A critical molar mass separating the ductile and brittle regimes as revealed by thermal oxidation in polypropylene

The thermal oxidation of unstabilized polypropylene films has been studied at 70, 90, 110 and 130 °C in air by IR, SEC, rheometry and tensile testing. Embrittlement is observed when the weight average molar mass reaches 210±10 kg mol−1. Polydispersity data are consistent with a homogeneous random chain scission process. This especially high sensitivity of fracture properties to chain scission is assumed to be specific of semi-crystalline polymers having their amorphous phase in rubbery state.