Injection molding-induced morphology of thermoplastic polymer blends

Various morphologies induced by injection molding are reviewed here. The structural hierarchy in the direction perpendicular to flow direction always appears in the injection-molded blends. The hierarchy involves three aspects: phase behavior hierarchy for the dispersed phase, crystalline or orientated structural hierarchy for the matrix, as well as hierarchy structure of co-continuous phase morphology. There are usually three layers in the injection-molded bars, i.e., the skin layer and the core region as well as the shear zone between them. The morphology of the dispersed phase is usually different between the skin zone (usually including shear zone) and the core region: deformed particles may exist in the skin layer, whereas spherical droplets in the core region. Moreover, the size of crystals usually increases with the increase of the distance to the surface due to the increase of crystallization time, and the orientation is often severe near the surface due to the high shear stress. Defects of the injection-molded parts, such as weldline and flow marks, are also reviewed. The dispersed phase morphology in the weldline region is significantly different from the region out of the weldline and the morphology of the flow marks is also different from the out-of-flow marks.