A new method for the determination of the Arrhenius constants for the cure process of unsaturated polyester resins based on a mechanistic model

Abstract

Abstract Several models have been proposed to describe the kinetic behaviour of the cure of unsaturated polyester (UPs) resins as manifest by thermal data measurements. Ozawa proposed a method for the estimation of the overall Arrhenius constants for the cure process from an empirical rate expression which describes the relationship between the heating rate and the time taken to reach the maximum cure rate for data generated by various thermal analytical methods. This approach has been extended so as to be applicable to a realistic mechanistic kinetic model of the cure of UP resins in which diffusion-limited propagation and decreasing initiator efficiency with conversion are involved. The procedure was tested with a commercial UP resin system using dynamic DSC methods for the measurement of cure. The DSC measurements have indicated that the diffusion-limited period of cure only starts after the point of maximum reaction rate has been reached and, thus, the true propagation rate constant can be evaluated from DSC data up to that point without having to consider the effects of radical trapping processes or decreasing initiator efficiency in this particular case. The values of the activation energy and the frequency factor found were 23,590 J mol−1 and 6.78 × 105 dm3 mol−1 min−1, respectively. The technique is independent of experimental baseline accuracy and the total heat of cure. Moreover, unlike the time-consuming procedure of curve fitting over the whole conversion range which has been adopted previously to obtain multiple unknowns, this approach results in rapid, highly convergent parameter optimisation.