Surface characteristics of Pine and Heat-treated Spruce Modified with Alkoxysilanes by Sol-gel process

The surface morphologies and moisture behaviour of pine (Pinus sylvestris) sapwood and heat-treated spruce (Picea abies) deposited with two types of silane-based sol-gel coatings were studied by Atomic Force Microscopy (AFM), water contact angle and water uptake measurements. The distributions of sol-gel coatings on wood surfaces were investigated by Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). The two sol-gel coatings differed in terms of organic aliphatic chain length. The AFM results revealed that the sol-gel coatings applied by spreading covered the fine structure of the wood substrates. Thus, the sol-gel coatings - especially the one with short aliphatic chains - had a tendency to smoothen the wood surfaces. It was observed from the ToF-SIMS images showing Si ion distribution on treated surfaces that the coatings fully covered pine sapwood surfaces. The thin coating layers formed on heat-treated spruce surfaces followed the original wood surface structure. The contact angle measurements indicated that the water repellent properties of both pine and heat-treated spruce were improved to certain extent by the sol-gel coatings. However, the water absorption tests showed that water uptake was significantly diminished for sol-gel coated pine wood, whereas the relative low water absorption values of heat-treated spruce were affected by the sol-gel coatings.