Crystal Morphology of Water-Assisted Injection Molded High-Density Polyethylene with Two Different Molecular Weights

The crystal morphology of water-assisted injection molded (WAIM) parts of high-density polyethylene (HDPE) with two different molecular weights was investigated. The results showed that for the WAIM parts of HDPE with higher molecular weight, oriented lamellar structures formed in the outer layer, whereas spherulites formed in the core and inner layers, at positions both near the water inlet and near the end of the water channel. However, for the WAIM parts of HDPE with lower molecular weight, spherulites formed in all three layers at a position near the water inlet, whereas oriented lamellar structures formed in the outer layer and banded spherulites were dominant in both core and inner layers at a position near the end of the water channel. The crystal morphology development was interpreted with the aid of stress and temperature fields within the mold cavity under melt filling and high-pressure water penetration during the WAIM.