Laccase-catalyzed enzymatic dyeing of cotton fabrics

As some synthetic dyes are regarded to be toxic, mutagenic and carcinogenic, the search for eco-friendly alternatives for the synthesis of dyes and coloration has gained importance. For this reason, this study focused on finding new eco-friendly alternatives for coloring cotton. 100% cotton knitted fabrics were subjected to enzymatic coloration using a commercial laccase enzyme and various precursors. After determining the colors, the effect of pH on the enzymatic dyeing process was investigated. Then the optimization of reaction conditions was also realized statistically for the precursors giving the best results in terms of color. With the aim of obtaining further improvements in color-yield values obtained in enzymatic dyeings, the effect of the pretreatment process and the use of ultrasound were also investigated. Furthermore, the reaction pathways in enzymatic coloration were explained and results were confirmed by means of Fourier Transformed Infrared analysis. As a result of experimental studies, red and lilac colors could be successfully obtained on cotton for the first time in the literature. In this way, the theoretical basis of enzymatic dye synthesis and dyeing of cotton was clarified comprehensively. Furthermore, technical (color reproducibility; washing, rubbing, light and perspiration-fastness values; and UV protection factor), economical (chemical, energy and water consumption required for dyeing (including aftertreatments) of 1 kg fabric) and ecological aspects of enzymatic dyeings were compared with reactive dyeing. According to the experimental results it was found that biological treatment alone was enough for wastewater of enzymatic coloring, while chemical treatment will also be needed in reactive dyeing wastewater. Furthermore, color reproducibility, evenness and UV protection properties of dyed samples were comparable with that of reactive dyeings. However, in terms of the fastness levels achieved, the enzymatic coloring was far behind the reactive dyeing.