Isotropy of mechanical properties and environmental stress crack sensitivity in injection- and injection-compression molding of polystyrene with different mold temperature

Abstract

In addition to conventional injection-compression molding and injection molding with dynamic process temperature control, a synergistic combination of both processes has recently been applied in dynamic temperature-controlled injection-compression molding. The two-dimensional holding pressure effect in combination with the long maintenance of the flowability of the melt due to high mold temperature enables particularly large flow path to wall thickness ratios. In the most cases, only the optimized molding of microstructures and aspect ratios is considered without including the changed internal structure of such manufactured components. In the course of this investigation, the influence of different process strategies under variation of the mold temperature on production-related anisotropies in the mechanical properties and stress crack sensitivity of thin-walled polystyrene components was examined. The determined mechanical properties are significantly below the values given in the data sheet of the material in the adapted process variant of injection-compression molding with high mold temperature. However, the results also show a clear homogenization of the direction- and flow path-dependent mechanical properties. In contrast, components produced in this way tend to show increased environmental stress crack sensitivity. This could be attributed to significantly reduced orientations as a result of the favorably proceeding orientation relaxation.