a difference in structure in cells in different
parts of the fiber, as shown by the transverse section in the figure. In the meso-cortex, this is not
always easily differentiated from the para-cortex, long. Micro fibrils are packed in a hexagonal
array, which is perpendicular to the section, so that the fibrils run parallel to the fiber axis. In the
para-cortex, the fibrils are also parallel to the fiber axis, but are not as tightly and regularly
packed as in the meso cortex.
A poorly defined macro fibrilllar structure with more matrixes between macro fibrils can be seen
in the meso- and para-cortex. In the ortho-cortex, the macro fibrils appear as whorls. At the
centre the fibrils appear circular; indicating that they are perpendicular to the section, but there is
increasing elasticity at increasing distance from the centre.
This indicates that the fibrils are twisting round at increasing angles. As in a twisted continuous
filament yarn, the length of one turn of twist is constant across the macro fibril.
Conclusion:
By these methods, we can easily investigate the fiber structure which indicates the fiber
properties. We can also identify the unknown fiber. By this, we acquire vast knowledge of
investigation of fiber structure. This will help us in our future job life.

Reference
1. Class Lecture.
2. Book: Physical properties of textile fibers by W.E. Morton & J.W.S. Hearle.
3. Web sites:
http:// www.slideshare.net/abiramprince/textile-fiber-analysis-methods
http:// www.jfbi.org/.../Proceedings%20of%20TBIS%202008_2008112717
http:// www.online.physics.uiuc.edu/courses/phys598OS/fall05/...05/Nielsen.pdf
http://www. etheses.nottingham.ac.uk/2154/1/CSweetenhamThesis_final.pdf
http:// www.intechopen.com/download/pdf/27933
http://www. nopr.niscair.res.in/bitstream/.../1/IJEMS%2018(1)%2024-30.pdf
http:// www.northshorecare.com/pdf/moisture-methods.pdf
http:// www.tau.ac.il/~chenr/Pubs/katzir.pdf
http:// www1.physik.uni-greifswald.de/download/dissertationen/dr-li.pdf
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