Vibration-Induced Self-Reinforcement of Injection Molding Samples of High-Density Polyethylene

A pressure vibration injection machine with vibration frequency of 0–1.5 Hz and vibration pressure of 0–75 MPa was developed to investigate self-reinforcement of high-density polyethylene (HDPE). The effect of vibration frequency and vibration pressure on tensile strength and elongation of HDPE DGDA6098 vibration molding samples, which were obtained at different melt temperatures, was studied, and SEM and WAXD measurements were conducted. Experimental results showed that vibration changed the crystal structure of vibration samples and enhanced their orientation. Instead of spherulites of static samples, crystal structure of vibration samples was lamellae that was orientated along melt flow direction. When vibration frequency was high, lamella size was small and orientation degree was low. When vibration pressure was high, lamella size was large and orientation degree was high. Therefore, vibration samples were self-reinforced with increasing vibration frequency and vibration pressure, where the maximum increment of tensile strength was 41.0 %.