Introduction lecture 1

INTRODUCTION TO WET PROCESSING
LECTURE - 1
By Robel L.
Faculty of Textile and Fashion Technology
Aksum University
2020
2/20/2020 1

TEXTILE WET PROCESSING
 There is far more to go after fabric production to make the
substrates suitable for end-use and hence satisfy customer
requirements.
 The substrates lack attractiveness or aesthetics and serviceability or
adequate performance which are required for their effective
utilization.
 Attractiveness and improvement of properties are achieved through
pretreatment, coloration and finishing of the textile materials.
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Pretreatment Coloration Finishing
Pretreatment: Removal of impurities for smooth chemical processing
Coloration: Application of color using dyes/pigments for attractiveness
Finishing: Improvement of end use property by applying finishes
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PRETREATMENT OF TEXTILE MATERIALS
 Grey goods are contaminated with impurities
 Cellulosic fibers (cotton) contain various impurities: fats, waxes,
protineous matters, etc.
 Wool fiber contains wool wax (grease), inorganic salts and other dirt
matters.
 The serecin gum in silk fiber is also considered as impurity.
 Synthetic fibers such as polyester and nylon are contaminated with
spin finish lubricants.
 Besides inherent fiber impurities textile substrates are contaminated
with added impurities which are used in facilitating the conversion
process from fiber to fabric.
 These include size and lubrication oils.
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What is the fiber forming polymer of cotton, wool, silk
polyester and nylon?

5
Pretreatment process of textile material are:
 SINGEING: Burning of protruding fibers
 DESIZING: Removal of size material
 SCOURING: Removal of oil and wax based impurities
 BLEACHING: Removal of coloring matters
 MERCERIZATION: Treatment with caustic soda for value addition
 CARBONIZING: Removal of vegetable matters in wool fiber
 DEGUMMING: Removal of silk gum in silk fiber
cont...

Cotton fiber composition
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Composition of cotton
Natural impurities
Constituent %
Cellulose 88
Waxes 0.5
Pectins 0.7
Proteins 1.1
Coloring matter 0.5
Mineral Matter 1.0
Moisture 8.0
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Fats and Waxes
Fats are Triglycerides of fatty acids
FATS CAN BE EASILY SAPONIFIED BY NaOH INTO SOAPAND GLYCEROL
Stearic acid
Waxes are (Esters of fatty alcohol)
C17H35COOH + C28H57OH = C17H35COOC28H57
Stearic acid Montanyl alcohol
WAXES ARE DIFFICULT TO SAPONIFY BY ALKALI
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FATTYACIDS AND FATTYALCOHOLS FOUND IN COTTON FIBRE
Fatty acids
 Stearic acid
 Palmitic acid
 Oleic acid
Fatty alcohols
 Gossipyl alcohol (C30H61OH)
 Ceryl alcohol (C26H53OH)
 Montanyl alcohol (C28H57OH)
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Pectins
 Derivatives of pectic acid
 Polymer of high molecular weight
 Composed of Galactouronic acid
 Some COOH groups are present as Ca and Mg salts
 Free acid and Ca and Mg salts are insoluble in water
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Proteins
 Nitrogenous compounds
 Present in primary wall and Lumen
 Some of the amino acids identified are
Leucine
Valine
Proline
Alanine etc.
 Yellowish (Creamish) colour of cotton is related to Proteins and
Coloring matter
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Coloring matter
 Color pigments present are
 3,5,7,2’, 4’ Penta hydroxy flavone (Morrin)
 3,5,7,8,3’,4’ Hexa hydroxy flavone (Gossypetine)
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Added Impurities
Sizing agents:
 Agents used to give protective coating to warp threads
 Minimize the breaking of warp threads during weaving
 Improve weaving productivity.
 The operation is known as sizing.
 Starch is one of the most important sizing agent for cotton
 Sizing agents and
 Oil stains
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 Inhibit penetration of chemicals used in coloration/finishing
 Interfere with coloration/finishing processes
 Reduce the visual appearance of textiles
 Unless the impurities are removed subsequent chemical
processing can not be smoothly accomplished.
 A procedure mainly concerned with the removal of natural
as well as added impurities in fabric to a level necessary
for good absorbency and whiteness by utilizing minimum
time, energy and chemicals as well as water.
Influence of impurity
Chemical Pretreatment
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PREPARATION BEFORE PRETREATMENT
Inspection
 The most important point is to obtain fabrics "free from exterior impurities" in
order to achieve smooth and trouble free results in the subsequent finishing
systems
 It is checked whether the grey fabrics are in conformity with standards, and all
weaving faults are marked out.
Mechanical cleaning of fabric
 Brushing to remove the short and loose fibers from the surface of the cloth.
 Shearing is cutting of the loose strands of fibers from fabric with a sharp
edged razor or scissors.
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Principles of Brushing
 Fabric moves in contact with Cylinders (2-4) covered with fine
bristles (Brush Roller).
 The loose threads are picked up by the brush rollers.
 Removed by vacuum.
 In this operation only loose threads are removed
 Threads attached to the fabric surface removed by shearing/cropping
operation.
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Principles of Cropping
 Achieved by raising the loose thread with the help of brush
roller and cutting it close to the fabric surface with the help of
spiral blades.
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Purposes of Preparatory Processes
To remove Natural and added impurities
To impart certain desirable properties (water absorbency)
To improve the appearance of fabric (whiteness)
To make it suitable for subsequent processes like dyeing,
printing finishing
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Principle of preparatory processes
 The impurity are insoluble in water
 Conversion of water insoluble impurities to water soluble form.
 Chemical reactions involved (In case of Cotton)
 Hydrolysis
 Oxidation
 The choice of chemicals depends on chemical nature of
impurity.
2/20/2020 19

Introduction lecture 1

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