Thermal and UV degradation of polypropylene with pro-oxidant. Abiotic characterization

The oxodegradation of an injection molding grade polypropylene (PP), formulated with 0%, 1.5%, and 3% w/w of a pro-oxidant additive, was studied. The degradation was conducted in a weathering tester at 60 degrees C for 40 h. The process was monitored by Fourier transform infrared spectroscopy, standard differential scanning calorimetry, and successive self-nucleation and annealing. Neat PP samples did not exhibit significant changes during the exposure time employed. PP samples with oxo-additive presented similar changes independently of the amount of oxo-degradative additive employed; however, the changes manifested more rapidly in the formulation with higher pro-oxidant content. Fourier transform infrared spectroscopy studies revealed the presence of hydroxyl and carbonyl functional groups whereas differential scanning calorimetry tests showed the decrease in the melting and crystallization temperatures as a consequence of the chain scission and oxidation reactions taking place during exposure. In addition, the induction time (t(id)) of the oxo-degradative process was determined for each technique employed and successive self-nucleation and annealing was found to be the most sensitive characterization technique to reveal structural modifications in PP samples. (C) 2017 Wiley Periodicals, Inc.