During the process of manufacturing, textile has to go through a long process of chemical and non chemical treatments. The Textile finishing procedure includes preparation and pretreatment, dyeing, printing and refinement of fabrics. Certain Textile Chemical
Products are highly specialized chemicals such as biocides, flame retardants, water repellents and warp sizes. Others are relatively simple chemicals or mixtures such as emulsified oils and greases, starch, sulfonated oils, waxes and some surfactants. Over sixty distinct textile chemical product classes are used in yarn formation, fabric pretreatment and finishing, textile laminating and coating, and other miscellaneous applications.
Textile Chemicals - Categories and Subcategories
From pretreatment of textile to its finishing, there are various categories and subcategories of textile chemicals :
scouring agents, low foam scouring agents, wetting agents, low foam wetting agents, sequestering agents, mercerising agents, peroxide stabilisers, peroxide killers, neutralizers
Textile Dyeing Chemicals
Solubalisers & dispersents, levelling agents, soaping agents, dyeing agents.
Dyeing & Printing Chemicals
vat levelling agents, thickners, binders, stain removers, anti back staining agents
cationic softners flakes/ paste, nonionic softners flakes/ paste, anionic softners flakes/ paste, reactive softners, cold water soluble softner flakes
spin finishes, spining aids
Other Speciality Chemicals.
Chemical Based Procedures of Textile Manufacturing
Various processes are carried by the textile production units where different chemicals find their usage. These processes include, Scouring, Bleaching, Desizing, Softening, Mercerization, Dyeing, etc.
Raw textile materials, in their natural form,haveadditives, dirt, soil and other impurities that are not suitable for clothing materials. Pesticides, fungicides, worm killers, etc are also there in these raw materials. The removal of these matters is called scouring. It is done by adding suitable wetting agents, alkali or other chemical or non chemical materials. After scouring, the fabric gives better wetting and penetration properties. This makes the subsequent bleach process easy resulting in better dye uptake.
If cloth is to be finished white or is to be given serface ornamentation, all natural colours must be removed. This process of decolorization of raw textile material is bleaching. Bleaching is classified in to oxidative bleaching and reductive bleaching. Generally oxidative bleaching is carried out using sodium hypochlorite, sodium chlorite or hydrogen peroxide. Natural fibres
like cotton, ramie, jute, wool, bamboo are all generally bleached with oxidative methods. Reductive method of bleaching is done with Sodium hydrosulphite, a powerful reducing agent. Fibers like Polyamide, Polyacrylics and Polyacetates are generally bleached using reductive bleaching technology. After scouring and bleaching, Optical Brightening Agents (OBA), avaialable in different tints such as blue, violet and red, are applied to give the textile material a brilliant white look.
Bleach Clean up
Bleaches are highly reactive chemicals and any such chemicals left on the fabric can hinder the process of dyeing. Thus cleaning of bleach is also done. The bleach is neutralized with a precisely controlled reducing agent.
During weaving, specially for the fabrics made from cotton or blends, the warp threads are coated with an adhesive substance known as 'size'. This is done to prevent the threads from breaking during weaving. Starch and its derivatives are the most common sizing agents. After weaving, the 'size' is removed again in order to prepare the fabric for dyeing and finishing. This is called Desizing. It is done by treating the fabric with chemicals such as acids, alkali or oxidising agents.
Fabric softener also called Fabric Conditioner is used to prevent static cling and make fabric softer. Their use may however reduce the water absorption capabilities of the fabric. Fabric softeners work by coating the surface of the cloth fibers with a thin layer of chemicals. These chemicals have lubricant properties and are electrically conductive, resulting in smoother feel and preventing the buildup of static electricity. It also increases resistance to stains and reduces wrinkling.
In this process, textiles (typically cotton) are treated with a caustic solution for improving properties such as fiber strength, shrinkage resistance, luster, and dye affinity. Higher-end fabrics may be double or triple mercerized for added benefits. The treatment consists of dipping the yarn or fibre in a solution of sodium hydroxide and then treating the material with water or acid to neutralize the sodium hydroxide.
While dyeing, large volume of dyestuff, thickening agent and small amount of water are used. Many textile chemicals like Dispersing agent, Leveling agent, Acid buffer etc are used during the process. The dyestuff have to be either fermented (for natural dye) or chemically reduced ( for synthetic vat and sulfur dyes) before being applied. This makes the dye soluble so that it can be absorbed by the fiber. Direct dyes are water soluble and can be applied directly to the fiber from an aqueous solution. Most other classes of synthetic dyes, other than vat and sulfur dyes, are also applied in this way.
decorates fabric by imparting colours which can further be enhanced by printing colour designs on the finished cloths. Many kinds of dyes are used for printing including vat, reactive, naphthol, disperse and pigment colours among others. These are fixed to the fiber by means of resins. Sometimes cheap prints are also made with basic colours mixed with tartar emetic and tannic acid. Silk is usually printed with acid colours. Wool is treated with chlorine to make it more receptive to colours and to prevent shrinking and is printed with acid or chrome dyes. Fabics made of synthetic fibers are generally printed with disperse and cationic dyes.
Problems in Finishing Processes and their Solutions
It has been found that 70% of the problems in finishing processes are due to poor treatment of the fabric. Thus it becomes essential to give emphasis on right kind of chemicals and process control parameters right from pretreatment to ultimate dyeing and printing steps for getting best finished textile.
Some of the faults due to poor pretreatment can be listed as poor absorbency, catalytic damage or poor fluidity, stains , Moire effect, shade change from selvedge to selvedge, shrinkage/distortion, creasing/chafe marks, inferior brightness/luster, cloudy dyeing, skitteriness, pale areas, darkspots, ropemarks etc. Most of these faults can be easily corrected with certain precautions like use of specialty chemicals, suitable heat setting temperatures, thorough relaxation of the material, controlled tension and uniformity of batching during pretreatment and checking for rough patches in the machine.
While dyeing, selection of dyes with better dispersion stability, use of efficient dispersants, controlled heating when the dye exhibits a particularly high rate of exhaustion, use of anti foamers and special chemicals like welting agent or defoamer combinations etc. can give the best results.