STRUCTURAL RELAXATION IN FULLY CURED EPOXY-RESINS

Enthalpy relaxation in a fully cured epoxy resin at 80 degrees C has b een investigated in two different laboratories, the Universitat Polite cnica de Catalunya and Aberdeen University, and using two different in struments (Mettler and Perkin-Elmer, respectively) for differential sc anning calorimetry. The same values of activation energy (1100 kJ mol( -1)) and Delta C-p(0.34 J g(-1) K-1) were obtained in each laboratory. However, the peak-shift method for the evaluation of the Narayanaswam y parameter, x, yields different values (0.45 from Catalunya and 0.39 from Aberdeen); similar differences are found for the non-exponentiali ty parameter, beta (0.3 < beta < 0.456 from Catalunya and 0.456 < beta < 0.6 from Aberdeen). These discrepancies are tentatively attributed to differing thermal gradients in the two calorimeters. Nevertheless, the values of x appear high when compared with other glasses with simi lar activation energies. It is suggested that this results from a 'str engthening' due to the cross-linked epoxy network structure.