Waterborne silane systems

Chem. Descrip. Waterborne silane with amine functionality Uses Coupling agent in mineral surface treatment, acrylic coatings and caulks, antifreeze systems, and metal primers Properties Completely sol. in water dens. 1.1 g/ml vise. 4-6 mFa-s- f.p. 

In most cases the silane is applied to the filler neat or in diluted form. Typically the silane or silane solution is sprayed onto the filler as it is being agitated. Most important commercial silane coating processes are continuous, with high throughput rates, but application may also be performed in batches. Control of silane addition, dwell time, and temperature within the system is essential for a suceessful coating. Evolution of volatiles (VOC) must be monitored. To remove reaction byproducts, solvents, and water, and to bond the silane to the filler surface, further heat treatment may be necessary. For those fillers typically processed as a slurry, aqueous treatment with waterborne silanes is also possible. 

Two different approaches have been taken toward waterborne alkoxysiloxane and alkoxysilane waterproofing materials. The recent patent literature contains many references to emulsions of alkoxysilanes and silane—resin mixtures (87) that claim stabihty to hydrolysis until the emulsions are applied and allowed to dry on the masonry, at which point hydrolysis and condensation are underway. Alkoxysilane stabihty within the emulsion is obtained through judicious choice of emulsifiers and the use of buffering agents to minimize pH drift. Excellent performance in static water holdout tests may be obtained with these systems, although initial water beading by the cured coatings can be somewhat compromised by the presence of surfactant. 

Silanes can be polymerized into the backbone of a polymer during its synthesis [6]. Emulsion polymerization of methacryloxyalkyl or vinyl functional organosilanes has been shown to be a particularly useful method of incorporating a crosslinking silane into a waterborne system. Subsequent to reaction of the methacryl or vinyl functionality, the alkoxy groups are left available either to react with a substrate or filler, or to crosslink upon film formation. 

These methods offer an opportunity to measure the phenomena that cause instability of silane-containing formulations, and are valuable to the continued understanding of the complex factors that should be considered when formulating with silanes in real-world waterborne systems. 

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