Basic Research On The Application Of Green Processing Of Silk Fibers

Silk(derived from bombyx mori cocoon) is a natural protein fiber,which is reputed as“queen of fibers”for its unique mechanical properties,heat resistance,insulating properties,moisture absorption as well as special lustre.Silk is not only widely used in the textile field,but also has been appliedinmany other fields such asbiomedical,food,cosmetics and industrial supplies for its excellent natural properties such as biocompatibility,controllable degradability and environmental stability.However,due to the limitation of technical level or other reasons,there are some problems in the silk processing,such as a low degree of green processing and a decrease in the naturalness of silk products.Especically,silk degumming(refining)and chemical weighting are of universal concerned.In order to make better use of silk fibers and improve the green degree of silk processing,in this paper,a series of basic research on the silk processing has been carried out with the purposes to provide theoretical and experimental basis for the green processing of silk fibers.The contents and results of this study are as follows:(1)In order to overcome the problems that a lot of chemical reagents such as acid and alkali are introduced in the current silk degumming(refining)process,and the removed sericin cannot be effectively used,raw silk fibers were treated with steam,and the effect of treatment time on the morphology and performance of silk fibers was studied.Results show that,steam treatment can change the hydrogen bonds inside the fiber molecules,make sericin fall off from the silk fibroin;Steam treatment in a proper temperature and time(125?,0.14 MPa,90 min) could remove sericin,however,the crystalline structure and mechanical properties of silk were not affected,suggesting the feasibility ofsilk degumming with steam.Meanwhile,since no chemical reagents were introduced in the steam treatment,the recycle of sericin becomes simple and easy,making it an environmentally friendly degumming method.(2)Based on the difference of physicochemical properties of chemically grafted silk and natural silk,the two kinds of fibers were dissolved in concentrated acid,and the detection method for fast and effective identification of chemically grafted silk wadding was explored according to the different color phenomena of the two kinds of silk fibers in concentrated acid(concentrated HCl and concentrated H₃PO₄).The results showed that the blue-purple reaction of natural silk dissolved in concentrated HCl was caused by tryptophan and tyrosine,and the oxidation modification of the two amino acids would hinder the formation of blue-purple pigment.Since the two amino acids of silk will be destroyed by oxidation in the process of grafting,this chromogenic reaction can be used to detect whether silk is chemically grafted or not.This identification method has been applied to relevant industry standards of silk quilt.(3)Silk fibroin powder is another utilization form of silk fibers.Inspired by the investigation of steam degumming,silk fibroin fibers(degummed by steam)were treated with steam combined with low-concentration sodium carbonate solution(Na₂CO₃)to prepare silk fibroin powder.Results showed that with the treatment of high temperature Na₂CO₃ solution,silk filament gradually breaks up into loose short fiber and becomes soluble.Soluble and insoluble silk fibroin powder can be obtained with this method,and the molecular weight of silk fibroin powder can be regulated by adjusting the concentration of sodium solution.Compared with the traditional ternary system(high concentration ethanol-CaCl₂-aqueous solvent)preparation method,this method is simple and dose not introduce a large amount of chemical reagents.Besides,low content of Na₂CO₃ is used,and the dialysis solution can be reused.Sometimes time-consuming dialysis can be omitted where purity is not critical,therefore,this low sodium salt silk powder preparation method has a positive effect on reducing environmental pollution and saving production costs.(4)The morphology and properties of sericin that obtained from steam degumming immobilized by chitosan were studied,and its adsorption effect on Cu(?) was also evaluated.The effects of sericin with different molecular weight distribution on its immobilization were investigated and the corresponding immobilization methods were established.The physicochemical properties of the immobilized sericin were characterized,and its static adsorption properties on Cu(?) was investigated.The results showed that the molecular weight distribution would affect the forming effect of sericin.High molecular weight sericin(?245 kDa)should be immobilized by embedding-crosslinking with chitosan,while low molecular weight sericin(?75 kDa)should be immobilized by pre-crosslinking with appropriate crosslinking agent after blending with chitosan.In the static adsorption experiment of Cu(?),the higher sericin loaded,the better the adsorption effect for Cu(?).When the pH value is around 4-5,the adsorption effect is ideal and a faster adsorption kinetic process was presented,which conforms to the pseudo-second-order kinetic model.In addition,the immobilized sericin was subjected to five cycles of adsorption-desorption experiments,which shows that it had an ideal recyclability and could be used for purification of Cu(?)-containing wastewater.