Cavitation behavior of polypropylene/polyethylene multilayer films during uniaxial tensile deformation: In-situ synchrotron X-ray study

Abstract

The cavitation of melt-coextruded multilayer films of alternated polypropylene (PP) and polyethylene (PE) during the uniaxial tensile deformation has been investigated. The initiation and evolution of cavities and the relationship between cavitation and plastic deformation have been studied via in-situ SAXS and WAXS techniques. The critical strain for the initiation of cavitation (εcav), crystal shear (εCSh), and yield (εyield) have been estimated from the in-situ experiments. The results show that the sequence of deformation is crystal shear, cavitation and yield, i.e. εCSh<εcav<εyield, indicating that crystal plastic deformation occurs before the cavitation and yield. Additionally, the layer numerosity and annealing temperature (Tanneal) have been discovered to not only modify the mechanical behavior but also regulate cavitation by changing the initial microstructure. The samples with less layer numerosity and high Tanneal improve the macroscopic mechanical strength, whereas the increase of layer numerosity can reduce the stress of cavitation onset (σcav) and retard the onset of cavitation onset (high εcav value). The current study is significant in elucidating the internal mechanism of stretch-induced cavitation behavior in multilayer films.