Manufacturing of Redispersible Powders

A redispersible powder is by definition a polymer in a powdered form that can be redispersed by adding water to it. The resulting emulsion will fulfill the functionality of a polymeric dispersion binder, normally within a cementitious or gypsum based system. Redispersible powders are manufactured by spray drying an emulsion (Fig. 13-1). 

Over 90 % of all industrial manufactured polymer dispersions are produced by emulsion polymerization. The most important monomers, which are being used for applications in the building/construction industry, are vinyl acetate, ethylene, versa-tic acid esters, vinyl chloride, styrene and acrylics. Especially the use of ethylene as a co-monomer offers some extraordinary advantages  

To guarantee the performance of a redispersible powder in its final application a protective colloid is added to the emulsion before the spraying process. The colloid protects the polymer particles from film forming during the spray drying process 

2 Manufacturingof Redispersible Powders 331 responsible for that the powder will redisperse in water again (Figs 13-2 

Over the years poly vinyl alcohol (abbreviated PVOH or PVAl) proofed to be the most preferred protective colloid for that purpose. In a cementitious environment PVOH will be partly saponified and also absorbed of fine particles within a mortar, i.e. cement and fillers. This results in a film forming of the dispersed polymer and finally the polymer film is not redispersible any more. Since the polymer film (acting as a binder) is distributed throughout the cement matrix it improves dramatically the adhesion, abrasion resistance, flexural strength, flexibility, water impermeability/water repellency (hydrophobicity) and workability of a cementitious system. 

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