Thermal degradation of high-impact polystyrene with pro-oxidant additives

The oxo-degradation process of high-impact polystyrene (HIPS) with 0, 1.5 and 3% w/w of pro-oxidant d2w® was studied. The degradation was conducted in a convection oven employing temperatures of 50, 55, 60 and 65 °C. The process was monitored by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests (i.e., strain at break). Neat HIPS samples did not exhibit significant changes for all conditions evaluated. Samples with oxo-additive exhibited a complex behavior in relation to the rate of degradation; HIPS with 1.5% oxo-additive exhibited faster degradation than samples with 3% oxo-additive at temperatures of 50 and 55 °C, but no significant differences at 60 and 65 °C. FTIR studies showed the evolution of hydroxyl and carbonyl functional groups during degradation and allowed to infer that polybutadiene phase is degraded preferentially. A complete loss of mechanical properties of samples with pro-oxidant was observed with changes occurring faster as temperature increased. Tensile and DSC tests were the most effective techniques for monitoring the degree of decomposition of HIPS, since the results obtained evidenced early structural changes during thermal aging that were undetected by FTIR and TGA at identical exposure times.