Rejuvenation of epoxy glasses subjected to uniaxial compression

Two epoxy networks, differing significantly in their glass transition temperatures ( T gs), were subjected to uniaxial compression tests in the glassy state (20°C). One of the systems was based on the diglycidyl ether of bisphenol-A (DGEBA) cured with ethylenediamine (EDA). The other one was based on an epoxidized novolac (EPN) cured with 4,4′-diaminodiphenyl sulfone (DDS). Both systems were physically aged by specific thermal treatments. The endothermic enthalpy relaxation peak, characteristic of aged glasses, could be erased at temperatures well below T g by large mechanical deformations, i.e. close to the incipient strain hardening level in uniaxial compression tests. This phenomenon, which was accompanied by an increase in specific volume, constitutes a clear manifestation of rejuvenation produced by large mechanical stimuli. The validity of statements presenting an opposite point of view is also discussed.