Novel and environmentally friendly paste-bath dyeing of protein fibers with mulberry leaf and silkworm excrement

Abstract

Silkworm excrement is one of the most important byproducts of sericulture industry. This work investigated chlorophyll and its derivatives from mulberry leaves and silkworm excrement through FTIR analysis. Thermal stability of mulberry leaves and silkworm excrement were investigated by TG and DTG. Inspired by natural mud dyeing, this work conducted eco-friendly paste-bath dyeing without extracting colorants with organic solvents. Results show that digestive enzyme and microorganism induced formation of pyropheophytins in metabolism of silkworm body is similar to those conducted through acid and/or heating, and that silkworm excrement exhibits excellent thermal stability. When used as natural dye, pyropheophytins within silkworm excrement are able to form connection with amino acid in protein fibers, at protein iso-electric point of around pH 4.8. Silk and wool fabrics dyed with silkworm excrement show deep green brown shade with satisfactory color fastness to wash and light. This work provides evidence that pyropheophytin as natural dye is more thermal and light stable than pheophytin. Functional properties such as UV protection and oxidant inhibition are also found in fabrics dyed with silkworm excrement.