Investigation On Influence Of Processing Flow Field On Properties Of PP/Sisal Fiber Composites

The natural thermoplastics/fiber composites are a kind of environment-friendly materials. The plant fiber reinforced thermoplastic composite has some advantages such as light-weight, continual development and so on, and has been used in car and architecture industry.This paper chose sisal fiber and PP. The PP/sisal extruding composites were formed by different screws structure, in which flow field (including distributive mixing, dispersive mixing, chaotic mixing and strong shear flow field) are different. Then, composites were formed by the injection molding and injection compression molding. Scanning electron microscopy and optical microscope were used to analyze the fibers'dispersion and orientation. Mechanical properties of extruding, injection molding and injection compression molding composites were tested. Infrared spectrum and thermo-gravimetric analysis of PP, sisal fiber and composites were measured.The fibers'dispersion was best in composites molded by strong shear flow field, and fiber also was longest. Fiber was shortest in composites part molded by chaotic and dispersive mixing. According to the fiber orientation, three regions across the thickness of injection molding part could be found, including surface, core and surface layer. Five regions could be found in injection compression molding part, including surface, subsurface, core, subsurface and surface layer.Tensile strength and modulus of the composites molded by chaotic mixing were better than that molded by dispersive mixing and distributive mixing, and the same with the injection and injection compression molding composites. The mechanical properties of composites molded by strong shear flow field were best in extruding composites, and the mechanical properties of injection and injection compression molding composites after extruding by strong shear flow field are also best. Mechanical properties of injection compression molding part were better than that of injection molding part, and the part near the gate was better than the end of the same part.Thermo-gravimetric analysis showed that thermal stability of injection and injection compression molding composites was better than that of extruding composites. Examination of infrared spectrum showed the graft copolymerization between PP-g-MAH and sisal fiber existed in composites molded by different flow fields.Based on the previous studies, the model of tensile strength and tensile modulus were constructed with dispersion coefficient and compacting coefficient. Through Experiment, it proved that the dispersion's coefficient calculated by tensile strength model and the tensile modulus predicted were good agreement. During the prediction of impact, there is a little error, but the trend was agreement.