Micro-structure of gamma-ray irradiated polyethylenes studied by positron annihilation |
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| Institution: | 1. Department of Orthopedic Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea;2. Department of Orthopedic Surgery, Seoul National University College of Medicine, Seoul, Republic of Korea;1. Department of Endocrinology, Diabetes and Metabolism, Christian Medical College, Vellore, Tamil Nadu, India;2. Department of Endocrinology & Metabolism, All India Institute of Medical Sciences, Bilaspur, Himachal Pradesh, India;3. Dept. of Biostatistics, Christian Medical College, Vellore, Tamil Nadu, India;4. Dept. of Hepatology, Christian Medical College & Hospital, Christian Medical College, Vellore, Tamil Nadu, India;1. Department of Medicine, McGill University, Montréal, Québec, Canada;2. CaMos National Coordinating Centre, McGill University, Montréal, Québec, Canada;3. Department of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada;4. Centre of Bone Diseases, Lausanne University Hospital, Lausanne, Switzerland;5. Division of Epidemiology and Community Health, University of Minnesota, Minneapolis, MN, USA;6. Department of Medicine, University of Calgary, Calgary, Alberta, Canada;7. Faculty of Medicine, Memorial University, St. John''s, Newfoundland, Canada;8. Department of Medicine, University of British Columbia, Vancouver, BC, Canada;9. Department of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada;10. Saskatoon Osteoporosis and CaMos Centre, Saskatoon, Saskatchewan, Canada;11. Department of Medicine, University of Toronto, Toronto, Ontario, Canada;12. Department of Medicine, McMaster University, Hamilton, Ontario, Canada |
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| 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 I3 and the lifetime τ3 of the longest lived component was significant below the glass transition temperature Tg, while they were little affected above Tg. For LDPE a marked minimum was observed in the I3 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 I3 and τ3 decreased on irradiation mainly due to radiation induced free radicals. The gel fraction of HDPE was small when irradiated below Tm, while it rose sharply on irradiation near Tm. Positron lifetime parameters of this highly crosslinked HDPE showed a distinct difference compared to HDPE irradiated below Tm. Usefulness of the positron annihilation method is discussed in conjunction with studying micro-structure of polymers. |
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