The fracture behavior of particle modified polypropylene - 3D reconstructions and interparticle distances

The fracture behavior and fracture mechanics at the very early stages of both ethylene-propylene-rubber (EPR) and linear low-density polyethylene (LLDPE) modified isotactic polypropylene (iPP) were investigated. For this purpose tensile tests of the respective samples were stopped at forces far below the yield point and subsequently 3D reconstructions of the fracture regions were performed. It was thus possible to obtain information about the distribution of the surface-to-surface interparticle distances of the EPR and LLDPE particles, the size of voids and cracks/crazes and also their position with respect to the EPR and LLDPE particles. A single quantitative parameter was introduced that characterizes the correlation between the interparticle distance and the formation of cracks/crazes. Whereas crack/craze formation occurred in EPR modified iPP, LLDPE modified iPP showed debonding of the particles from the matrix and cavitation. But despite the completely different fracture mechanisms, the surface-to-surface interparticle distance distribution, particle agglomeration and thus percolation theory seem to play a vital role in both cases, at least at the start of fracturing, confirming theories developed by Wu and Liang.