Structural relaxation of an epoxy resin at temperatures well below Tg. Issue 2 (11th December 2021) - Song, Hosup
Abstract: The effects of annealing a glassy polymer at temperatures well below T g on the dynamic linear viscoelastic properties were investigated. The polymer was an epoxy thermoset with a T g of 182°C. Specimens were annealed from 2 h to up to 600 h at temperatures from −100°C ( T g −282°C) up to T g . At annealing temperatures just below T g, there was no effect of annealing, and annealing at −100°C ( T g −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 ( T g −232°C) and 170°C ( T g −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 ( T g −132°C) and 100°C ( T g −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 T g 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 T g region. Abstract : Deep glass aging in an epoxy resin.