Polypropylene/ethylene-propylene rubber (PP/EPR) blends for the automotive industry: Basic correlations between EPR-design and shrinkage

The influence of the phase morphology on the shrinkage of injection molded plates from reactor based PP/EPR blends was investigated using a model series. The morphology of the dispersed phase - in terms of size and shape of the rubber particles as determined from scanning electron microscopy (SEM) - was found to correlate fairly well with the shrinkage determined in the flow and transverse direction of injection molded plates. In this respect it turned out to be elementary to consider the anisotropy of the particles rather than their average size alone. Additionally, the effect of the EPR design on the coefficient of linear thermal expansion (CLTE) was evaluated and brought into a relationship with the blend morphology.