Investigation of a waterborne epoxy for E-glass composites

We present a continuing investigation of epoxies based on diglycidyl ether of bisphenol A cured with 2-ethyl-4-methylimidazole in the presence of the nonionic surfactant Triton X-100. Interest in this epoxy system is due part ially to its potential application as a waterborne replacement for solvent- cast epoxies in E-glass-laminated printed circuit boards. The surfactant ad ditive could potentially alter the interfacial properties and durability of composite materials. Previous studies revealed that the viscoelastic behav ior of the cured epoxy is altered when it serves as the matrix in a glass-f iber-reinforced composite. The additional constraining and coupling of the E-glass fibers to the segmental motion of the epoxy matrix results in an ap parent increased level of viscoelastic cooperativity. Current research has determined that the cooperativity of an epoxy/E-glass composite is also sen sitive to the surface chemistry of the glass fibers. Model epoxy/E-glass co mposites were constructed in which the glass was pretreated with either 3-a minopropyltriethoxysilane or 3-glycidoxypropyltrimethoxysilane coupling age nts. Dynamic mechanical analysis was then used to create master curves of t he storage modulus in the frequency domain. The frequency response of the m aster curves and resulting cooperativity plots clearly varied with the surf ace pretreatment of the glass fibers. The surfactant had surprisingly littl e effect in the observed trends in the cooperativity of the composites. How ever, the changes in cooperativity due to the surface pretreatment of the g lass were lessened when the samples were prepared from waterborne emulsions . Moisture-uptake experiments were also performed on epoxy samples that wer e filled with spherical glass beads as well as multi-ply laminated composit es. No increases in the diffusion constant could be attributed to the surfa ctant. However, the surfactant did enhance the final equilibrium moisture-u ptake levels. These equilibrium moisture-uptake levels were also sensitive to the surface pretreatment of the E-glass. (C) 2000 John Wiley & Sons, Inc .