EFFECT OF AMORPHOUS PHASE ON THE VOID PROPAGATION AND RELATED FRACTURE IN ISOTACTIC POLYPROPYLENE

摘要

@@Tensile deformation of isotactic polypropylene (iPP) can result in macroscopic whitening, which originates from non-cohesive damage mechanisms, namely cavitation, at microscopic scale [1-2]. The formation of voids upon yielding has been well correlated with the negative pressure accumulated in the amorphous phase, and becomes significant with increasing inter- and intra-lamellar coupling [3]. Once nucleated, voids can grow with further increasing strain and result in severe volume dilatation, which in turn has significant impact on the fracture of isotactic polypropylene. Though the mechanism of void formation with respect to yielding has been addressed to a large extent, the relationship between void propagation and the intrinsic structure has not been elucidated yet. Our results indicate that the void propagation can be correlated with the properties of amorphous phase in isotactic polypropylene. Decreasing inter-chain sliding due to increasing entanglement density in the amorphous phase can suppress void propagation and thus volume dilatation to a large extent, which is the origin of the improved fracture strain and toughness.