Hydrothermal modification for upgrading the durability properties of soft deciduous wood
B Andersons, I Andersone, V Biziks, I Irbe, J Chirkova, E Sansonetti, J Grinins, H Militz
To extend the application potentialities of soft deciduous wood, upgrading the durability properties, hydrothermal modification (HTM) of aspen alder and birch wood was investigated. The treatment was conducted in a multifunctional laboratory device WTT. In the previous cases it has been found that the treatment at 160oC improves the durability insufficiently. The modification at 180oC ensured a high resistance against white and brown rot fungi, but showed relatively great mass losses and a decrease in mechanical strength. In the further studies, a compromise between the improvement of durability and the decrease of mechanical strength will be looked for. HTM was carried out at the regimes 160oC/3 h and 170oC/1 h. Chemical composition, mechanical strength, microstructure, surface hydrophobility, durability against rot fungi, including after leaching, were determined for HT modified wood. It has been found that there are no essential differences among bending strength, hygroscopicity and surface contact angle at the regimes 160oC/3 h and 170oC/1 h for HT modified soft deciduous wood. The modified birch wood is the least durable against the test fungi, in comparison with aspen and alder wood. To ensure its durability, a higher modification temperature of at least 170oC is necessary, but to ensure mass losses below 3% - holding at 180oC is required. The durability of aspen wood against brown rot fungi can be reached with treatment at 170oC/1 h, but a temperature of 180oC is required for the protection against the white rot fungus. Modified alder wood is most durable against biodegradation. After leaching the modified aspen and birch wood, the durability against the action of P.placenta and C.versicolor increases. The fungi tests testify that, for the complex protection of aspen and birch wood (for reaching the durability class 1), HTM at 180oC is necessary but the wood modified under these conditions looses the strength dramatically. In its turn, to ensure the durability of alder wood, so high temperature is not required and the treatment at 170oC/1 h is enough.