Experimental modeling of the cure behavior of a formulated blend of DGEBA epoxy and C12-C14 glycidyl ether as a reactive diluent

Abstract

Microwave curing of polymer matrix composites has been suggested as an attractive substitute for conventional thermal curing. Formulations of epoxy and reactive diluents have the advantage of better wettability and uniform fiber impregnation. However, higher peak exotherms in large masses, and thus thermal overshoot, presents a challenge for cure cycle optimization. Therefore, building a reliable curing model will not only predict the behavior of these materials during actual processing, but also facilitate numerical modeling of the process and comparison of other resin formulations. In this study the effect of the reactive diluent on the isothermal cure kinetics of low viscosity epoxy was investigated using differential scanning calorimetry (DSC). A formulated blend of diglycidyl ether of bisphenol A (DGEBA) and C12–C14 aliphatic glycidyl was cured using diethylene triamine as the curing agent. Using a standardized procedure, ISO 113571-5, the epoxy formulation was isothermally cured at several temperatures and the heat flow monitored and recorded. Using the heat flow data from DSC, the rate of cure was determined experimentally and a proper autocatalytic model with a total order of about 2.3 was fit to describe the process. Least-square regression and isoconversion methods were used to find the model parameters and the activation energy, respectively. The accuracy of the model shows fine correlation with experimental data. By comparison to other epoxy resin without diluents, the analysis of the data shows that the reactive diluent increased the curing rate, while the values of activation energy and process parameters remained within the typical values of epoxy formulations. Based on these data, the future use of these types of resins in nonthermal curing of epoxy matrix composites is discussed. POLYM. COMPOS., 26:593–603, 2005. © 2005 Society of Plastics Engineers