Dyeing of Environmentaly Friendly Pretreated Cotton Fabric

Abstract

Raw cotton fibres have to go through several chemical processes to obtain properties suitable for further dyeing and use. With scouring, non-cellulose substances (wax, pectin, proteins, hemicelluloses...) that surround the fibre cellulose core are removed, and as a result, fibres become hydrophilic. Conventional scouring processes of cotton are conducted at temperatures up to 130 °C in a very alkaline medium (pH 10–12) with sodium hydroxide. Since a non-specific reagent is used in the treatment, it attacks impurities but it also causes damages to the cellulose portion of the fibres. Several auxiliary agents, such as wetting agents, emulsifiers and sequestering agents, which improve the efficiency of scouring and reduce the damage of fibres, are also added to the scouring bath. Scouring is regularly followed by a bleaching process, which removes the natural pigments of cotton fibres. Cellulose fibres are most frequently bleached with hydrogen peroxide resulting in high and uniform degrees of whiteness. The water absorbency also increases, however, during the decomposition of hydrogen peroxide, radicals that can damage the fibres are formed. For this reason, organic and inorganic stabilizers and sequestering agents are added to the treatment bath. Hydrogen peroxide is not ecologically disputable. The large amount of water used to rinse and neutralize the alkaline scoured and peroxide bleached textiles is ecologically disputable. Namely, the bleaching process is conducted in an alkaline bath at pH 10 to 12 and at temperatures up to 120 °C. Due to high working temperature, a large amount of energy is consumed. Auxiliary chemicals added into the bath increase the TOC and COD values of effluents. Upon neutralization of highly alkaline waste baths, large amounts of salts are produced. Consequently, the textile industry is considered one of the biggest water, energy and chemical consumers (Alaton et al., 2006; Warke & Chandrate, 2003). To comply with more and more rigorous environmental regulations and to save water and energy, biotechnology and several types of enzymes have entered the textile sector. Many review (Jayani et al., 2005; Galante et al. 2003) and scientific (Gummandi & Panda, 2003; Buchert et al., 2000) papers describe the use of different enzymes for textile finishing. Pectinases are an efficient alternative to sodium hydroxide in the removal of non-cellulose substances from the cotton fibre surface (Presa & Tavcer, 2008a; 2008b). This process occurs at moderate temperatures in a slightly acidic (Calafell & Garriga, 2004; Li & Hardin, 1998;