1. Structural relaxation of an epoxy resin at temperatures well below Tg*.
- Author
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Song, Hosup, Medvedev, Grigori A., and Caruthers, James M.
- Subjects
EPOXY resins ,HEAT capacity ,TEMPERATURE - Abstract
The effects of annealing a glassy polymer at temperatures well below Tg on the dynamic linear viscoelastic properties were investigated. The polymer was an epoxy thermoset with a Tg of 182°C. Specimens were annealed from 2 h to up to 600 h at temperatures from −100°C (Tg −282°C) up to Tg. At annealing temperatures just below Tg, there was no effect of annealing, and annealing at −100°C (Tg −282°C) showed no difference between 2 and 6 h annealing, although annealing effects might be seen at longer times. At temperatures between −50°C (Tg −232°C) and 170°C (Tg −12°C) the storage isotherms increased with annealing while the loss isotherms decreased. In addition, the heat capacity as measured via DSC after annealing at 50°C (Tg −132°C) and 100°C (Tg −82°C) exhibited endothermic peaks approximately 40°C above the annealing temperature. This study clearly shows that a material deep in the glassy state is not frozen, but undergoes continuing evolution. The nature of deep glass aging is different than physical aging in the Tg region, where deep in the glass the relaxation spectrum changes magnitude and shape but does not shift along the log frequency axis in contrast to physical aging in the Tg region. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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