Glycidoxypropyltrimethoxysilane modified colloidal silica coatings

Coatings were prepared from a suspension of colloidal silica particles containing glycidoxypropyltrimethoxysilane (GPS) and a polyamine curing agent. GPS was first added to an aqueous silica suspension which contained ethanol (30 wt%) to enhance mixing. The addition of GPS to a basic silica suspension favored condensation among the silane monomers and oligomers, resulting in precipitation. By contrast, acidic conditions resulted in slower condensation which allowed adsorption of the silane on silica, as followed by ATR-FTIR. After GPS addition and aging, the pH of the suspension was increased, a polyamine was added, and coatings were prepared on polyester web. Coatings with GPS modification were denser, adhered better to the polymer substrate, and could be made thicker than unmodified silica coatings.