Use of high molecular-weight polyvinyl alcohol in vinyl acetate type of emulsions

 
The use of polyvinyl alcohol (PVOH) as protective colloid for the emulsion polymerization of vinyl acetate (VAc) or its usage as post additive in dispersions has been long known. PVOH with a lower degree of hydrolysis increases the polymerization stability and the formation of lower particle size whereas higher degree of hydrolysis PVOH improves the water resistance. The advantages conferred on the emulsion based adhesive by the presence of PVOH, such as suitable rheology, good adhesion to cellulose substrates, setting speed, and high cohesion of the polymer film are common knowledge. Also the hydrophilic nature of PVOH is well known to have detrimental impacts on the properties of the emulsion polymer films. In this study we will present the performance of high-molecular-weight PVOH as protective colloid for the emulsion polymerization of vinyl acetate dispersions. The paper will clearly show that a high viscosity emulsion can be prepared using a low dosage of this novel high-molecular-weight PVOH. The impact of post addition of this high molecular PVOH on VAc type emulsions will also be presented. The addition of this novel high molecular PVOH increase significantly the thixotropic behavior compared to standard PVOH. Additionally, in view of the good compatibility of this novel PVOH with VAc type emulsion, it increases significantly the storage stability of the emulsions. This novel PVOH may be used as rheological modifier instead of classical rheology additives that may not have a good compatibility with VAc type of emulsions.