Abstract
Effects of gamma-ray irradiation on high density (HDPE) and low density (LDPE) polyethylenes were measured by positron annihilation at temperatures between 100 and 420 K. The effect of the irradiation on the intensity I 3 and the lifetime τ 3 of the longest lived component was significant below the glass transition temperature T g, while they were little affected above T g. For LDPE a marked minimum was observed in the I 3 vs T curve. The lower edge of the minimum, corresponding to glass II and glass I transitions, was found to shift to lower temperatures by the irradiation. In HDPE both I 3 and τ 3 decreased on irradiation mainly due to radiation induced free radicals. The gel fraction of HDPE was small when irradiated below T m, while it rose sharply on irradiation near T m. Positron lifetime parameters of this highly crosslinked HDPE showed a distinct difference compared to HDPE irradiated below T m. Usefulness of the positron annihilation method is discussed in conjunction with studying micro-structure of polymers.
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Schedule a callMore From: International Journal of Radiation Applications & Instrumentation. Part C, Radiation Physics & Chemistry
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