Mechanical properties and morphology of polypropylene/polystyrene blends

In this article the relation between the morphology and macroscopic mechanical properties, i.e., stiffness and strength, of blends of polypropylene (PP) and polystyrene (PS) within the framework of micromechanics of composite materials was studied. Test results on tensile properties of immiscible PP/PS blends showed that the micromechanical models were valid for the prediction of elastic moduli. The Mori-Tanaka model would be a more effective method for designing materials in comparison with the Halpin-Tsai model and the modified mixture model because there is no restriction on the experimental parameters. The ultimate strengths were predicted in terms of pure component strength and composition. On the basis of the assumption that the ultimate strength will be controlled by the dispersed phase when the blend has more than the minimum fraction, the minimum fraction of dispersed phase calculated was found close to the phase inversion region determined by observing the blend morphologies. It is confirmed that the blends have a stationary mechanical property at the phase inversion region. Because the poor interface was not taken into account and an assumption was made for the failure of the entire dispersed phase, the model gave an overestimate for strength.