Hybrid films synthesised from epoxidised castor oil, γ-glycidoxypropyltrimethoxysilane and tetraethoxysilane

Novel organic–inorganic hybrid films were synthesised through the reaction of epoxidised castor oil (ECO) with γ-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS). The amounts of GPTMS employed were sufficient to react with 25, 50 or 75% of the epoxy groups present in the ECO, whilst the mass proportions of ECO to TEOS varied from 90:10 to 70:30. Films were pre-cured at room temperature under an inert atmosphere, and subsequently submitted to thermal curing. Macro and microscopic properties of the films, including adhesion, hardness, swelling in toluene, microstructure (scanning electron microscopy) and thermal properties were determined as a function of the proportion of organic to inorganic precursor. Morphologic studies showed that the hybrid films were microscopically homogeneous when lower proportions of inorganic precursors were employed. Hardness and tensile strength increased, and swelling in toluene decreased, with the increase in the concentration of inorganic precursors. Good adhesion of the films to an aluminium surface was observed throughout the hybrid series.