Efficient Regulation of Dyeing Behavior and Physical Properties of Bombyx mori Silks via Graft Polymerization of α-Lipoic Acid

Generally, Bombyx mori silk dyeing is performed using acid dyes. However, the color fastness is always unsatisfactory due to the weak binding forces under neutral conditions. In the present work, graft polymerization of α-lipoic acid (ALA) onto silk fibers was carried out using a two-step method. Briefly, ALA was grafted onto the silk fibers, followed by a reduction-oxidation process to form poly(α-lipoic acid) (PALA) on the fiber surfaces, aiming at improving the electronegativity of fiber surface and realizing cationic dyeing. The results implied that the combined treatments promoted the intermolecular crosslinking between fibroin chains, endowing the silk fiber with low zeta potential simultaneously. A thin sedimentary layer on the fiber surfaces was observed for the PALA-deposited silk fibers, companying with a significant increase in the content of sulfur and O/N ratio, which verified the successful graft polymerization. The modified silk fabric exhibited improved dyeability, and the dyeing depth and color fastness was noticeably higher compared to that of the untreated after cationic dyeing. Meanwhile, the newly-built intermolecular disulfide crosslinks imparted a detectable anti-wrinkle effect to the silk fabric. This study provides a facile strategy for modification of silk fabric with improved dyeing behaviors and physical properties.