Biologischer Angriff von acetyliertem Holz

Acetylation is an environmental friendly method to modify wood properties and protect it against biological attack. Many researches have been done in this field. However, no concern was paid for mode of protection in acetylated wood. This research had been aimed to study mode of action in acetylated wood by investigating on weight and MOE loss, chemical alteration in cell wall due to microbial attack, IRspectroscopy, microcalorimetry, determination of fungal biomass by using ergosterol assay and FDA hydrolysis and enzyme assays. Beech and Scots pine wood samples were acetylated by using acetic anhydride at temperature 80-120°C for 180min. Acetylated wood samples were tested under soil bed test condition, field and basidiomycete trials. Results showed that the losses of weight and MOE decreased at increasing weight gains. Soil bed test revealed that the acetylation of beech wood at above 8% and pine wood at above 10% inhibits soil microorganisms in attacking wood and their activities reached to nil at higher weight gains. A test with the white rot fungus (T. versicolor) showed that the weight loss decreased at raising weight gains. Weight gains of above 10% inhibited fungal decay in beech wood and it reached to zero at higher weight gains. Microscopical studies of wood from soil bed samples, field trials and basidiomycete (white- and brown-rot) tests showed that fungi could colonize acetylated and non-acetylated wood. However, measurements of fungal biomass by using ergosterol assays in those woods and fluorescein diacetate in white rottests showed a rapid colonization of fungal hyphae at early stages of incubation and decreased amount of fungal biomass at raising weight gains.Results showed that fungal colonization is influenced by the acetylation. Biological activities were measured in wood by using microcalorimetry. The reduction of thermal powers and measured amounts of energy production in acetylated wood revealed that activities of microorganisms were influenced by the acetylation and their activities decreased at increased degree of the acetylation. Microscopy of field trial samples showed that the acetylation of wood was affected the growth of soil microorganisms and protected wood against soil microorganisms during a long period of exposure (350 weeks) to soil.Different types of decay in field samples showed successional activities of soft- and white-rot fungi and also bacteria. Soil bed test showed a synergism between soil fungi and bacteria in wood. It was revealed that bacteria followed hyphal traces in cells and associated with fungi in wood degradation. Chemical analyses of acetylated wood in soil bed samples showed a significant effect of the acetylation on removal of cell wall components. The analyses showed a reduction in removal of cell wall components at increased weight gains. Results revealed that removal of the cell wall components reduced considerably in beech wood at weight gains above 8% and in Scots pine samples at above 10%. Study on patterns and phenol ogy of white- and brown-rot decay on acetylated wood showed no difference of decay patterns between acetylated and non-acetylated wood, however decay patterns appear more later in acetylated wood