PERFORMANCE CHARACTERISTICS OF COATINGS ON BASIS OF POLYVINYL ACETATE MODIFIED WITH MONTMORILLONITE

Abstract

Water-dispersion materials based on poly (vinyl acetate) are widely used in industry as adhesive compositions and binders for polymer coatings due to their low cost, ecological safety and good performance characteristis. Drawbacks of such materials are insufficient water resistance and relatively low physical-mechanical properties. For improvement of performance characteristics of poly (vinyl acetate) based coatings it is proposed to modify the water-dispersion materials by incorporation of small amounts of sodium montmorillonite. In the article characteristics of model pigmented paint materials and coatings based on poly (vinyl acetate) dispersion modified with sodium montmorillonite are presented. Commercial water dispersion of PVA plasticized with dibutyl phatalate, natural sodium montmorillonite and titanium dioxide (pigment) were used for preparation of model paint materials. The obtained specimens of model paint materials are pseudoplastic fluids, incorporation of monmtorillonite leads to significant increase in yield stress. Materials modified with montmorillonite exhibit thixotropic properties. Addition of 1-2 % wt. montmorillonite to the material leads to increase in the Young modulus of dried films up to 8 times without decrease in tensile strength. The obtained effect is attributed to adhesion strengthening of the composite material. Incorporation of montmorillonite does not hinder the covering power of the paint material. Montmorillonite-modified coatings show increased hardness and reduced water absorption capacity (up to 2.5 times with addition of 2 % wt. montmorillonite). Reduction of water uptake of polymer material modified with montmorillonite can be attributed to reduction of free volume in the composite, formation of interface layers of polymer with different physico-phemical properties, and also to the decrease in the diffusion coefficient of water in the composite. The suggested approach to inprovement of the coating characteristics can be implemented without major expenditure due to low cost of natural sodium montmorillonite and simplicity of its incorporation in water-dispersion materials.