Electron Microscopic Study of the Morphology of Cured Epoxy Resin

摘要

An electron microscopic study of fracture surfaces and microtomed sections of a cured epoxy resin based on the difunctional Bisphenol-A type resin cured with different amounts of metaphenylene diamine is presented. Heterogeneities in the 5-100 nm range are seen to be present and have relatively higher crosslink density compared to the surrounding matrix. It is observed that the fracture path is around the heterogeneity and not through it. The size of the heterogeneity is a function of the curing agent concentration and also of the cure cycle. The stoichiometric sample, which has the highest crosslink density and the highest glass transition temperature, has the smallest heterogeneities. On either side of stoichiometry, the heterogeneity size increases. The samples subjected to a more severe postcuring cycle have much larger heterogeneities. The possible physical basis for these differences is discussed.