Cellular structure and mechanical strength of straw fiber/polypropylene plastics under chemical foam molding

Plant fiber-reinforced polypropylene composites are low-cost, good-performance and resource-saving, so has wide application prospect in automotive components. While the density of composites increases with the increase in the plant fiber content, the chemical foaming injection process was used to prepare straw fiber/PP foamed composites with exothermic foaming agent azodicarbonamide, in order to reduce the density of composite products and meet the requirements for lightweight automotive trim parts. The effects of temperature and fiber content on the mechanical properties and microstructures of the composites were investigated. Research results show that the microporous straw fiber/PP composites have close bond with the core layer fibers, the matrix, and the cells. The cells evenly distributed around the fibers to form a ‘sea island’ phase structure of the fiber microporous matrix, and the toughness of microporous sample is better than solid composites. Within a certain range, the cell density and the impact resistance of the microporous composites increases first and then decreases as the molding temperature increases, and maximize at 185 °C. Straw fiber plays a role of nucleation and toughening in the microporous straw fiber/PP composite system. And as its content increases, the cell density increases, similarly the toughness of the composites increases.