The effect of stoichiometry and thermal history during cure on structure and properties of epoxy networks

摘要: Abstract An investigation was carried out into the effect of amine/epoxy stoichiometry and thermal history during cure on physical mechanical properties epoxy networks. The formulation studied consisted a diglycidyl ether bisphenol A resin 4,4′-diaminodiphenyl sulfone curing agent. experimental matrix based upon three ratios seven different histories cure. Techniques used included dynamic fracture analysis, Fourier transform infra-red (FTi.r.) spectroscopy. highest glass transition temperature (Tg) observed in stoichiometric lowest epoxy-rich mixture. For given stoichiometry, value Tg, infinity not function except, interestingly, case when initial 180°C. rubbery state modulus average molecular weight between crosslinks were also found formulation. Our findings rationalized terms varying degrees crosslinking opposite trend glassy at 20°C, where flexular belonged to explanation for those results offered free volume concept. FTi.r. analysis established clearly existence residual groups all formulations, even after post-cure. Etherification reaction hydroxyl takes place post-cure, but complete conversion cannot be attained owing topological constraints within three-dimensional network later stages This finding is particular significance mechanistic kinetic models absolute concentration