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International Journal of Polymer Science
Volume 2017, Article ID 1362491, 10 pages
https://doi.org/10.1155/2017/1362491
Research Article

Discoloration Effects of High-Dose γ-Irradiation and Long-Term Thermal Aging of (U)HMW-PE

1Bundesanstalt für Materialforschung und -prüfung (BAM), 12200 Berlin, Germany
2Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), 12489 Berlin, Germany

Correspondence should be addressed to Matthias Jaunich; ed.mab@hcinuaj.saihttam

Received 21 February 2017; Revised 20 June 2017; Accepted 5 July 2017; Published 6 September 2017

Academic Editor: Robert A. Shanks

Copyright © 2017 Anja Kömmling et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Two polyethylene types with ultra-high (UHMW-PE) and high molecular weight (HMW-PE) used as neutron radiation shielding materials in casks for radioactive waste were irradiated with doses up to 600 kGy using a 60Co gamma source. Subsequently, thermal aging at 125°C was applied for up to one year. Degradation effects in the materials were characterized using colorimetry, UV-Vis spectroscopy, IR spectroscopy, and DSC. Both materials exhibited a yellowing upon irradiation. The discoloration of UHMW-PE disappeared again after thermal aging. Therefore, the yellowing is assumed to originate from annealable color centers in the form of free radicals that are trapped in the crystalline regions of the polymer and recombine at elevated temperatures. For the antioxidant-containing HMW-PE, yellowing was observed after both irradiation and thermal aging. The color change was correlated mainly to decomposition products of the antioxidant in addition to trapped radicals as in UHMW-PE. Additionally, black spots appeared after thermal aging of HMW-PE.