Trichoderma reesei cellulases in processing of cotton: Dissertation

Today the use of enzymes in textile processing and after-care is already well established industrial technology. Enzymatic process applications have increased substantially due to developments in genetic engineering, as specific enzymes can be efficiently modified for targeted applications. In addition, being biological molecules and efficient catalysts, enzymes can provide environmentally acceptable routes to replace harsh chemicals. Furthermore enzymatic processes can be applied using equipment already existing in the textile industry. The cellulases of the soft-rot fungus Trichoderma reesei are the most studied and understood of all cellulolytic systems. Cellulases are used for modification of cellulosic fibres and fabrics, e.g. cotton, viscose and lyocell, yielding properties such as stonewashing, peach-skin and biofinishing effects. Cellulases are usually applied as multi-component enzyme systems and most of the commercial cellulases contain a variety of different activities. The cellulolytic system of T. reesei is composed of two cellobiohydrolases (CBHI and CBHII), at least six endoglucanases and two ß-glucosidases. Cellulases are known to act synergistically in the hydrolysis of crystalline cellulose. Endoglucanases randomly attack the amorphous regions in cellulosic substrates, whereas cellobiohydrolases can also act the crystalline regions of cellulose, releasing cellobiose from the ends of cellulose chain. In the present investigation, purified T. reesei cellulases CBHI, CBHII, EGI and EG II were used to treat different types of cotton fabrics in order to evaluate the effects of individual mono-component cellulases on cotton properties. By comparing the impact of mono-component cellulases on cotton twill and poplin woven fabrics and interlock knitted fabric, it became apparent that cellobiohydrolases and endoglucanases have different effects on the tested fabrics. CBHII did not have any pronounced effect on cotton. By contrast CBHI produced significant amounts of reducing sugars and caused weight loss of fabrics. When a high hydrolysis degree was used, i.e. the weight loss was pronounced, EGII caused more strength loss than either EGI or CBHs. By limiting the treatment time and using additional mechanical action it was observed that EGII was able to improve the pilling properties of cotton fabrics even at low weight and strength loss levels. In addition, the possible synergistic effects between different cellulases were evaluated with different ratios of endo- and exoglucanases. According to weight loss and reducing sugar analyses, both endoglucanases exhibited clear synergism with CBHI. EGI also showed slight synergism with CBHII. Practically no endo-endo or exo-exo synergism was observed on the basis of weight loss analysis. Compared to cellulase mixtures, the EGII treatment alone improved the pilling resistance more and resulted in less weight and strength losses at the same protein dosages. Thus, there was no correlation between high weight loss and good pilling results. On the basis of the knowledge obtained from the mono-component treatments, new cellulase preparations with different profiles of T. reesei cellulases were developed. Using these experimental cellulases, it was found that high pilling removal was dependent on the fabric type, and again EGII-based cellulase products yielded the most positive depilling results. It was also shown that the strength loss could be minimized by having only EGII present in the cellulase mixture. The effects of the purified endoglucanases and cellobiohydrolases and an experimental cellulase mixture on denim were also evaluated. The results confirmed that endoglucanases are the cellulases required for a good stone washing effect, and EGII was the most effective in removing color from denim despite a very low hydrolysis level. CBHI did not produce any stone washing effect. When the impact of purified cellulases on the molecular weight distribution of cotton powder obtained after enzyme treatment was studied, EGII was the only enzyme which reduced the molecular weight of cotton powder with high mechanical action. The results also showed that mechanical agitation affected the performance of EGII more than that of EGI measured as weight loss and molecular weight of cotton powder.