Performance of vitamin E/phosphite antioxidant stabiliser formulations for polypropylene during multi-pass extrusion processing

The processing stabilisation efficacy of Vitamin E/phosphite antioxidant combinations via multi-pass extrusion has been undertaken in polypropylene.Stabilisation was monitored through colour (yellowness Index) and melt flow index by selecting two phosphite stabilisers, Alkanox P-24 and P-240.A phenolic antioxidant, Anox 20, was used as a reference processing standard.Five multi-pass extrusions were performed on the Vitamin E/phosphite package combinations at 500 and 100ppm levels and Anox 20 control covering the range 0-100% w/w.From melt flow index analysis, significant synergistic stability improvements were obtained and outperformed the conventional phenolic Anox 20 antioxidant combinations under multi-extrusion conditions.In contrast, the Vitamin E/phosphite combinations were poor as long-term heat ageing stabilisers.This may be due to the higher volatility of Vitamin E over longer-term ageing.However, colour reduction was observed at low Vitamin E concentrations of less than a 10:90 ratio with the phosphites.No colour protection above the 10:90 ratio was observed, although interestingly, above the ratio of 20:80, increased colour plateued.One important finding is the observed high melt flow index stability of the Vitamin E formulations at low concentrations