Threading the Needle: Achieving High Glass Transition Temperature and Toughenability in Epoxy Resins
Balancing high glass transition temperature (Tg) and crack-propagation resistance is a well-known dilemma in epoxy thermosets used for high-performance composite applications ranging from automotive to aerospace. Thermoset polymers with tightly formed 3D crosslinked structures are characterized by restricted long chain molecular movement, which can delay the onset of glass transition and extend the service temperature. However, when such thermosets are subject to an impact, the plastic deformation is confined at the crack tip by the tightly crosslinked network, resulting in minimal fracture toughness that is not improved significantly even with rubber toughening. In this work, we study the effect of using an isocyanate modified bisphenol A diglycidyl ether epoxy resin comprised of epoxy-terminated oxazolidone ring structure on the Tg and toughenability of bifunctional epoxy resins. Specifically, we will investigate the hypothesis that incorporation of the modified epoxy may enable enhanced toughenability through an increase in chain length between the crosslinks while also providing sufficient molecular rigidity for superior Tg performance due to the oxazolidone ring in the backbone structure. Preliminary results show the toughened thermoset containing the modified epoxy exhibits up to 250% improvement in fracture energy (GIC) with Tg of 200 °C.
Authors: Y.L. Liang, and P. Badrinarayanan
Conference: SAMPE Seattle 2017