PHOTOCROSSLINKING OF POLYETHYLENE .3. THERMAL OXIDATIVE STABILITY OF PHOTOCROSSLINKED POLYETHYLENE

The thermal oxidative stability of photocrosslinked high density polyethylene was studied. The relative effectiveness of various antioxidants (hindered phenols and amines, aromatic amine, organic sulfides, and phosphites) was examined by comparing the oxidation induction time (OIT) which was measured using differential scanning calorimetry. Hindered phenol antioxidants were found to be most effective. At an antioxidant concentration of 0.20 wt % which gave an OIT value of 20 min at 200°C, the photocrosslinking rate was decreased only to a limited extent as evidenced by a small drop in gel content. However, the efficiency of the antioxidants as stabilizers decreased to a considerable extent after the photocrosslinking process. Serious surface deterioration was found which was ascribed to depletion of antioxidant at the surface mainly due to high rate of oxidation and evaporation. Copyright © 1990 John Wiley & Sons, Inc.