Abstract
The influence of shear, electrolytes, polyelectrolytes (anionic trash), and surfactants on the colloidal stability of differently formulated AKD dispersions was investigated. The stability was tested under shear in a Britt Dynamic Drainage Jar by measuring particle size distributions and microelectrophoretic mobilities. Three cationic dispersions were used, stabilised with (1) starch with low charge density, (2) starch with medium charge density and a polyaluminum salt, (3) synthetic polymer with high charge density.
All dispersions showed good to excellent stability to high levels of shear and electrolytes.
All tested dispersions were influenced by carboxymethylcellulose, CMC, and flocculation was induced at a CMC addition giving a z-potential around zero. Dispersions with a higher charge density formed larger flocs and the floc size was a function of the ratio dispersion/CMC. The presence of xylan and sodium oleate only affected the dispersions with high charge density.
Experimental results and theoretical calculations of the rate of AKD flocculation are in good agreement. The theoretical calculations are based on Smoluchowski’s equation for collisions between spherical particles in a uniform shear with a correction for hydrodynamic and van der Waals forces between the particles. Calculations indicate that AKD flocculation can compete with deposition on fines and fibres under papermaking conditions.
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