Applications of Enzymes in Textile Wet Processing
Source: New Cloth Market
Enzymes can be applied in several steps of textile wet processing and in formulation of detergent powders. Since the major textile finishing process is coloration, classical finishing processes can be divided into preparation for coloration and after-coloration steps. Coloration might be done during fibre extrusion of synthetic fibres, on a bundle of fibres, on yarns, on fabrics or on garments. The sequence of processes depends on the demands of the market for the characteristics of a final product but depends essentially at which stage the coloration process is done. (If fashion or market regulations demand materials in the raw state, they are supplied unfinished.). Preparation for coloration steps generally involves the removal of impurities, natural coloured pigments, sizes and lubricants. Preparation of synthetic fibres also involves thermal treatments for uniform dyeing. After coloration, processes include chemical and mechanical processes. Industrial laundering and home washing of garments can be also included in the after coloration processes. To give an overview of enzymatic applications in textiles a brief characterization of major wet processing steps before and after coloration and during coloration itself will be presented. Overview of traditional wet processing Preparation for coloration Enzymes can be applied in several steps of textile wet processing and in formulations of detergent powders. Preparation for coloration processes aims to prepare the textile materials to receive dyes or pigments with high fastness properties. In preparation, all impurities and natural colored pigments have to be removed. Generally preparation for coloration is similar for all colours, but is re stringent for whites and lighter des. Major processes during preparation are singeing, desizing, scouring, washing-off, bleaching, mercerising, carbonisation and thermal treatments. Singeing consists of treatment with flames to burn out fuzz fibres directly fabrics and is applied mainly on cellulosic materials and their mixtures. Desizing is the removal of sizes that are added to yarns to prevent breaks and stops during the weaving process. Desizing is only done on woven fabrics. Depending on the chemical nature of the size, removal could be effected by hydrolysis or oxidative processes or both. Scouring is the removal of natural impurities of natural fibres and can be applied to fibres, yarns, knitted or woven fabrics and garments. Scouring is done by neutral or alkaline washing with detergents. Washing-off is the removal of lubricants added during the spinning, knitting or weaving process to reduce friction and electrostatic energy. Washing-off is also done with detergents. Both the scouring and washingoff processes improve the hydrophilicity of the textile material and help the dyes to penetrate the fibres. Scouring is usually applied to natural fibres and washing-off is usually applied to synthetic fibres. Carbonisation is a process applied to wool fibres to remove the vegetal soils, by treatment with sulfuric acid. Digested cellulosic impurity residues are removed from the fibres by brushing and suction. Bleaching is the removal of naturally coloured pigments in natural fibres. Nowadays it is done with hydrogen peroxide in alkaline conditions and it applied to fibres, yarns, fabrics or garments. Bleaching treatments are performed in more gentle alkaline conditions on wool and in very caustic conditions in linen. Bleaching of bast fibres most of the time involves a double bleaching process to achieve good whiteness results. Bleaching can be combined with scouring for cellulosic knitted fabrics and combined with desizing and scouring for cellulosic wovens using more concentrated alkaline conditions where sizes and natural impurities are removed along with natural pigments. Mercerisation is the treatment of cellulosic fibres with highly...
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