| Silk is mainly composed of silk fibroin and sericin.It is well known that sericin surrounding natural fibroin fibres is partly removed in the silk reeling industry to obtain raw silk,a textile stock.Sericin surrounding the fibres is fully removed in the refining/scouring of raw silk,the manufacture of silk floss quilts,or the development of biomedical materials.Generally,the separation of silk fibroin and sericin is an important process and is known as degumming in the laboratory or refining/scouring in silk industry.However,the sericin protein is difficult to be recovered or reused from the degumming waste.The degumming of silk or raw silk in the silk textile industry and the manufacture of silk floss quilts not only used alkaline salts similar to Na2CO3(such as NaHCO3 and sodium silicate)as refining/scouring agents but also supplemented bleach and softening agents,which are necessary to enhance silk fibre,making it smooth,soft,and shiny.Currently,separating and recovering sericin from a large amount of refining/scouring alkaline waste is quite difficult to perform because of the substances used in the degumming process.Therefore,developing a new environment-friendly silk degumming agent is very important for silk processing as well as the recovery and utilization of sericin.Presently,a nonionic and efficient surfactant alkyl polyglycoside(APG)has been widely applied in many areas,such as an industrial detergent[4],for drug delivery[5],and in agrochemistry,[6,7]due to its green and environmentally friendly characteristics.The aqueous solution of Ca(OH)2 is commonly known as hydrated lime water.Aqueous Ca(OH)2 solution became one of the most commonly used and cheapest sericulture disinfectants.Here,we first used APG and Ca(OH)2 as a silk degumming agent for the degumming test of silk or silkworm cocoon.Alkyl polyglycoside(APG),a nonionic surfactant,is often considered to be a green surfactant and is synthesized using glucose and long chain fatty alcohols.It is used as a degumming agent of Bombyx mori silk fibre in this study for the first time.We studied APG systematically in comparison to the traditional degumming methods.such as aqueous solutions of sodium carbonate(Na2CO3)and neutral soap(NS).After repeatedly boiling silk fibres in an aqueous solution of 0.25%APG three times for 30 min and using a bath ratio of 1:90-120(g/mL),sericin was completely removed from the fibre.SDS-PAGE showed that the degumming in APG did not induce an evident breakage of the silk fibroin peptide chains.including the light chain and P25 protein.The tensile properties,thermal analysis,and scanning electron microscopic(SEM)observation of the degummed fibroin fibre all show that APG is a degumming agent similar to NS and far superior to Na2CO3.These results indicate that APG is an environment-friendly silk degumming/refining agent in the silk textile industry and in the manufacture of silk floss quilts.Quicklime,which is commonly known as calcium oxide(CaO),is an oxide generated by limestone/marble after calcination at high temperature(its main component is calcium carbonate CaCO3).When quicklime reacts with water,hydrated lime is generated,which is known as slaked lime.Hydrated lime is referred to as calcium hydroxide(Ca(OH)2),which is a type of slightly water-soluble white powder.The aqueous solution of Ca(OH)2 is commonly known as hydrated lime water.In early times,this solution was often used to disinfect silkworm-rearing instrument and room to prevent the occurrence of all types of silkworm diseases and pathogen contamination.Hence,aqueous Ca(OH)2 solution became one of the most commonly used and cheapest sericulture disinfectants.Hydrated lime or calcium hydroxide is a type of strong base,as well as sodium hydroxide,but the difference is lower solubility of hydrated lime in water,and the solubility decreases with increasing temperature.The aqueous solution of hydrated lime(calcium hydroxide,shortly Ca(OH)2 was first used as a silk-degumming/refining agent,which provides a green technology to treat the wastewater and recycle edible sericin.The sericin outside silk fibroin filaments was completely removed after double boiling(20 min X 2)in a 0.025%Ca(OH)2 solution,in which the silk-degumming rate approached 28%.The degummed silk fibroin filaments were slightly damaged so that the original mechanical properties were basically maintained.The alkaline wastewater containing sericin was neutralized by sulphuric acid and generated insoluble calcium salt precipitation(CaSO4)used as plant fertilizer.After the residual solution was concentrated and filtered,the sericin powder was obtained using a spray dryer.The sericin with a lower molecular mass(?20 kDa)can be widely used in such applications as cosmetics,medical tissue engineering materials,and food or medium additives.Therefore,Ca(OH)2 is an environmentally friendly silk-degumming agent.All generated sericin and calcium salt can be efficiently recycled.In this paper,green nonionic surfactants-APG and Ca(OH)2 aqueous solution as two environmentally friendly,sustainable silk refining/degumming agent,were used in a series of silk degumming or refined processing technology such as cocoon and silk degumming,raw silk scouring,silk spinning scouring,silk scent and other technology.In particular,the using of Ca(OH)2 aqueous solution as a silk degumming/refining agent,which produces a large number of sericin-containing alkaline waste by adding sulfuric acid or phosphoric acid,make us reach the goal of recycling the whole sericin and calcium salt precipitation,thus avoiding the traditional alkaline degumming waste liquid on the environment serious pollution.This article provides two new methods for silk industry,especially silk degumming and refining,to provide new hope for the sustainable development of silkworm industry. |
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