Thermal Rheological Analysis of Cure Process of Epoxy Prepreg

The cure process of epoxy prepreg used as composite pipe joints was studied by means of differential scanning calorimetry (DSC), Bohlin Rheometer and other techniques. Isothermal DSC measurements were conducted between 110 and 220 C, at 10 C intervals. The results show that the complete cure reaction could be achieved at 220 C. The isothermal cure process was simulated with the four-parameter autocatalytic model. Except in the late stage of cure reaction, the model agrees well with the experimental data, especially at high temperatures. To account for the effect of diffusion on the cure rate, a diffusion factor was introduced into the model. The modified model greatly improved the predicated data at the late stage of cure reaction. The dynamic cure process was different from the isothermal cure process in that it is composed of two cure reactions. For dynamic cure process, a three-parameter autocatalytic model was used. The parameters in the model were determined by two methods. One was based on Kissinger and Ozawa approach. The whole curing process was modeled with two reactions. Another method was based on Borchardt and Daniels kinetic approach with the whole curing process modeled with one reaction. The fitted results by the first and second methods agreed well with the experimental values in the late and early cure stages, respectively. Rheological properties of epoxy prepreg are closely related to the cure process. With the development of the cure reaction, gelation occurs and epoxy prepreg becomes difficult to process. As the temperature increases, the gel time decreases. Viscosity profiles were described by different models. Except for the first and nth order viscosity