The calorimetric signature of aging in an epoxy glass following mechanical rejuvenation*

Diglycidyl ether of bisphenol A (DGEBA) epoxy is cured with diethanolamine and then aged at 20°C below Tg for varying amounts of time. The samples are uniaxially compressed (“mechanically rejuvenated”) through yield and then further aged at room temperature. DSC temperature ramps are run on both (1) samples aged but not compressed and (2) samples aged after rejuvenation. Thermograms of samples aged at Tg-20°C exhibit the typical aging peak near or above Tg. It is found that compression erases the physical aging peak as expected from previous studies. The post-compression samples aged at room temperature show complex thermograms with a small “pre-Tg” peak and a broad “post-Tg” peak. Both of these peaks become more pronounced with increased post-rejuvenation aging time.