Comparison of degradation behavior between soft and hard epoxy resins

Hiroyuki Ishii*, Naoshi Hirai, Yoshimichi Ohki

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


Soft and hard epoxy resins used as insulating sealants in nuclear power plants were aged simultaneously by heat and gamma rays at 80, 90, and 100°C, and the changes in their various properties induced as a result of their degradation were measured. The thermal, mechanical, dielectric, and spectroscopic properties hardly change in the hard epoxy resin, whereas they change drastically in the soft epoxy resin, indicating that the latter resin becomes hard and then brittle. This big difference in mechanical property between the two resins is attributable to a significantly low glass transition temperature of −30°C in the soft resin compared to that of 120°C in the hard resin. Although the hard epoxy resin with the high glass transition temperature exhibits thermal and mechanical properties insensitive to the aging conditions, its complex permittivity at temperatures higher than 140 °C shows an evident increase in accord with the progress of degradation. This phenomenon can be an indicator of the degradation of this resin. The effects of degradation on the absorption spectra in a THz frequency range are also examined.

Original languageEnglish
Pages (from-to)620-628
Number of pages9
JournalJournal of Nuclear Science and Technology
Issue number5
Publication statusPublished - 2021


  • Epoxy resin
  • degradation
  • electrical insulation
  • gamma radiation
  • glass transition temperature
  • nuclear power plant
  • temperature dependence

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Nuclear Energy and Engineering


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