Fixation of the Color of Naturally Colored Domestic Silk by Cross-Linking the Sericin with Tetrakis (Hydroxymethyl) Phosphonium Sulfate

The pigment of naturally colored domestic silk (NCDS) is present in the sericin layer rather than in the silk fibroin, and the color losses easily during the wet process accompanied by dissolution of the sericin. In this study, the sericin of naturally colored domestic silk was cross-linked to a water-insoluble network via treatment with a hydroxyalkyl phosphine compound, tetrakis (hydroxymethyl) phosphonium sulfate (THPS). The effects of reaction conditions, such as pH, reagent concentration, reaction temperature, and time on the cross-linking effect were investigated. Cross-linking the NCDS samples at a relatively good condition could decrease the weight loss from initial 16.7 % to less than 4.5 % during degumming. The cross-linked NCDS showed a K/S value (color depth) 1.84 times higher than the uncross-linked sample after 20 cycles of washing. The method for fixing the color of NCDS offers a kind of solution with high practicality and low cost. The cross-linker proposed in this study could also be an alternative for cross-linking sericin based materials.