INFLUENCE OF THE ACCELERATOR CONCENTRATION ON THE CURING REACTION OF AN EPOXY-ANHYDRIDE SYSTEM

The effect of accelerator content on the curing reaction of an epoxy r esin based on diglycidyl ether of bisphenol A (DGEBA) with methyl-tetr ahydrophthalic anhydride was studied by DSC. The uncatalysed curing oc curs at high temperature (between 190 and 310 degrees C) with thermal degradation. The addition of accelerator which is a tertiary amine cat alyst agent, namely dimethylbenzylamine (DMBA), causes two exothermic peaks. The cure extent and the position of the peaks depend on the acc elerator content, The first peak, which is sharp and well defined, app ears between 80 and 200 degrees C and may be attributed to the catalys ed curing. The second peak, which is broad, only appears for low accel erator content (lower than 1 pbw) in the zone of uncatalysed curing (b etween 200 and 320 degrees C), and may be attributed to the uncatalyse d curing. The activation energy corresponding to the first exothermic peak in the catalysed curing, calculated by the Kissinger method, decr eases with the accelerator content. Kinetic analysis performed by Male k's method shows that the autocatalytic model (two-parameter Sestak-Be rggren equation) can describe satisfactorily the kinetics of the catal ysed and uncatalysed curing. In the catalysed system, the parameters m and n increase slightly with the accelerator content, and the pre-exp onential factor. In A, undergoes a slight decrease. The maximum T-g of the fully cured epoxy obtained by isothermal curing at 110 degrees C in catalysed systems shows no significant changes. These results mean that the differences observed in the kinetics of curing between cataly sed systems do not imply significant changes in the structure of the n etwork of the epoxy resin.