Thermoset Polymers Characterization as a Function of Cure State Using Off-stoichiometry Proxies

Rapid reaction kinetics often produce drastic changes in the thermo-chemo-mechanical characteristics of thermoset polymers over short time periods. Thus, it is a major challenge to quantify material properties over the entire spectrum of cure states at relevant temperatures with both efficiency and accuracy. This work presents a novel characterization technique as a function of the cure state of a difunctional epoxy with amine curing agent through off-stoichiometry mixing formulations that serve as proxies for the intermediately crosslinked polymer. Mass density, cure kinetics, and elastic and strength properties are characterized across four mixing ratios, and relative cure/crosslinked states of off-stoichiometry cases are quantified. Essential to this unique approach is the capability to eliminate time dependence resulting from reaction kinetics on characterizing intermediate crosslinking states. The procedure reported herein facilitates efficient and accurate measurement of properties of curing epoxies for building and validating computational process modeling frameworks developed for optimizing material performance.