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National and European legal rules and regulations require the replacement of solvent paints by water-born paints. Water on wood surfaces leads to significant problems because water can penetrate the pore system of wood and causes a swelling of the wood. The aim of our work was the reduction of water uptake of wood by polyelectrolytes with the surface polarity and wetting behavior of the wood surfaces should not be significantly changed. Cellulose materials, such as wood show in presence of moderately acidic, neutral or basic aqueous solutions a negative net surface charge. Therefore, for surface modifications of wood samples different commercially available cationic polyelectrolytes were used. In particular, weak polyelectrolytes were likely to reduce the water uptake of wood. They also slightly decrease the surface polarity of wood surfaces, which was advantageous for the rapid wetting of wood. Moreover, the reactive functional groups of the weak polyelectrolytes were used for subsequent cross-linking reactions to form irreversibly anchored polyelectrolyte networks on the wood surfaces.

Summary: Nano-sized zinc oxide (ZnO) was chosen as a suitable candidate for the UV-protection of coatings. ZnO-based acrylate coatings were applied to polycarbonate plates, glass plates and impregnated wood. Coated samples were artificially weathered (Xenon test) for at least 1500hours and studied with regards to their optical and mechanical properties, such as color shifts (yellowing), as well as to changes in brightness, transparency or hydrophobicity. The prepared wood coatings showed reduced yellowing and improved optical properties.

Nanocomposite UV coatings with adjustable properties for use on wood substrates in outdoor conditions were developed. Nanoscale ZnO was shown to be an efficient light absorber. Coatings were characterized in terms of elongation at brake, residual PI and double bond conversion, universal hardness, transparency, hydrophobicity, and yellowing. Coated samples were artificially weathered and studied with regard to their optical and mechanical properties, as well as to changes in brightness, transparency, hydrophobicity, and water permeability. The prepared wood coatings showed an increased weather fastness and improved optical properties. The suitability for use in outdoor conditions was assured by optimizing the elasticity of the coating and decreasing its water permeability.