Phase structure and mechanical and adhesion properties of epoxy/silica hybrids

Organic/inorganic hybrids containing 4– to 19.8 wt% of silica were synthesized from an epoxy resin diglycidyl ether of bisphenol-A (DGEBA) and a γ-glycidoxypropyltrimethoxysilane (GPTMS) or a tetramethylorthosilicate (TMOS) by utilizing a sol/gel process. In the DGEBA/GPTMS hybrids, the storage modulus in the rubbery region increased and the peak area of the tan δ curves in the glass transition region decreased, respectively, with the hybrization of small amounts of silica. This may result from the suppression of the epoxy network moiety with the incorporation of the silica network. Observation using transmission electron microscopy (TEM) revealed that the silica networks are uniformity dispersed in the hybrids. Furthermore, the hybrids with GPTMS showed a very high adhesion strength for the silicone rubber. Results from the X-ray microanalysis show that the silica networks are concentrated in the interfacial area of the adhesive joints with silicone rubber. In the swelling test of silicone rubber with the epoxy resin containing GPTMS, the degree of swelling increased with increasing GPTMS content. The high adhesion strength observed in the DGEBA/GPTMS hybrids was caused by the immersion of the adhesives into the surface layer of the silicone rubber substrate, which was attributed to the good affinity between GPTMS and the silicone rubber.