AbstractStandardized mixtures of powdered polyethylenes and lead peroxide constitute redox systems that ignite upon the surface of a hot plate after a time interval that is inversely related to temperature and to the oxidizability of the resin. The influence of antioxidants and of oxidation accelerators upon the lead peroxide ignition is identical with that upon the reaction of polyethylenes with oxygen gas at elevated temperatures. Methyl branching also has an identical effect on both reactions. Hence, plots of ignition time versus ignition temperature serve to characterize the oxidative reactivity of polyethylene resins. This solid–solid redox system is shown to have long shelf stability at room temperature, not to be subject to premature ignition induced by the presence of more easily oxidized contaminants, and to suffer the effect of carbon black filler by showing a more sluggish reactivity. The lead peroxide ignition test serves to distinguish among polyethylenes. It can be used to assay the antioxidative proclivities of antioxidants. It can be substituted for electrical dissipation factor measurements in following the hot mill oxidation of polyethylenes. Since this test differentiates among polyethylenes having identical melt indices, lead peroxide ignition time values can also provide a useful specification parameter in describing polyethylene resin
展开▼
