Superheated water hydrolyses of waste silkworm pupae protein hydrolysate: A novel application for natural dyeing of silk fabric

A large amount of by products are generated during the silk processing, the most abundant of which are silkworm pupae. In general, efforts have been made to use these by-products for different applications such as biogas, fertilizer, human food products, medicines and pupa oil production. In this work a novel application of protein extracted from silkworm pupae was proposed for the coloration of silk fabrics within the context of the circular economy. In particular, for the first time a hydrolysis process at 170 °C for 1 h using only superheated water was performed to extract proteins from silkworm pupae and as a novelty, the same proteins were used to dye silk fabrics. Various parameters such as temperature, time, pH, dyeing time and temperature, protein hydrolysate concentration, mordant type (copper sulfate and ferrous sulfate) and mordanting step (pre-meta-post) were studied and the higher color strength was obtained at pH 3.8, 90 °C, for 60 min dyeing time using 30% o.w.f. protein hydrolysate, 50% o.w.f meta-mordanting. It was demonstrated that the extracted proteins can actually dye, but the color is more intense in the presence of the mordant which plays an anchoring role by formation of complex between protein hydrolysate and silk fabric. Dyed fabrics in the presence of mordant show washing and rubbing fastness from good to excellent, and light fastness from fair to good.