Waterborne Polymers for Water Repellent Wood Caotings

By Charles R. Hegedus, Frank R. Pepe, John J. Rabasco

Waterborne polymer, emulsions, composed of  vinyl acetate-ethylene (VAE), ethylene-vinyl chloride (EVCl), and other vinyl acetate copolymers were evaluated as polymer systems in water repellent coatings for exterior wood applications. Data presented indicates that these polymer emulsions exhibit an excellent balance of performance properties, making them the polymer of choice in water repellent coating formulations requiring low volatile organic compound (VOC) content.

The data further suggest that polymer morphology and other emulsion polymerization process parameters ( e.g., surfactant package, functional comonomers, initiation system, and particle size) may play a role in achieving industry accepted performance. There are over 30 million wood decks in the United States and the popularity of wood decking is growing due to its attractive features and its ability to add versatile living space.¹

These decks are exposed to a number of harsh exterior environmental conditions which can cause wood to degrade. Rain, sunlight, extreme temperatures, and temperature fluctuations cause wood to swell and shrink due to water absorption and release, as well as expand and contract from temperature fluctuations. These conditions induce high levels of stress and cyclic fatigue within the wood, causing the wood to develop checks, cracks, and raised grain, as well as degradation and discoloring of the wood surface.

Other deleterious factors causing wood to degrade include mildew growth, fungus, and insect attack. Because of these risks, lumber used to construct decks is usually pressure treated with a preservative, or the lumber used is a durable natural wood such as redwood or cedar.

Exotic hardwoods such as teak, tigerwood, ipe, and cumaru, which also tend to be durable, are becoming popular as well. A number of different compounds have been used as wood preservative treatments, but ammoniacal copper quat (ACQ), creosote solutions, and copper azole have been the most common.