The breakage of original crystallites determined small strain cavitation in syndiotactic polypropylene during step-cycle tensile deformation

Abstract

The step-cycle tensile experiments were carried out on syndiotactic polypropylene to explore the crystallization and deformation temperature dependency of cavitation via the wide and small angle scattering X-ray techniques. The development of cavitation process exhibited a dependency on the original crystallites. The cavities appeared around the yield point could be healed after releasing the tensile force before a specific strain, while the ones occurred beyond this point are permanent. This phenomenon was in accord with the process of the recoverable lamellar thickness within one stretching and relaxation cycle. After reaching the critical point of fragmentation and recrystallization of lamellae, the growth rate of cavities started to decrease due to the destruction of the original crystallites. Moreover, the crystallites formed at higher crystallization temperature could be preserved to a larger strain and thus more intense cavitation could be expected. The high deformation temperature could weaken the intensity of cavitation, then, the weakest cavitation phenomenon was observed in the sample crystallized at low temperature but drawn at high temperature.