COMPARATIVE-STUDIES OF CHEMICAL-KINETICS OF AN EPOXY-AMINE SYSTEM

Chemical reaction kinetics of an aliphatic diepoxy-diamine system (DGE BD/4D) has been studied between 50 degrees C and 95 degrees C by two d ifferent calorimetric techniques; DSC in isothermal conditions on the one hand, conservation in thermostated tubes with successive extractio ns of samples studied by DSC in the dynamic temperature mode on the ot her hand. Experiments show that the kinetics determined by isothermal DSC are systematically faster than those obtained with the other techn ique, this advance starting during the initial phase of the reaction. We show that this gap comes from the mass difference between the sampl es used in the two techniques, and can be explained by two different r easons. On the one hand, there appears a delay in the attainment of th e thermal equilibrium at the beginning of the kinetics in the thermost ated tubes, the samples having a greater mass. On the other hand, expe riments have shown that there is a catalytic effect caused by the cont act of reactive system with air (probably due to the action of atmosph eric water). The area/volume ratio of samples being greater for sample s studied by isothermal DSC, the catalytic effect is favoured to a gre ater extent in the case of this technique, which induces a faster rate of reaction at the beginning of the kinetics. So, as the kinetic curv es x = f(t) have different forms, they are described by different kine tic models. The Spacek-model adequately describes the kinetic curves d etermined by isothermal DSC, with exponent values p = 1.20 and q = 0.4 5. The curves obtained by the technique of conservation in thermostate d tubes are well described by the second order autocatalytic model, th e ratio of the reactivities of primary and secondary amines having the value n = 1.1. Furthermore the T-g variation curve with the extent of reaction in the thermostated tubes agrees very well with the equation proposed by Pascault and Williams.