Using of hydrated lime water as a novel degumming agent of silk and sericin recycling from wastewater

Abstract

The aqueous solution of hydrated lime (calcium hydroxide) was first used as a silk-degumming/refining agent. The sericin outside silk fibroin filaments was completely removed after boiling (20 min × 2) in a 0.025% calcium hydroxide solution. The calcium hydroxide degumming did not induce an evident breakage of the silk fibroin peptide chains. The tensile, thermal and surface properties of the fibroin fibre all showed that it is a degumming agent slightly low to neutral soap and far superior to Na2CO3 solution. The alkaline degumming wastewater containing sericin was neutralized by sulphuric acid or phosphoric acid and generated insoluble calcium salt precipitation, which can be used as plant fertilizer. After the residual solution was concentrated and filtered, the sericin powder was obtained using a spray dryer or lyophilizer. The sericin with a lower molecular mass (≤20 kDa) can be widely used in such applications as cosmetics, medical biomaterials, food or medium additives. The hydrated lime water as a novel silk degumming agent can be used widely in the silk industry. The degumming technology not only avoids serious environmental pollution from degumming waste liquid, but also can recover a large number of biological resources-sericin protein.