Epoxy resin modified with in situ generated metal oxides by means of sol–gel process

Organic–inorganic hybrids were prepared with silica, zirconia, or titania in situ generated within epoxy resins based on bisphenol A diglycidyl ether and Jeffamine® by means of the aqueous sol–gel process. The morphology of the prepared hybrids varied from a particulate dispersed phase to a co-continuous morphology. Silica and zirconia filled epoxies were characterized by a significant increase in thermal stability, attributable to the high thermal stability of silica and zirconia phases. On the contrary, the introduction of titania induced a strong decrease in thermal stability of the epoxy/titania hybrids compared with the pure epoxy resin, attributable to metal-catalyzed oxidative decomposition mechanism in the polymer/titania composite. Hybrids were much more transparent than unfilled epoxy. The transmittance of silica- and titania-based hybrids showed a slight decrease by increasing the content of filler, while the transparency of zirconia-based hybrids was very high and almost constant independently by the nominal content of filler. The presence of in situ generated fillers significantly enhanced the scratch resistance of the epoxy resin as indicated by the marked increase of critical load for all the hybrids.