Oriented Crystallization and Mechanical Properties of Polypropylene Nucleated on Fibrillated Polytetrafluorethylene Scaffolds

It is known that friction deposited polytetrafluoroethylene (PTFE) layers are able to nucleate crystallization of thin films of isotactic polypropylene (iPP). In order to investigate the influence of PTFE on the crystallization behavior and morphology of iPP in bulk, PTFE-particles of two different sizes in various concentrations were melt-blended with iPP and subsequently processed by injection molding. For one size of particles, high resolution scanning electron microscopy (HR-SEM) showed the presence of a PTFE scaffold consisting of highly fibrillated PTFE particles. With X-ray diffraction (WAXD) pole-figures, it was evidenced that, after melting and recrystallization of the iPP matrix, a strongly oriented crystallization of iPP on this PTFE scaffold takes place (quiescent crystallization conditions). With WAXD it was also shown that under processing conditions, PTFE acts as a nucleating agent for iPP and that PTFE strongly enhances the formation of processing induced morphologies. Impact and tensile performance of the mixtures were measured. Both the strain energy release rate (GI) and the E-modulus were found to increase upon introducing PTFE in iPP. POLYM. ENG. SCI., 45:458-468, 2005.