Time‐dependent changes in mechanical properties of neat and reinforced epoxy resins

Several neat and reinforced epoxy resin formulations were prepared and investigated. Solid glass microspheres, with and without coupling agent, were used as reinforcement. After completion of post‐cure all samples were quenched into an ice‐water bath. Upon removal from the ice‐water bath, dynamic mechanical and fracture properties of all samples were evaluated as a function of time elapsed after quenching. Electron microscopic evidence was obtained for the existence of nodular morphology in all cured systems. The changes in dynamic mechanical and fracture parameters, induced by the sub‐T_g annealing, were described in terms of the model of inhomogeneous thermoset morphology.