The effect of short-chain cationic polymers on the deposition of wood resin emulsion droplets on silica surfaces

The objective of this work was to understand the mechanisms involved in the deposition of dispersed wood resin on solid surfaces. A hydrophilic silica surface, and a silica surface coated with adsorbed cationic polymer was exposed to an aqueous dispersion of wood resin. Deposition of wood resin as well as adsorption of cationic polymer were monitored by reflectometry in stagnation point flow. The deposition efficiency as well as the final deposited amount at pH 4.5 and 6.5 were measured as a function of NaCl and CaCl2, concentration. Droplets _of wood resin do not deposit on hydrophilic silica surface even from solutions of high ionic strength. If the silica surface is covered with a layer of cationic polyelectrolyte, droplets from an electrostatically stabilised dispersion deposit on the collector surface. In this case the deposition efficiency roughly agrees with barrier-less deposition. When the ionic strength is increased to render the dispersion somewhat unstable, the rate of deposition decreases. No deposition occurs if the dispersion is rendered completely unstable by addition of electrolyte. The dependence of the final deposited amount on ionic strength and added polyelectrolyte can be understood on the basis of the electrokinetic properties of the resin droplets. (C) 1999 Elsevier Science B.V. All rights reserved.