Effect of the initiator content and temperature on the curing of an unsaturated polyester resin

Abstract

The influence of temperature and the initiator concentration on the curing of an unsaturated polyester resin was studied by means of differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). It was established that there is an isoconversional relationship of the type Int = a - bln[I] 0 between the curing time, t, and the initial initiator concentration, [I] 0 , at a given temperature. This relationship indicates that the degree of conversion curves vs. the logarithm of the curing time at different [I] 0 may be superposed by displacement relative to a reference curve. It was confirmed that the reaction mechanism varies throughout the whole curing process, although it does not vary with the temperature and the [I] 0 at each degree of conversion. It was established that there is a universal isoconversional relationship of the type Int = d - bln[I] 0 + E/RT that expresses the dependency of the curing time on the temperature, T, and the [I] 0 . The parameters a, b, and d depend on the reaction mechanism, and can be calculated on the basis of isothermal experiments at different temperatures and with different [I] 0 . The adjustment Int = d - bln[I] 0 + E/RT shows that there is an equivalence between the effect on the curing kinetics of the temperature and the initiator concentration. The same curing process can be achieved by using different combinations of curing temperatures and the [I] 0 . In the two adjustments established, it is not necessary to know the reaction mechanism, and the only assumption made is that for a given conversion the reaction mechanism is invariant with respect to the [I] 0 and the temperature.