Decay resistance of ammonia-plasticised and densified beech wood

Degradation by wood-rotting fungi has been studied in Lignamon and beech wood modified by the Lignamon process. Different treatments that are used during Lignamon process were applied: gaseous ammonia treatment, densification (20 and 40% compression ratio) and heat treatment (180°C). These specimens were exposed to Trametes versicolor and Coniophora puteana for 16 weeks and the mass loss was evaluated. Changes in chemical structure, nitrogen content and pH caused by individual treatments or by fungal activity were also determined. The wood nitrogen content increased after ammonia treatment (1.0%) and was the highest in Lignamon (1.4%), its release during water leaching was very slow. The chemical analysis of wood revealed slight changes in the polysaccharide and lignin content in wood treated with ammonia. Bonded nitrogen was in the form of amides, which were partially thermally degraded by heat treatment. Neither densification nor heat treatment led to better resistance of wood against fungi, while ammonia treatment significantly restricted mass losses (C. puteana 2.5%; T. versicolor 7.5%) compared to untreated wood (both about 30%). Lignamon showed the best fungi resistance (mass loss < 5%), which was probably caused by the combined effect of hemicellulose degradation, an increased nitrogen content, and wood densification.