Morphology and mechanical property of high-density polyethylene parts prepared by gas-assisted injection molding

The crystal morphology, melting behavior, and mechanical properties of high-density polyethylene (HDPE) samples obtained via gas-assisted injection molding (GAIM) under different gas pressures were investigated. Moreover, the non-isothermal crystallization kinetics of HDPE under different cooling rates was also studied. The obtained samples were characterized via differential scanning calorimetry, two-dimensional wide-angle X-ray scattering (2D-WAXS), tensile testing, dynamic mechanical analysis (DMA) and scanning electron microscopy techniques. It was found that the properties were intimately related to each other. Macroscopically, the flow-induced morphology of the various HDPE samples was characterized with a hierarchical crystalline structure, possessing oriented lamellar structure, shish-kebab structure, and common spherulites in the skin, sub-skin, and gas channel region, respectively. The 2D-WAXS results demonstrated that the degree of orientation of the high gas pressure sample was larger than that of the low pressure sample at the corresponding layer. The tensile testing results of GAIM parts showed that the mechanical properties of the GAIM parts were improved with an increase of the gas pressure. Furthermore, the DMA was utilized to obtain the dynamic mechanical properties of the GAIM samples, and the results indicated that significant improvement of the orientation was observed with an increase of the gas pressure.