The kinetic analysis of isothermal curing reaction of an unsaturated polyester resin: Estimation of the density distribution function of the apparent activation energy

The kinetic process of isothermal curing of an unsaturated polyester resin samples has been studied. The differential isoconversional method is used to yield dependency of the apparent activation energy, Ea, on the degree of cure. It was found that the dependence of Ea on α is complex, but in the conversion range α = 0.10–0.50, Ea is practically constant. It was found that the gelling stage of curing process is mainly controlled chemically which can be best described by two-parameter autocatalytic model. At higher values of α, when vitrification point is reached, the change in rate-limiting step was observed. As the consequence of shifting effect from the kinetics to diffusion control, the kinetic law equation is modified with additional diffusion term. It was found that the experimentally obtained density distribution function of the apparent activation energy can be approximate by unbalanced modified Gaussian distribution function with quite satisfactory precision.