Wood Modification in Latvia

This paper describes developments in research and process development in wood modification in Latvia. Several wood modification processes have been developed at the Latvia State Institute of Wood Chemistry. One of them was wood treatment with ammonia in the liquid or vapour phase with subsequent densification or bending and drying of the treated material. The second one was wood impregnation with resin solutions (phenol-formaldehyde condensates or silicones) with subsequent curing in the wood structure. The third one was impregnation of wood with monomers, or their mixtures, with subsequent polymerisation by gamma-irradiation or thermochemical methods. The monomers used were: styrene, styrene mixtures with acrylonitrile, vinylacetate, sulphur dioxide, oligoesteracrylates, acrylic acid, methylmethacrylate and acrylic or methacrylic acid. Decorative elements, flooring materials, insulating materials for electricity transfer lines; items for textile industry, gears, and some other items were produced from modified wood in experimental plant scale. Solid wood acetylation with acetic acid anhydride and other reagents were studied in Latvia University of Agriculture. Magnesium perchlorate catalyst, dichloromethane vapours, water and high frequency current were studied to increase the acetylation degree of wood. Laboratory trials resulted in designing, making up, and putting in action pilot equipment for solid wood acetylation with acetic anhydride in the liquid phase. Different trials with various reagents and solvents were performed to fix or to extract residual acetic acid from solid acetylated wood. Impregnation of wood with acetic anhydride is one of main process determinative factors. A mathematical model describing acetic anhydride diffusion in wood was created.