Morphology-Property Behavior of Semi Crystalline Polymers in Injection Molded Parts

During injection molding different types of interfaces (weld lines) are formed. The skin-core morphology in particular is affected by the cooling conditions (temperature difference between melt and mold) during the process. Inside the injection molded part the development of the structure depends on the melt flow conditions and the mold design, e.g. at the weld lines. Possible reasons for the development of weld lines are the division of the melt flow by flow obstacles or the use of multiple gates to create complex and/or large parts. this characteristic leads to optical irregularities and/ or mechanical weaknesses due to the structural orientation, which depends on thermodynamic and morphological behavior of the polymer chains. For a better understanding of the specific orientation of the molecular chains it is necessary to know how the structural development is affected by the processing conditions. Here an overview about the influence of the injection molding process on the crystalline morphology and the relation to mechanical properties for different semi-crystalline polymers is given. The crystalline morphology of the samples is visualized by using polarized light microscopy (POM) and the mechanical behavior is measured using a tensile test.