Study On Technical Characteristics Of In-mold Self-reinforced Molding Of Single Polymer Composites

Single polymer composite is a kind of composite, the matrix and reinforcement made up of same or cognate polymer material, and the significant characteristics of SPC were high specific strength, no interfacial discrepancy, and easy recovery. Manufacturing of SPC by hot compression is the conventional way, but this method has the defects of complicated process, low efficiency and limited material selection, restricting the application of SPC. This paper introduced a new method of manufacturing SPC by co-injection, namely, the matrix and reinforcement were molded by injection respectively. Compared with hot compression, co-injection has the strength of simple process, short molding cycle, etc. Matrix, reinforcement and interface of SPC, especially reinforcement and interface performance, had great effects on the whole mechanical properties of SPC. Based on the nature of polymer material, different molding technology parameters corresponded to different part performance. In this paper, the influence of molding process parameters on the molding of SPC reinforcement was studied by means of physical visualization and sensor measurement.Mechanical performance specimens of PP SPC under different molding condition were made, the unreinforced one as control group. The result of the test indicated that when plasticizing temperature was 230℃ and injection rate 6.11cm/s, tensile strength of SPC specimen reached peak, exceeding the comparison by 23.79%.The filling speed curves of PP melt flow front were obtained by visualization technology. Results showed that filling speed of melt was faster on existence of matrix, so character of self-reinforcement of polymer could function more fully by co-injection technology; when dimensions of reinforcement were 2mm,1.5mm, and lmm, melt could successfully fill cavity fully, but short shooting happened for the 0.5mm. What’s more, under same molding condition, PP melt run faster in smaller grooves than the lager in early stage, but opposite in the middle and later period.Sensors were utilized to measure the cavity pressure and melt temperature in three different locations, namely, near gate, middle and end of the cavity, during the 2mm reinforcement filling grooves within the matrix. Actual filling speed was the dominant factor influencing cavity pressure. During molding process, heat loss by conducting between melt and contact surface, and viscous dissipation were the main affecting factors of melt temperature for certain molding parameter.MoldFlow was used to simulate the injection process in the experiments, including filling process of SPC of different reinforcement dimension and melt into metal grooves, and analysis was realized through aspects of melt front temperature and re melting zone. The higher the plasticizing temperature and larger the injection rate, the higher was the melt front temperature and the more extensive was re melting zone. Contacting with result of mechanical property test, it is the performance of interface, except reinforcement property, that played another dominant role in property of SPC. Other simulation results were corresponding to the experiment generally.