Hot air aging behavior of polypropylene random copolymers

This article deals with the global aging behavior of three polypropylene random copolymer (PP-R) materials with varying primary structure and morphology. Hot air aging experiments at elevated temperatures from 95 to 135 degrees C were carried out using micro-sized specimens with a thickness of 100 mu m. Technological and analytical aging indicators were monitored for an exposure time of up to 750 days. Independent of comonomer type (ethylene vs. butylene) and morphology (alpha vs. beta crystal form) a critical molar mass of 300 kg mol(-1) was obtained. The consumption of antioxidants was slower for the beta-nucleated PP-R grade with finer spherulitic structure. The beta-grade outperformed the alpha-crystal PP-R grades resulting in about 20% higher time-to-embrittlement values. (C) 2018 Wiley Periodicals, Inc.