Stabilization by hals and phenols in γ-irradiated polyproplyene

The γ-radiation initiated oxidation of polypropylene films and test strips has been studied both immediately after irradiation and also during post-irradiation accelerated aging at 60 degrees C. Stabilizers included blocked and unblocked phenols as well as secondary and tertiary hindered amines (HALS) including an oligomeric HALS. Oxidation product formation, yellowing and embrittlement (as measured in an instrumented bend test) have been compared with product formation. A partial correlation between suppression of oxidation during the irradiation step with long term, post-irradiation oven aging at 60 degrees C was found, but complicated by extensive destruction during irradiation of the active phenolic functionality in some additives, essential for peroxyl radical scavenging. Very long lifetimes with barely detectable yellowing were found for combinations of the amines with completely unhindered or only partially hindered phenols