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Wednesday, 21 August 2019
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Raw materials & technologies, Raw materials, Coatings fillers

Kaolin accelerates film formation of latex polymers in cement

Friday, 14 February 2014

Colloidal stabilisers (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.

Scientists found that kaolin can accelerate film formation of latex polymers in cement

Source: Stefan Körber - Fotolia.com

Scientists found that kaolin can accelerate film formation of latex polymers in cement

Source: Stefan Körber - Fotolia.com

In their study, two researchers from Technische Universität München (TUM), Germany, investigated 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. They conducted time-dependent ESEM analysis to analyse the progress of particle coalescence.

Polyvinylalcohol retards 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 (~200nm).

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