Study on the β to α transformation of PP/POE blends with β-phase nucleating agent during the tensile deformation process

As a part of serial work about the toughening effect of elastomer and nucleating agent on polypropylene (PP), this work is focused on the microstructure changes of PP matrix in PP/elastomer blends with beta-phase nucleating agent (beta-NA) during the uniaxial tensile deformation process. The microstructure changes have been investigated through differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) measurements. The results show that there is a transformation of beta-PP to alpha-PP, which is dependent on the local strain of the tensile-deformed specimen during the deformation process. The bigger the local strain, the high the degree of the beta -> alpha transformation is. At the later stage, beta-PP is completely changed into alpha-PP. The presence of elastomer, especially at high load, prevents such transformation, possibly leading to more beta-PP participating in the later deformation process of the fracture, which most likely results in the great improvement of fracture toughness of PP/elastomer/beta-NA. Further results show that the beta -> alpha transformation occurs mainly in the necking region of the specimen during the deformation process. (C) 2009 Elsevier B.V. All rights reserved.