Validation of a model to predict birefringence in injection molding

The current goal in the simulation of injection molding is the description of material morphology. The path to reach this goal passes through the prediction of molecular orientation and strain, namely the molecular conformation. To obtain this information, the viscoelastic nature of the polymer must be taken into account. The aim of this paper is to check if a simple, recently proposed, non-linear dumbbell model is sufficiently accurate to quantitatively describe birefringence distribution in injection molded PS samples. To this goal, a series of rheological measurements were performed in a parallel plate rheometer, measuring in the meantime the birefringence. By choosing an appropriate stress-optical coefficient, the model could describe the whole set of data. The results obtained allowed to reinterpret some results of molecular orientation in injection molding and to reach a quantitative description of data of birefringence distribution in molded PS samples.