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Introduction to Textile Preparation

Assistant Professor Dr. Apichart Sonthisombat, Rajamangala Institute of Technology

Copyright © 2 0 0 4 Assist. Prof. Dr . A. Sonthisombat All rights reserved.

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Basic Textile DefinitionsFibers = A smallest unit of textile materials. Usually classified by flexibility, fineness, and a ratio between length and diameter (L/D ratio)Natural Fibers = Fibers that come from animals (wool, silk etc.), plants (cotton, flax, hemp, jute etc.) or mineral material(asbestos).Synthetic Fibers = Man-made fibers or artificial fibers which is usually comes from chemical agents.

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Semi-synthetic Fibers = Fibers that comes from solutions of natural polymer or derivatives from the natural polymer (cellulose, protein etc.)Polymer = Macro molecules containing small chemical units (named “Monomer”)

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Staple Fibers = Fibers from natural or synthetic fibers which were cut into short fibers. Normally, natural fibers are staple fibers (expected silk fibers). These fibers have 5-500 millimeters long.Filament Fibers = Fibers from natural or synthetic fibers which have infinite length. Silk Fibers are the only one natural fibers classified in this definition since their length between 700-1500 meters depending to their races.

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Yarns = The combinations of fibers using some twisting (Z and S twists) in order to make strong and stable yarns.Spun Yarns = The yarns that come form staple fibers.Filament Yarns = The yarns that come from filament fibers (mono-filaments and multi-filaments)Fabrics = The products of weaving, knitting or non-woven processes. Normally, fabrics have a certain thickness and can withstand tear and tensile forces.

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Textile Preparation is the heart of the textile dyeing, printing and finishing processes because fibers, yarns or fabrics have many impurities (i.e. cotton wax, starch, lubricant, silk sericin, wool oil etc.) as a proverb “Well begin is half done”. From the experience, more than 60% of the faults from these factories come from preparation.

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The Examples of preparation processes of cotton and its blends fabrics

100% Cotton fabrics

1. Singeing

2. Desizing (only for woven fabrics)

3. Scouring

4. Bleaching (only for pale or bright shades)

5. Mercerizing

6. Adding of Optical Brightening Agent

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100% Silk Fibers

1. Degumming (to get rid of non-fibrous materials (sericin))

2. Bleaching (to make the goods whiter)

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100% Wool Fibers

1. Carbonising (to remove leave, bark and other parts of the plants from the wool fibers)

2. Scouring (to get rid of fat and oil from the fibers)

3. Bleaching (to make the fibers whiter)

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Morphology of Textile Fibers1. Crystalline Regions are the regions that cannot absorb water, humidity and dyestuff solutions but they are the part for fiber strength.2. Non-Crystalline Regions or Amorphous regions are the regions that can absorb water, humidity and dyestuff therefore they can be dyed but they are a very weak part of the fibers.

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3. Orientation of the Crystalline Regions alongside the fiber axisThis property is very important in that it will increase the tensile strength of the fiber if it presents in the optimal quantity.

Crystalline

Amorphous Void space

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Singeing ProcessSingeing is a process that uses gas flame or hot plate in order to get rid of small fibers protruding (hairs) on the fabrics (these fibers normally come from spun yarns).Objectives:1. To get rid of the small fibers2. To make the fabrics smoother than before3. To help the printing ink or dyestuff to make clearer marks on the fabrics4. To improve rubbing fastness and washing fastness of the dyed or printed fabrics

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Where does starch come from?Starch or Size is a material that help the weavers to ensure that their warp yarns are not broken or struggle with the reeds. Therefore these will leading to low productivity and high machine break-down rate.

Desizing processThis will get rid of the starch or size covering the warp yarns using enzymes, oxidizing agent, or other chemicals.

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As the starch or size covering the warp yarns, it will lead to uneven dyeing, printing or finishing. No need for this material on our fabrics. (Note this will effect only weaving process. For knitting process, no starch or size on the fabrics thus no need to desizing.)Objectives1. To get rid of starch from sizing of the warp yarns2. To ensure levelness of the dyestuff or printing ink. If not taken out completely, it will affect washing and rubbing fastness of the fabrics.

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Scouring ProcessScouring process is a process designed to remove natural fat, wax, oil from the cotton fabrics using sodium hydroxide and detergent at boil for 20-30 minutes. Synthetic fabrics and other protein fabrics may use only sodium carbonate (weaker alkali) instead.

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Objectives1. To remove natural fat, wax, and oil materials containing in the fabrics without damaging the fibers2. To accelerate dye and chemical absorption of the fabrics3. To improve the handle of the goods (softer)

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Bleaching ProcessThe process is to make the goods whiter than before. This will help the goods to absorb more dyes and chemical and also make the dye on the goods brighter. Normally, for cotton fabrics, hydrogen peroxide in alkali solution at boil are the most popular bleaching agent.Objectives1. To whiten the goods2. To make the goods to be suitable for dyeing and printing with pale or bright shade3. To be follow with adding optical brightening agent process (super white)

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Mercerizing ProcessThe is to make the cotton goods more luster than before using sodium hydroxide solution in cold condition and tension. This will lead the cotton fibers to be swollen and increased strength. Also this will improve dye absorption of the fibers. John Mercer was the first chemist in the world who found this phenomenon in 1844. Therefore, the process was called “Mercerizing”Caustizing is the process nearly the same as mercerizing but it uses lower concentration of the hydroxide solution and without tension.

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Objectives1. To make the goods more luster because raw cotton fibers are ribbon-like. After this process, the fibers change to cylindrical shape resulting more evenness reflected light from the goods.

Before After2. To improve dyeability of the goods about 5-10%.

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Adding Optical Brightening AgentThe process is to add special dyestuff into textile or paper to make them brighter when looking at black-light light bulb or natural sunlight. As the dyestuffs are colorless but using UV light to excite these dyes. They will reflect the light at the wavelength that human can see (i.e. blue, violet). So the goods look brighter and whiter.

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