Effect of Network Relaxation on Void Propagation and Failure in Isotactic Polypropylene at Large Strain

摘要

The important role of network relaxation in the voiding and fracture toughness of isotactic polypropylene (iPP) has been explored with video-aid tensile tests, two-dimensional small-angle X-ray scattering (2D-SAXS) measurements, and morphological observations. The results indicated that macroscopic volume dilatation related to voiding became lower during large deformation of iPP sample with rich gamma phase (denoted as gamma-iPP) cooled at 1 degrees C/min, compared with one with exclusive a form (referred to alpha-iPP) quenched in air. Furthermore, void propagation perpendicular to the tensile direction, demonstrated by Guinier approximation analysis of 2D-SAXS results, was suppressed to a large extent in such a gamma-iPP sample. Less network relaxation, resulted from its peculiar crystalline and amorphous phases, was responsible for lower volume dilatation and slower void propagation in the gamma-iPP sample. Meanwhile, less network relaxation and suppressed transverse void propagation contributed to higher toughness in the gamma-iPP sample.