Injection Molding Of Long Glass Fiber Reinforced Polypropylene Assisted By Foaming Process

Fiber-reinforced composites(FRT)have become more and more widely used in automotive,architectural and aerospace applications due to their excellent properties,especially long fiber reinforced thermoplastic composites(LFT),however,the mechanical properties of FRT have a direct relationship with the length of fiber,and fiber breaks very seriously during the injection molding process,resulting in the reinforcing effect of the fiber does not achieve the desired effect.In this paper,the long fiberglass-reinforced polypropylene(LGF/PP)was used as an example to count the length distribution of the fibers in the injection molding machine during conventional injection molding and injection foam molding,analyzing the mechanism of fiber breakage and the protective mechanism of foam on fibers.According to the phenomenon that foaming has a protective effect on fibers during injection foaming and the residual fiber length in products is longer,however,the mechanical properties of its products are not as good as those of conventional injection molding due to the weakening of the cell,this paper proposes a new molding method that improving the mechanical properties of the product by compacting and defoaming.The specific study is as follows:(1)Compared with the length and distribution of each segment of fiber in conventional injection molding,the proportion of the fiber length at 0-1mm in screw head,nozzle,and product in injection foam molding is reduced,and the fiber length in each section above 1mm is reduced increased.Moldflow software was used to simulate and analyze the impact of foaming on the fiber breakage during injection molding.After injection foaming,the residual fiber length in the product was longer than the conventional solid injection.With the increase of the initial concentration of gas,the residual length of the fiber gradually increased in the product.(2)Studying the effect of foam on the fracture of the fiber by controlling the injection process parameters and the foaming system in the injection molding process,the foaming quality is fine when the injection parameters and the foaming system are reasonable,and the fiber is protected well by cell during the filling process.The residual length of the fiber in the product is larger,resulting in good mechanical properties in products.(3)Not only does the method of compacting and defoaming make full use of the protective effect of the foaming matrix on the fibers,but also avoids the weakening of the cells.Comparing with the conventional injection molding,it has increased the length of the fiber by 50.9%,the tensile strength 17.95%,the bending strength by 25.58%,and the impact strength by 26.79%.