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 ex posed to an aqueous dispersion of wood resin. Deposition of wood resin as w ell as adsorption of cationic polymer were monitored by reflectometry in st agnation point flow. The deposition efficiency as well as the final deposit ed 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 elect rostatically stabilised dispersion deposit on the collector surface. In thi s case the deposition efficiency roughly agrees with barrier-less depositio n. When the ionic strength is increased to render the dispersion somewhat u nstable, the rate of deposition decreases. No deposition occurs if the disp ersion is rendered completely unstable by addition of electrolyte. The depe ndence of the final deposited amount on ionic strength and added polyelectr olyte can be understood on the basis of the electrokinetic properties of th e resin droplets. (C) 1999 Elsevier Science B.V. All rights reserved.