STRUCTURAL RELAXATION IN FULLY CURED EPOXY-RESINS

Enthalpy relaxation in a fully cured epoxy resin at 80 degrees C has been investigated in two different laboratories, the Universitat Politecnica de Catalunya and Aberdeen University, and using two different instruments (Mettler and Perkin-Elmer, respectively) for differential scanning 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 Narayanaswamy parameter, x, yields different values (0.45 from Catalunya and 0.39 from Aberdeen); similar differences are found for the non-exponentiality 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 similar activation energies. It is suggested that this results from a 'strengthening' due to the cross-linked epoxy network structure.