Processing Improvement Of Machine-drawn Silk Sheet, By-product Recovery And Their Application In Amino Acid-based Surfactant

The objective of this study was to improve the present silk floss processingtechnology, besides the efficient recovery of sericin, and the application of itsbyproducts on amino acid-based surfactant. Firstly, we improved the hot watercirculation leaching system, silkworm (Bombyx mori) cocoons especially twin cocoonswere quickly reeled into a raw silk sheet with cycled hot alkaline eluent in a processingmachine at50~60oC, and the alkaline eluent was replaced by the newly prepared afterseveral times silk floss processing. Secondly, we improved the traditional scouringprocedure of machine-drawn raw silk sheet. The raw silk sheet was refined in stronglyalkaline electrolyzed water (SAEW, pH≥11.5) for0.5h before the traditional scouringprocedure, and large amount of alkaline SAEW scouring solution containing sericin wasobtained. Then, the crude silk sheet was treated by the boiling traditional scouring agent(without alkaline compounds). Finally, the crude silk sheet was repeatedly washed withwater, followed by dewatering and drying. The pale and soft refined silk floss(degummed silk fiber equivalent to~40%of the whole cocoons) was obtained as a rawmaterial for the manufacture of daily textile such as silk quilt.The strong alkaline eluent that was circulated several times during the silk flossprocessing and the SAEW refining solution above were firstly separated byultrafiltration into a filtrate and retentate. The filtrate was separated by nanofiltrationinto a purified H2O filtrate that can be recycled as the alkaline eluent and a retentatecontaining oligopeptides and free amino acids with low molecular mass (NR) wasobtained. The ultrafiltration membrane retentate was a sericin polypeptide (UR) with arange of high molecular mass values, and it was hydrolyzed by papain under threedifferent conditions into three groups of sericin peptides with high, middle or lowmolecular mass. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) and gel permeation high-performance liquid chromatography (GP-HPLC)showed the molecular mass of these peptides was in the range of0.2~60kDa,0.2~30kDa and0.2~15kDa. These sericin peptides can be widely used for the polymermaterials surface modification agent, cell culture medium, cosmetic and healthy food,etc.The NR above was continue concentrated to about20%using the rotaryevaporation, the NR finally obtained was used for the synthesis of a lauroylsericin-based surfactant (LSBS) with a yield of~75%. There was no significantdifference in amino acid compositions between NR and LSBS. The critical micelleconcentration (CMC) and the lowest surface tension (γCMC)of LSBS were much lowerthan that of NR, and LSBS had high foaming power. The emulsifying power of NR andLSBS in an oil/water (O/W) phase with the ethyl acetate as the oil phase was better thanthat with the benzene. Generally, the LSBS displayed a good property of surface.Another main byproducts silkworm pupae was obtained from the process of silksheet, approximately accounting for30%of the total cocoon. The defatted pupaeprotein and pupa oil were obtained after the pupa powder was dealt with hexane. Anovel N-fatty acyl amino acid (NFAAA) surfactant was synthesized using pupa oil andpupa protein hydrolysates (PPH) derived from a waste product of the silk industry. Thefatty acids from pupa oil were modified into N-fatty acyl chlorides by thionyl chloride.NFAAA was synthesized using N-fatty acyl chlorides and amino acids from pupaprotein. GC-MS analysis showed fatty acids from pupa oil consist mainly of unsaturatedlinolenic (63.59%) and linoleic acids (4.12%) and saturated palmitic (25.33%) andstearic acids (6.26%). NFAAA had a low critical micelle concentration, great efficiencyin lowering surface tension, and strong adsorption at an air/water interface. Besides,NFAAA had a high foaming power as well as an emulsifying power. The emulsifyingpower of PPH and NFAAA in an oil/water emulsion was better with ethyl acetate as theoil phase compared to n-hexane. This amino acid-based surfactant was entirely derivedfrom the silkworm pupae, it was the same as sericin amino acid based surfactantdescribed above which have wide range of applications in the use of daily chemicalsespecially body wash, shampoo and infant detergent. They novel technologies described in this study containing the improvement of silksheet processing, sericin recycling and controlled enzymatic hydrolysis, synthesis ofamino acid-based anionic surfactants from the byproducts sericin and silkworm pupae.It can provide a comprehensive integrated technology for the sustainable developmentof sericulture, especially for the silk sheet processing enterprise. It not only can reducethe serious environmental pollution resulting from the strongly alkaline waste thatcontains the sericin released from the silk sheet processing, but also can facilitateefficient recovery and use of large quantities of sericin as well as the recycling of waterby membrane filtration. In addition, a daily chemical product amino acid type anionicsurfactant with broad application prospects was developed by use of the recycled sericinand silkworm pupae. This comprehensive integrated technology can promote thesustainable development of sericulture, and bring additional profits for the silk factory.