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

摘要： 针对聚己内酯(PCL)力学强度不足的问题，以单向蚕丝片为增强体，PCL为树脂基体，通过热压成型工艺制备了单向蚕丝/PCL复合材料。为了获得界面结合良好的单向蚕丝/PCL复合材料，采用Na2CO3溶液对单向蚕丝片进行脱胶处理。利用扫描电镜、接触角测定仪、万能强力仪、摆锤冲击试验机、热重分析仪等研究了不同质量分数的Na2CO3溶液脱胶处理对单向蚕丝片表面性质及蚕丝/PCL复合材料力学性能和热稳定性能的影响。结果表明：经过脱胶处理后，单向蚕丝片浸润性改善；当在1.5%Na2CO3溶液中脱胶1 h后，蚕丝表面丝胶基本除尽，树脂基体对单向蚕丝片浸润效果良好，复合材料中单向蚕丝片与PCL基体结合紧密，单向蚕丝/PCL复合材料的力学性能最好；与未脱胶单向蚕丝/PCL复合材料相比，弯曲强度和冲击强度提高了87.06%和56.25%；单向蚕丝片脱胶处理后，单向蚕丝/PCL复合材料的热稳定性能变好。脱胶处理后的单向蚕丝片作为增强体应用于可降解复合材料中，获得的单向蚕丝/PCL复合材料界面结合良好、力学性能优良，表明其在可降解天然纤维增强复合材料领域中应用潜力巨大。

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