(598d) Thermoset Curing Schedule and Its Affect on the Final Properties

Most thermoset resin manufacturers recommend a two temperature step cure schedule. The first temperature step generates the cross linking sites (or nodes) and prevents the sample from decomposing. The second temperature step binds the nodes together into a highly cross linked material. The material is not as susceptible to decomposition after the first step. This curing schedule gives a material with maximum cure and physical properties such as: modulus, thermal stability and delamination. A process engineer, striving to minimize the time in process, may decide to shorten, or eliminate, the first temperature step. Although this shortens the process time, it can have serious impact on the final properties of the material. Measuring the final modulus of the cured specimen at room temperature is a good measure of the final cure state of the specimen. Since most of the commercial processes use large batches, it is not economically feasible to run large batches of test cure schedules. The average Dynamic Mechanical Analyzer (DMA) is ideally suited to measuring the modulus during the cure, but the sample's stiffness becomes too large for the DMA to measure the same cured specimen back at room temperature. The DMA/SDTA 861 is capable of measuring the shear modulus of a thermoset resin from the uncured state to the cured state, at high temperature, and the cured state back at room temperature. This paper will report the results of these tests as the cure schedule is changed.