Mechanisms of antioxidant action: effect of processing conditions on the stabilizing effectiveness of metal xanthates and related dixanthogen in polypropylene

The effects of processing conditions, on the thermal and photo-oxidation of polypropylene containing different metal octyl xanthates (MOX) and the related dixanthogen (OX) have been examined. It is concluded that in the presence of a limited amount of oxygen the metal xanthates (e.g. nickel and cobalt) are better u.v. stabilizers than the dixanthogen, and their greater effectiveness is atrributed to a combination of complementary mechanisms, i.e., peroxide decomposition, u.v. absorption, u.v. screening and radical scavenging. Under severe processing conditions (excess oxygen), the activity of the metal xanthates is reduced and their effectiveness becomes very similar to that of the corresponding dixanthogen in both melt and u.v. stabilization. The main mechanism of action in this case is peroxide decomposition.