REJUVENATION OF EPOXY GLASSES SUBJECTED TO UNIAXIAL COMPRESSION

Two epoxy networks, differing significantly in their glass transition temperatures (T(g)s), were subjected to uniaxial compression tests in the glassy state (20 degrees C). One of the systems was based on the d iglycidyl 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 b y specific thermal treatments. The endothermic enthalpy relaxation pea k, characteristic of aged glasses, could be erased at temperatures wel l below T-g by large mechanical deformations, i.e. close to the incipi ent strain hardening level in uniaxial compression tests. This phenome non, which was accompanied by an increase in specific volume, constitu tes a clear manifestation of rejuvenation produced by large mechanical stimuli. The validity of statements presenting an opposite point of v iew is also discussed.