Vitrification and further structural relaxation in the isothermal curing of an epoxy resin

Isothermal curing of a DGEBA epoxy resin with a hardener derived from phtalic anhydride was performed at temperatures T c between 30 and 130°C. The structural relaxation process was found to begin at higher curing times (t c ) when T c decreases because the vitrification of the systems starts later. Both the enthalpy recovery and the temperature of the endothermic peak increase with the annealing time, calculated as the difference between t c and the time in which vitrification occurs, and tend tohave a limiting value.