Silica-Filled Composites from Epoxidized Natural Oils

Thermosetting cast resins, filled with varying levels of silica, were prepared from epoxidized soybean oil (ESO) and epoxidized triolein (ETO) in order to study matrix-filler interactions and effects of cross-linking density on physical properties. While ESO is characterized by a highly heterogeneous composition, ETO had very regular structure but lower epoxy content. Room temperature ring opening polymerization initiated with butanediol was catalyzed by fluoroboric acid. Epoxy matrices were almost entirely made from natural oils, with cross-link densities correlated with epoxy oxygen content in the epoxidized oils. In spite of high cross-link density, glass transitions of ESO and ETO matrices were below room temperature, which was attributed partially to the plasticizing effect of dangling chains and side reactions (cyclization). Ground silica particles increased strength and modulus but did not shift glass transition in a predictable way. The impact of filler on mechanical properties was more pronounced in composites prepared with lower functionality ETO. These rapidly setting materials were prepared by a simple process of mixing and casting. The resulting inexpensive epoxy composites displayed relatively low polarity and low dielectric loss, particularly in the glassy state, and therefore may show utility in electrical insulation applications.