The Improvement And Prediction Of The Mechanical Properties Of Natural Fiber Reinforced Thermoplastic Composites

Owing to the advantages of low cost, low power consumption, environment-friendly and sustainable development, natural fiber reinforced thermoplastic composites are getting great attention and applications. However, there are many problems that need to be solved. In this thesis, some issues are studied in the improvement of the mechanical properties of natural fiber composites. Sisal fiber and polypropylene are as reinforcement and matrix, respectively.In order to improve the mechanical properties of composites, three methods were used. The first method was fiber inherent treatment. This treatment is like the biomineralization of wood materials. The mechanical properties and cross-sections of single fibers and composites with and without this treatment were evaluated. The mechanism of combined modification by the biomineralization and KH550 silane was analyzed. The second method was interfacial reaction and compatibilization between fiber and matrix. The interfacial reaction and adhesion were enhanced by adding compatibilizers and activating fiber surface. The third method was hybrid by inorganic fillers and fibers. The effects of this hybrid on the mechanical properties of composites were investigated, and the modulus of the composites were improved greatly.The fiber distribution of the composite was quantified. The effects of compounding technologies and fiber treatments on fiber distribution were analyzed. The influences of fiber distribution on the mechanical properties of composites were studied.In order to improve the interfacial adhesion, understand interface formation and prepare high performance composites, the impregnation of polypropylene into fiber beds were investigated. The spontaneous wettability and spreading of matrix on fibers were estimated. The effects of capillary force on the composite preparation were analyzed.The impact properties of composites were studied in detail. The influences of fiber contens, matrix and compatibilizer types on the impact properties were analyzed. The stochastic fiber properties were researched, and the tensile strength of fibers at critical fiber length were calculated by using modified Weibull model. The prediction for impact properties of composites were performed.The GMCL model for the prediction of mechanical preoperties was put forward based on Generalized Method of Cells and Laminate Analogy Approach. The effects of fiber volume fraction, fiber shape, fiber distribution, fiber size and interface between fiber and matrix on the mechanical preoperties were predicted by the GMCL model.Some electrical cover products were made by natural fiber composites. The products defects were analyzed, and natural fiber composites for the electrical cover applications were preliminary discussed.In this thesis, some new researches were performed such as fiber inherent treatment, the quantitative description of fiber distribution, the improvement of impact strength and the prediction of mechanical properties of composites. And the better results were obtained.