Study On The Effect Of Molding Parameters On Single Polymer Composites That Prepared By Co-injection Molding Method

With the development of polymer materials and related technology, polymer materials were widely used in our daily life and industrial production. Many kinds of polymers and polymer composites were emerging. Single polymer composites were proposed in 1980s. The matrix and reinforcement of single polymer composites were the same polymer or the homologous series. Therefore this kind of composites had no compatibility problem between matrix and reinforcement, and it could be recycled directly. Because of the continuous efforts of researchers all over the world, single polymer composites have been developing rapidly. But at the same time they were facing a variety of challenges, such as polymer fibers lost mechanical properties during forming process, materials'properties could not be controlled and so on. This paper proposed a new single polymer composites forming method called "Co-injection moulding method" in response to the problems in traditional single polymer composites forming methods. Using a new set of mold, we produced single polymer composites with different reinforcement structures successfully.In this paper polypropylene (PP) was used to produce single polymer composites. Through the comparison of tensile strength we found that single polymer composites with different reinforcement had different tensile strength and they were all higher than common polymers. The tensile strength of single polymer composites which had five reinforcements was the highest Otherwise, the comparison of single polymer composites and common polymers showed that single polymer composites might bend and had shrinkage marks. They also had different fracture states during tensile test. The influence of injection rate, melt temperature and mold temperature on single polymer composites'mechanical properties were studied. Results showed that, in the case of other molding parameters unchanged, when injection rate and melt temperature, the tensile strength of single polymer composites decreased. The effect of mold temperature had not significant laws. But higher tensile strength usually occurred in the lower mold temperature. These three factors affected the tensile strength to different degree, melt temperature had the greatest impact and injection rate had a minimal effect.Materials mechanical properties and micro-structure of materials had close relationship. This paper used scanning electron microscopy (SEM), X-ray diffraction and polarizing microscope to analyze single polymer composites. The results showed that, due to low molding temperature, there was stripping phenomenon between reinforcement and matrix of single polymer composites which had the best mechanical properties. Conversely the lowest mechanical properties specimens had better interface because of high molding temperature. Polarizing analysis showed that molding parameters had significant effect on the crystallization of the reinforcement. Increasing of injection rate and melt temperature would make the skin layer of the reinforcement to be thin. And the effect of mold temperature had not significant laws. X-ray diffraction results showed that single polymer composites had strongest diffraction peaks of ?-crystal, unlike common polymers which was ?-crystal. The higher tensile strength single polymer composites was, the higher ?-crystal crystallinity it had. And its crystal preferred orientation was also stronger. Different single polymer composites had different diffraction peaks value and they had regular changes. The single polymer composites which had five reinforcements had the maximum diffraction peaks value and its crystallinity was also the highest.