EFFECT OF SILANATION OF FILLERS ON THEIR DISPERSABILITY BY MONOMER SYSTEMS

The effect of silanation on the dispersion of quartz and zirconia-sili ca fillers by monomers used to formulate composites was studied. Sixte en silane coupling agents and three methods were used, and the amounts of the monomers needed to reach wet and flow point values were determ ined. The silanes were selected to have a variety of organofunctional and hydrolysable groups. Silanation was done from an ethanol-water sol ution of the silanes and by adding the silanes directly to the filler at room temperature (24 degrees C) and at the boiling temperature of t he silanes. The amount of silane used was either that required to prod uce minimum uniform coverage on the fillers or three times the minimum coverage. All silanes and all methods of treatment decreased the flow values for both fillers compared to the unsilanated controls. General izations were that the effectiveness of silanation on the dispersion o f the filler particles was greater (i) when silanation from ethanol so lution was used compared to direct addition; (ii) when three times the minimum uniform coverage was used; (iii) when the silane contained me thoxy rather than ethoxy groups; (iv) when the silanes were trialkoxy rather than dialkoxy compounds; (v) when the length and bulkiness of t he organic functional group was smaller; and (vi) when the organic fun ctional group was methacrylate rather than acrylic. The strength of co mposites prepared from one of the monomer systems and quartz silanated with methacryloxypropyltrimethoxysilane was higher than those silanat ed with acryloxypropyltrimethoxysilane, which supports the use of the wet and flow point values as screening tests for estimating the disper sability of fillers.