关键词: 蚕丝, 聚己内酯, 复合材料, 蚕丝脱胶, 热压, 力学性能, 热稳定性能

Abstract:  In recent years, with the popularity of the concept of green environmental protection and low-carbon development, biodegradable natural fiber reinforced composites have become a hot research point in the field of polymer material research. In this paper, one-way silk sheet was used as reinforcement, polycaprolactone was used as resin matrix, and one-way silk sheet was degummed with different mass fractions of Na2CO3 solution. The effects of different mass fractions of Na2CO3 solution on the surface morphology and wettability of one-way silk sheet were investigated. One-way silk/PCL composites were prepared by hot pressing molding, and the effects of degumming treatment of one-way silk sheet on the interfacial bonding, mechanical properties and thermal stability of composites were studied.
 In this study, 0.0%, 0.5%, 1.0%, 1.5% and 2.0% Na2CO3 solutions were used to degum the one-way silk sheet after drying. The degumming rate was calculated and the contact angle was tested. The surface micro-topography of the one-way silk sheet before and after degumming was photographed by SEM. The degummed one-way silk sheet was immersed in PCL solution, and then the one-way silk/PCL composites were taken out and tiled in a ventilated environment. After the volatilization of dichloromethane, the one-way silk/PCL composites were prepared by tiled hot pressing. The bending resistance and impact resistance of one-way silk/PCL composites were tested and characterized by SEM. The effect of one-way silk sheet degumming on the thermal stability of one-way silk/PCL composites was studied by thermogravimetric analysis.
The results showed that with the increase of Na2CO3 mass fraction, the sericin, grease and impurities on the surface of silk were gradually removed, the one-way silk sheet performed better in wettability and became looser, the infiltration effect of resin matrix on one-way silk sheet became better, the combination of silk and PCL matrix was closer, and the mechanical properties of one-way silk/PCL composites were significantly improved. When the mass fraction of Na2CO3 was 1.5%, the sericin on the surface of silk fiber was basically removed, and the mechanical properties of one-way silk/PCL composites reached the highest level, which were 126.19 MPa and 133.33 kJ/m2, respectively. Compared with the un-degummed silk reinforced composite material, the bending strength increased by 87.06%, and the impact strength increased by 56.25%. The results of thermogravimetric analysis showed that the thermal stability of one-way silk/PCL composites was improved by degumming. It can be seen that the most suitable amount of Na2CO3 for one-way silk sheet degumming treatment is 1.5%. One-way silk sheet degumming treatment improves the infiltration effect of PCL resin matrix and silk fiber, improves the mechanical properties and thermal stability of one-way silk/PCL composites. The research results can provide reference for expanding the application of one-way silk sheet in the field of natural fiber reinforced composites.

Key words: silk, PCL, composite materials, silk degumming, hot pressing, mechanical properties, thermal stability