Impact Modification of Polypropylene with Ethylene-α-olefin Copolymers: Influence of Density and Comonomer Type on Structure and Properties

摘要

One of the most important applications of ethylene-co-α-olefin (EOC) plastomers based on single-site catalysts (SSC) is the impact modification of polypropylene (PP) homo- and copolymers. Different α-olefins like butene-1 (C4) and octene-1 (C8) are known to give different correlations both between comonomer content and density resp. crystallinity and between EOC amount and PP composite performance. In the present study, two series of SSC-based plastomers with C4 and C8 were tested in combination with PP homopolymers to quantitatively assess the resulting particle size distributions and impact performance. Modulated AFM tests were used for determining particle size as well as modulus ratio between the phases wherever possible, while falling weight impact tests were applied in the mechanical characterization backed up by dynamic-mechanical tests (DMA). At constant viscosity ratio, a clear trend with respect to density difference between the matrix (PP) and the dispersed elastomeric phase (EOC) was found. Surprisingly the type of comonomer - C4 vs. C8 - slightly influences the phase structure even at constant density of the modifier. Calculations of the interfacial tension were done based on rheological measurements using the Gramespacher-Meissner approach.