The microstructure of a molded product considerably influences its macroscopic properties. In this study, the influence of molding process on microstructure, tensile property, and surface quality was explored on the glass fiber-reinforced polypropylene (GFRPP) parts molded by rapid heat cycle molding (RHCM) and conversion injection molding (CIM). Tensile strength and surface gloss were chosen to measure macroscopic properties of the molded parts. The microstructure including multilayer, fiber orientation, crystallinity, and fiber-matrix bonding strength were analyzed by simulations, scanning electron microscopy, wide-angle X-ray diffraction, and dynamic mechanical analysis. The relationship between the macroscopic properties and microstructure of the RHCM samples was also discussed. The results indicate that as the mold cavity surface temperature increases, the tensile strength increases firstly and decreases thereafter. The tensile strength of RHCM parts reached the maximum at the mold heating temperature of 60°C. It is also observed that the surface gloss of the sample increases as the mold cavity surface temperature rises, and the increase of surface gloss decreases distinctly with the mold heating temperature higher than 90°C.
Performance of the rapid heat cycle-molded products is highly correlated to its multilayer structure and crystal form in the multilayers. In this study, isotactic polypropylene was introduced in molding experiments, multi-sites sampling was carried out, and β-crystal contents together with multilayer structure were characterized by scanning electron microscopy and X-ray diffraction. It is shown that the distribution of β-crystal is significantly relevant to the multilayer structure. Meanwhile, a higher mold-heating temperature would benefit the formation of β-crystal, the content of which is mainly dependent on mold temperature and filling distance.
Abstract.Fiber-reinforced plastics exhibit many merits and injection molding is one of the most common method for the production of plastics. Therefore, injection-molded fiber-reinforced plastic products have been widely used and their properties and structure were studied in the present work. The influences of fiber type, fiber content, and processing on the internal morphological structure of the injection-molded composite materials were investigated. Moreover, the change of performance of plastic products was analyzed.
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