Models of reaction commonly employed in the curing of thermosetting resins

Abstract

In order to study the kinetics of the complex curing processes of thermoset resins, the rate of reaction dα/d t at constant temperature is related to some function of the reaction f(α). Two empirical kinetic functions f(α) are usually used: nth-order kinetics ( f(α) = (1 −α) n ) where α is the degree of conversion and n is a reaction order, and autocatalyzed reaction kinetics (such as f(α) = α m (1−α) n ) where m is also a reaction order. Applying both models to data obtained with isothermal experiments, we can obtain the kinetic parameters n and m, the rate constant k and, assuming that its temperature dependence is an Arrhenius-type equation ( k = A exp(− E/ RT)), the activation energy of the process ( E) and the frequency factor ( A). Despite some criticism with regard to the mechanistic interpretation, both models are also applied to non-isothermal experiments. In this paper we present studies that we have made in order to simulate the curing process of unsaturated polyesters with both nth-order and autocatalyzed kinetics and for isothermal and non-isothermal processes. In the isothermal process, we solved the kinetic equations in order to determine α and dα/d t as a function of time and also to obtain the heat generation curve (d H/d t) as a function of time. In the non-isothermal process we solved the kinetic equations in order to obtain α, dα/d t and d H/d t as a function of temperature.