Influence of anti-caking agent kaolin on film formation of ethylene–vinylacetate and carboxylated styrene–butadiene latex polymers

Colloidal stabilizers (e.g. PVOH) and anti-caking aids (e.g. kaolin) are commonly added during the spray drying of liquid latex dispersions to produce re-dispersible polymer powders for the drymix mortar industry. Here, the influence of kaolin and polyvinylalcohol on polymer film formation of an ethylene–vinylacetate (EVA) and a carboxylated styrene–butadiene (SB) latex dispersion in water and cement pore solution was investigated. Time-dependent ESEM analysis was conducted to analyze the progress of particle coalescence. The results show that both EVA and SB powders form a homogeneous film much faster than their liquid precursors. Surprisingly, this effect was found to result from the presence of kaolin. Consequently, this additive fulfills a dual purpose in re-dispersible powders, it serves as anti-caking agent and also accelerates film formation while polyvinylalcohol retards particle coalescence. The SB latex achieves a coherent polymer film faster than the EVA dispersion, due to its smaller particle size (~ 200 nm).