Fracture Mechanics Properties of Polymorphic Polypropylene

Polypropylene (PP) is a widely used thermoplastic and polymorphic polymer. Three different types of PP were prepared, namely non-nucleated, α- and β-nucleated PP. These materials were pressed using different cooling rates to influence the degree of crystallinity χ within the materials, which was determined by differential scanning calorimetry (DSC). The materials resistance against stable crack propagation was described by R-curves. The Jd–Δa curves were determined using the instrumented Charpy impact test (ICIT) to apply single edge notch bending specimens (SENB) with a high loading velocity. The results show not only the influence of the cooling rate on the degree of crystallinity but also a correlation between the degree of crystallinity and the materials resistance against stable crack propagation. The lower the cooling rate of the material is the higher is the degree of crystallinity and the higher seems to be the materials resistance against stable crack propagation.