Isothermal cure of an epoxy system containing tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM), a multifunctional novolac glycidyl ether and 4,4'-diaminodiphenylsulphone (DDS): Vitrification and gelation

Times to gelation and vitrification have been determined at different isothermal curing temperatures between 200 and 240 degrees C for an epoxy/amine system containing both tetraglycidyl-4,4'-diaminodiphenylmethan (TGDDM) and a multifunctional Novolac glycidyl ether with 4,4'-diaminodiphenylsulphone (DDS). The mixture was rich in epoxy, with an amine/epoxide ratio of 0.64. Gelation occurred around 44% conversion. Vitrification was determined from data curves of glass transition temperature, T-g, versus curing time obtained from differential scanning calorimetry experiments. The minimum and maximum values T-g determined for this epoxy system were T-g0 = 12 degrees C and T-gmax = 242 degrees C. Values of activation energy for the cure reaction were obtained from T-g versus time shift factors, a(T), and gel time measurements. These values were, respectively, 76.2 kJ mol(-1) and 61.0 kJ mol(-1). The isothermal time-temperature-transformation (TTT) diagram for this system has been established. Vitrification and gelation curves cross at a cure temperature of 102 degrees C, which corresponds to glass transition temperature of the gel.