This document provides an introduction to wet processing of textiles. It discusses that fabrics require pretreatment, coloring, and finishing to make them suitable for end use by improving aesthetics and properties. Pretreatment involves removing impurities through processes like singeing, desizing, scouring, bleaching, and carbonizing. This allows for smooth coloring and finishing. The document outlines the natural impurities in cotton like fats, waxes, pectins, proteins, and minerals, as well as added sizes and oils. It explains that pretreatment converts insoluble impurities into water-soluble forms through chemical reactions like hydrolysis and oxidation.

1. INTRODUCTION TO WET PROCESSING
LECTURE - 1
By Robel L.
Faculty of Textile and Fashion Technology
Aksum University
2020
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2. 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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3. 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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4. 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. 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...

6. Cotton fiber composition
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7. 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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8. 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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9. 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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10. 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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11. 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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12. 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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13. 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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14.  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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15. 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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16. 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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17. 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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18. 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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19. 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.
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20. END
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