Papain Degumming Process And Physical And Chemical Properties Of Silk Fibroin Materials After Degumming

Silk degumming method and quantitative detection method of containing sericin ratio are urgent problems in the field of medical silk fibroin purification and silk fabric refining.The goal of improving the current degumming process is to remove all the sericin from the periphery of the silk,and to avoid the hydrolysis damage of the silk fibroin during the degumming process.Papain has mild conditions and strong specificity to sericin,which is a natural degumming agent with potential for development and application.In this paper,we first studied the effect of papain solution concentration on the degumming effect of silk.Secondly,based on the most significant difference between silk fibroin and sericin amino acid composition,the relationship between containing sericin ratio of silk and ratio of aspartic acid/alanine was established,which provided a new quantitative method for the containing sericin ratio of the unknown silk.And the containing sericin ratio of silk after degumming with papain was measured.Then,in order to obtaned a new method to reduce the concentration of papain,the silk was degummed by the combination of the lower concentration of papain solution and the ultrasonic treatment.Finally,the silk fibroin/sericin blend membrane was prepared by casting method,and the effect of blending ratio on the physical and chemical properties of the membrane was discussed.Firstly,the silk was degummed with papain at a concentration of 0.01?6 g/L,so as to investigate the degumming effect on silk.The results of gravimetric method,dyeing method and SEM showed that the degumming rate of papain at a concentration of 3 g/L was 22.73±0.08%.The surface of the fiber after degumming was smooth,and it showed yellow after staining with picric acid carmine,which indicated that the sericin was basically exhausted.Compared with 0.5 g/L Na2CO3 degumming,the mechanical properties of silk were improved after degumming with 3 g/L papain,and the molecular weight of silk fibroin obtained was increased significantly.Secondly,the sericin/silk fibroin solids were obtained by freeze-drying method,which sericin accounted for total quality of fibroin and sericin were 0/100?30/100.The relationship between containing sericin ratio and Asp/Ala was investigated by amino acid analysis.The results showed that the linear relationship between containing sericin ratio y(%)and Asp/Ala x(%)was y=2.6913x-14.2885,that calculating the containing sericin ratio of 3 g/L papain was 0.01%,and it showed that the sericin had been exhausted.However,the containing sericin ratio of 0.5 g/L Na2CO3 was-0.37%,which showed that excessive degumming and part of silk fibroin had been hydrolyzed.Then,the raw silk was pretreated with deionized water at 80? for 2 h,and the degumming effect of ultrasonic treatment with a power of 200?500 W and a frequency of 28?100 kHz combined with 1 g/L papain was investigated.The results of containing sericin ratio and SEM showed that firstly carried out with 1 g/L papain,and then further processed by 500 W and 45 kHz ultrasonic,which containing sericin ratio was only 0.57%.and sericin had been nearly exhausted.The mechanical properties and thermal stability could be improved,and the obtained silk fibroin had a higher molecular weight.Thus,a new process for degumming silk with a lower concentration of papain was obtained.Finally,The silk fibroin/sericin blend film with mass ratio of 100/0?0/100 was prepared by casting method,and the effect of blending ratio on the physical and chemical properties was investigated.The results of SEM and AFM showed that with the increase of the proportion of sericin in the silk fibroin/sericin blend film,the surface aggregation phenomenon and the surface roughness of blend membrane were increased,but there was no obvious phase separation.Infrared spectroscopy,X-ray diffraction and amino acid analysis showed that the cross-linking reaction of PEG-DE occurred not only between silk fibroin-silk fibroin,silk fibroin-sericin,but also in silk fibroin-sericin between macromolecules.When the proportion of sericin in the silk fibroin/sericin blend membrane increased,the crystallinity of the blend membrane was decreased,moisture content and dissolution rate of the silk fibroin/sericin blend membrane was increased,and the mechanical properties were decreased accordingly.