pps proceeding - Abstract Preview

Investigation on Crystallization Kinetics and Injection-Molding Induced Crystallization of Isotactic Polypropylene

Spoerer Yvonne ^(1)*, Boldt Regine ⁽¹⁾, Androsch René ⁽²⁾, Kuehnert Ines ⁽³⁾

⁽¹⁾ Leibniz-Institut fuer Polymerforschung Dresden e.V. - Dresden - Germany, ⁽²⁾ Martin Luther University Halle-Wittenberg - Halle Saale - Germany, ⁽³⁾ Leibniz-Intitut fuer Polymerforschung Dresden e.V. - Dresden - Germany

Isotactic polypropylene (iPP) is a semi-crystalline polymorphic thermoplastic. This means that iPP can crystallize into α-, β-, or γ-modification, as well as form a mesophase depending on the crystallization conditions. If the material is processed by injection molding, the macromolecules are exposed to thermal and mechanical forces, which vary according to the processing conditions (temperature, pressure, melt-flow rate, mold geometry). As a result of these forces, the macromolecules in the melt may align/orient, leading to shear-induced formation of nuclei, and influencing the crystallization process including the final supermolecular structure of the molded part. This study focuses on the analysis of crystallization kinetics of iPP designed for injection molding and the characterization of the process-induced supermolecular semi-crystalline structure. Using differential scanning calorimetry (DSC) and fast scanning chip calorimetry (FSC), the crystallization behavior was analyzed as a function of temperature and cooling rate. The results allowed drawing conclusions about temperature-ranges and cooling rates that are needed to obtain the mesophase and/or α-crystals. According to the thermal investigation, the material was injection molded with varying process temperatures (melt and mold) and investigated in terms of the semi-crystalline structure and crystallinity by using polarized-light optical microscopy (POM) and DSC, respectively. The results show the influence of the temperature difference between the melt and mold on the crystalline fraction and spherulite-size distribution from skin to core in the injection-molded parts. This research forms part of the DPI programm, #816t18. The results contribute to the description of the relationship between the crystallization kinetics of the material and the process parameters influencing the injection-molding induced morphology. This is required to realize process control in injection molding in order to produce pre-defined morphologies and to improve the material behavior.