Rheological Characterization of Thermoset Materials

Thermosets are polymeric materials that solidify irreversibly due to cross-linking that occurs between molecules. The solidification process of thermosets is dominated by an exothermic reaction called curing, which can be activated by heat, mixing, or both. As curing, and cross-linking, progresses through the material, the viscosity of the thermoset increases due to the emerging molecular network, and, conversely, less mobility of the individual molecules. Sheet Molding Compounds (SMC) are thin sheets of semi-finished composites consisting of uncured thermosetting matrix and discontinuous fibers. Usually, SMC is processed in compression molding, in which the material is subjected to heat and compression while in a mold to achieve the desired part shape, then, as curing progresses, the part is removed and allowed to cool. As such, variables such as peak curing temperature, viscosity, storage/loss modulus, pressure profile, among others, are of importance to understand what occurs during the processing and manufacturing of the material. The focus of the study lies in understanding these variables and intrinsic material properties of thermosets to predict how the material would behave during manufacturing. The first phase of the project will focus on the curing reaction and understanding the degree of curing and, eventually, its effects on other variables. Differential Scanning Calorimetry (DSC) will be utilized to evaluate the curing degree and estimate curing conditions of the material. These experiments will elucidate how the temperature dependence of the cure affects other processing parameters.