Effect of stoichiometry and cure prescription on fluid ingress in epoxy networks



Stoichiometry and cure temperature were evaluated for epoxy systems based on the diglycidyl ethers of bisphenol-A and bisphenol-F and cured with 3,3′- or 4,4′-diaminodiphenylsulfone. The materials were formulated as stoichiometric benchmarks and with an excess of epoxide and cured in two steps (125°C/200°C) or one step (180°C). Dynamic mechanical analysis and free volume testing indicated decreased crosslink density and increased chain packing in the excess-epoxy materials, as well as a narrowing gap in properties between 33- and 44-cured networks with excess epoxy. The narrowing gap was less pronounced in materials cured at 180°C. The excess-epoxy materials were more resistant to water ingress, exhibiting reduced equilibrium water uptake. The excess-epoxy materials were also more resistant to methyl ethyl ketone ingress, which occurred at a slower rate in most excess-epoxy materials. The improvement in fluid resistance was attributed to enhanced chain packing in the materials with lower crosslink densities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013