Abstract:

Plant protein derived from waste seed meal after oil extraction has been emerged as an important natural and renewable source for the preparation and production of environmentally friendly green materials. Compared to synthetic polymers, protein-based polymer materials, however, have lower mechanical properties and inferior thermal stability. To this end, natural plant fibers have been often incorporated into the protein matrix to reinforce them and to improve properties of the resulting composites. In this work, we used oriented natural sisal fiber (SF) as a reinforcement, and dialdehyde starch (DAS) as a green cross-linking agent to prepare cottonseed protein (CP)/SF green composites with desired mechanical properties and tight interfaces between the matrix and reinforcement. Specifically, after successive treatments including urea denaturation, glycerol plasticization, DAS cross-linking, cottonseed protein was mixed and combined with long and oriented SF, and then hot-pressed into CP/SF green composites. Tensile tests showed that with the incorporation of 5%(mass) SF, the fracture stress of CP matrix increased from 0.35 MPa to 1.28 MPa. The effects of DAS content on mechanical properties and thermal stability of the composites were investigated. Tensile tests, TGA and DSC showed that the composite with 20%(mass) DAS crosslinker exhibited the highest tensile strength (fracture stress 7.5 MPa), modulus (Young's modulus 93 MPa), thermal stability (maximum decomposing temperature 328℃) and glass transition temperature (102℃). Experimental evidences of the chemical structure, microscopic morphology and property analysis suggest that the improvements in the composite properties is mainly due to three factors: the formation of tight interfaces between CP matrix and SF reinforcement, the impregnating pretreatment on unidirectional arranged fiber, and the strong hydrogen bond forces between CP and SF biomacromolecules. The formation of imine bond detected by FTIR spectra at peak position of 1652 cm^-1 indicates that successful cross-linking reaction is taken place between DAS and CP/SF. From both surface and cross-section view of sample SEM images, tight CP/SF interfaces are clearly noticed where both components are closely attached with each other, creating strong bridges linking the protein and oriented fiber.

Key words: composites, interface, mechanical properties, cottonseed protein, natural fiber, cross-linking

摘要：

为了提高植物蛋白基绿色高分子材料的力学性能和热稳定性能，以棉籽蛋白（CP）为原料，在尿素变性、甘油增塑、双醛淀粉（DAS）交联的基础上，将其与取向排列的天然剑麻长纤维（SF）复合，经热压硫化加工制备得到具有优异性能的棉籽蛋白/剑麻纤维全绿色复合材料。微观结构形貌和性能分析测试表明，复合材料获得改善性能主要归功于：CP基体与SF增强相间形成的紧密界面结合、对剑麻长纤维的预浸渍处理、CP与SF生物大分子间的强氢键作用。考察了不同DAS含量对复合材料力学性能和热稳定性能的影响。拉伸、热重和差示量热分析表明，经20%（质量） DAS交联的复合材料具有最优的拉伸强度（断裂应力7.5 MPa）、模量（杨氏模量93 MPa）、热稳定性（最大分解温度328℃）和玻璃化转变温度（102℃）。

关键词: 复合材料, 界面, 力学性能, 棉籽蛋白, 天然纤维, 交联