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 stab ilities of phenolic antioxidant/phosphite combinations has been determined in HDPE by using FTIR analysis. The results show that while under thermal a ging the effects are generally antagonistic, under photooxidation the effec ts 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 oxidati on, while under light they could cause stabilization. Derivative UV and FTI R analysis on pre-melt blends of the additives in solution shows evidence f or strong complexation for the phosphite antioxidants. Other acid scavenger s such as hydrotalcite and calcium stearate also appear to influence the be havior of phenolic antioxidants in thermal oxidation. The antagonistic effe ct of zinc stearate was also confirmed following a single pass in an extrud er, where for all formulations there was a greater reduction in MFI associa ted with crosslinking.