Simultaneously toughening and reinforcing high-density polyethylene via an industrial volume-pulsatile injection molding machine and Poly(ethylene terephthalate)

Abstract It is difficult for polymeric materials to avoid the conflict between the mechanical properties and flowability in manufacturing large-sized injection-molded products. To solve the issue, this paper develops an industrial volume-pulsatile injection molding (VPIM) machine to introduce a high-amplitude vibration force field into the entire injection molding process. As a one-step morphology control, the vibration force field can drive the dispersed Poly(ethylene terephthalate) (PET) droplets to form the stiff microfibrils to improve the mechanical properties of the high-density polyethylene (HDPE) with high melt flow index (MFI). HDPE matrix is toughened and reinforced simultaneously under the synergistic effect of VPIM and PET. The impact and yield strengths of the HDPE/PET composite sample prepared by VPIM are increased by 696% and 28.5%, respectively, compared with that of the pure HDPE sample prepared by conventional injection molding (CIM). The optimal process frequency is found to be 0.5Hz for the mechanical properties of HDPE/PET composite. The phase and impact-fractured surface morphologies indicate that the dramatic improvement of the mechanical properties should be attributed to the in-situ formation of PET submicron-fibrils and hybrid shish-kebabs in the intermediate region. The morphological analysis results are verified by DSC, DMA, 2D-WAXD, and 2D-SAXD tests. From a multi-physics perspective, the influencing mechanism of the vibration flow field on the morphology is put forward to reveal why the mechanical properties of HDPE/PET composite are the best at 0.5Hz.