Rheological Behavior of Impact Polypropylene Copolymer and Its Fractions

Abstract

The dynamic rheological behavior of the melts for an impact propylene copolymer(IPC) and its three fractions were examined.The results show that the dynamic storage modulus(G′) of IPC exhibits "pseudo solid-like" behavior at low frequency(ω),i.e.a "second plateau" appears in the lgG′ vs.lgω plotting.This phenomenon indicates that the IPC melt is endowed with a characteristic of heterogeneous phase.The differences in G′ and complex viscosity(η*) among the fractions of IPC appear dramatic,which are probably induced by the differences of the molecular weight and the length of the molecular chains among the fractions.The dynamic rheological behavior of the EPR and HPP fractions well accord with the linear viscoelasticity,implying that these fractions are homogeneous system.Moreover,the dynamic rheological behavior of the EbP exhibits "pseudo solid-like" behavior at low ω,meaning that this fraction is a heterogeneous system.On the other hand,the "second plateau" can be observed in low ω region for the HPP/EPR blends when the proportion of the EPR is the same as the proportion of EPR in IPC,suggesting that the "second plateau" in IPC results from the phase-separation between HPP and EPR,and the existence of EbP does not play a key role in the generation of "second plateau" in IPC.