This study attempted to introduce the bio-processes in the conventional scouring and bleaching preparation of cotton. The scouring with two types of pectinases, acting under acidic and alkaline conditions respectively, was as efficient as the chemical process in terms of obtained adequate water absorbency of the fabrics. The necessity of surfactants application in scouring was outlined. Bleaching of the fabrics was performed with hydrogen peroxide, which was enzymatically produced by glucose oxidase during oxidation of glucose. The aeration plays an important role in the enhancement of the enzyme reaction, so that the quantity of generated peroxide is sufficient to overcome the stabilizing effect of the glucose and protein in the subsequent bleaching. A closed-loop process reusing starch containing desizing baths in a single step scouring/bleaching operation with enzyme-generated peroxide was performed.
Cotton cellulose was dyed "in situ" with a polymeric dye generated by oxidative coupling of colourless 2,5-diaminobenzenesulfonic acid and 1-hydroxyphenol (catechol) with laccase. Up to 70% dye fixation was obtained increasing the concentration of catechol less soluble upon oxidation from 1 to 10 mmol, while 1 mmol of diamine was used. Dye fixation was not achieved using equal molar concentrations of the reagents.
The effect of four different enzymatic bioscouring systems for cotton have been compared in regard to the dyeability of reactive, cationic and acid dyes. The residual pectin content was determined and the results assessed in terms of dyeability against control samples prepared in the absence of enzyme. The capacity of a bifunctional reactive dye to cover the differences between fabrics treated with different bioscouring treatments was very good. Exhaustion of the cationic dye relative to alkaline scouring was increased by 27.5% and that of the acid dye decreased by 48.2%, indicating that pectin hydrolysis produced an increase in the negative charge on the fibre. The dye exhaustion differences between the four enzymatic systems studied were of significance and confirmed the hypothesis that each enzymatic system provides its own end‐groups, resulting in differences in the response of the fibre to dyeing. Enzymatic bioscouring reduces the pollution level of the effluent.
Bioscouring of cotton is normally carried out using pectinases having pectate lyase activity. The present study has examined the infl uence of pectate lyase and hydrolase on the surface of cotton fi bre. Dye uptake by cotton scoured with polygalacturonase is found to be much lower than that scoured with pectate lyase, Pectate lyase gave better dye exhaustion at 90 °C. The difference in dye exhaustion after scouring with sodium hydroxide, polygalacturonase or pectate lyase, may be due to variation in the amount of surfactant retained by the fi bre, as this hinders dye uptake. This was particularly the case with polygalacturonase. Reduced numbers of free carboxy groups on the fi bre surface could indicate lower pectin content. On the other hand it could, however, be due to the esterifi cation of carboxy groups in the pectin by hydroxy groups in the surfactant.
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