Performance and antioxidant activity of phenol/phosphite antioxidants in synergistic blends in the thermal and photooxidation of high-density polyethylene (HDPE) film: Influence of zinc stearate

The influence of zinc stearate (ZnSt) on the thermal and photochemical stabilities of phenolic antioxidant/phosphite combinations has been determined in HDPE by using FTIR analysis. The results show that while under thermal aging the effects are generally antagonistic, under photooxidation the effects are synergistic. The Interactions appear to be dominated by the role of complex formation between the phosphites and ZnSt. Such inter-actions would remove the hydroperoxide effectiveness of the phosphite in thermal oxidation, while under light they could cause stabilization. Derivative UV and FTIR analysis on pre-melt blends of the additives in solution shows evidence for strong complexation for the phosphite antioxidants. Other acid scavengers such as hydrotalcite and calcium stearate also appear to influence the behavior of phenolic antioxidants in thermal oxidation. The antagonistic effect of zinc stearate was also confirmed following a single pass in an extruder, where for all formulations there was a greater reduction in MFI associated with crosslinking.