Mechanism and Analysis of Laccase-mediated Coloration of Silk Fabrics

Laccase provides a mild and eco-friendly alternative for the dyeing of fabrics. In this study, laccase-mediated catalytic oxidation was employed in coloration of silk fabrics, and the color was then assessed. The surfaces of silk fabrics were characterized by scanning electron microscope (SEM), atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). Their thermal and crystallization properties were also investigated by differential scanning calorimetry (DSC), thermogravimetry (TG), and Xray diffraction (XRD). The textile softness was evaluated by the bending rigidity (B). In addition, high performance liquid chromatography (HPLC) and ultraviolet-visible (UV-VIS) spectroscopy were employed to analyze hydrolysate of silk fabrics obtained from hydrolysis with hydrochloric acid solution. The results demonstrated that a stable reddish-yellow layer was formed on the surface of silk fabrics by the laccase-mediated coupling of phenol hydroxyl side chains in the silk polypeptide. Moreover, the SEM and AFM observations showed that the surface of colored silk fiber was slick. ATR-FTIR and XPS results demonstrated differences in the C, N, O contents and the functional groups of the uncolored and colored silk fabrics. The DSC, TG, and XRD indicated that the thermal properties of silk fabrics were not affected by laccase and the coupling reaction mainly occurred in the amorphous region. The DMF extraction test further illustrated that covalent bonds were formed between tyrosine residues constituent of silk peptides. Finally, HPLC and UV-VIS results showed that new substances were formed as a result of conjugation between benzene rings.