The Time-Temperature-Transformation (TTT) Cure Diagram of Thermosetting Systems.
Abstract:
An isothermal time-temperature-transformation TTT cure diagram for thermosetting systems has been developed to aid in the understanding of the cure process and the properties after cure. The diagram summarizes in a convenient manner the temperature of cure T sub cure vs. the times to gelation, vitrification, phase separation in the case of rubber-modified systems, full cure, and thermal degradation. A more complete diagram could also include contours of constant conversion, viscosity, and modulus. The principal experimental technique which has been used to obtain a TTT diagram, torsional braid analysis TBA, is described. Two recent models describing the cure process are reviewed from these the time to vitrification vs. T sub cure is computed from the chemical kinetics and the conversion at vitrification. One model uses a relationship between T sub g and the extent of conversion at vitrification in conjunction with experimental data for the extent of conversion at vitrification, whereas the other predicts the extent of conversion of T sub g from relationships in the literature. Both models predict an S-shaped time to vitrification curve, as has been obtained experimentally. The second model has been applied also to linearly polymerizing systems.