In the moderate climatic zone, in which also Latvia is located, mainly coniferous wood is used in construction, whose properties are more appropriate for load-carrying and bearing structures. The stock of the main deciduous tree species (birch, grey alder, aspen and black alder) in Latvia’s forests is about 229.2 million m3. From soft deciduous wood (grey alder, aspen), mainly small-size assortment is currently produced, for example, box boards, pallets, bath-house facing boards. To extend the applicability potentialities of deciduous wood by improving its biological durability and hydrophobicity, thermal treatment was investigated.
In the present study, birch (Betula spp.), aspen (Populus tremula) and grey alder (Alnus incana) wood samples were used. The task was to elucidate the effect of the hydrothermal treatment process on the biological durability and mechanical properties of wood, and to find optimal treatment parameters so that to compromise between the improved biological durability and the declined mechanical strength. Modification was carried out in a multi-functional pilot device WTT in elevated water vapour pressure conditions at five different treatments (temperature, ˚C/duration, h): 140/1; 160/1; 160/3; 170/1 and 180/1.
The modification at 140˚C does not improve the durability of the modified soft deciduous wood against rot test fungi, white rot (Coriolus versicolor) and brown rot (Coniophora puteana); mass losses are similar and even greater than those for the control wood, which could be explained by the presence of easily usable thermal degradation products. The treatment temperature 160˚C improves the durability against brown rot fungi (mass losses decrease by 30-40%), to a lesser extent- against white rot fungi (mass losses decrease by 6 -15%). Protection against fungi is reached, when modifying wood at 180˚C.
Modification for 1 h at 140˚C and 160˚C increases the bending strength of birch wood by 31-34% and 8-10%, respectively, in comparison with the bending strength of untreated wood. Extending the treatment time up to 3 at 160˚C, bending strength decreases dramatically (by 26-28%) and is similar to that for wood modified at 170oC/1 h. Thermal modification for 1 h at 180oC decreases the bending strength by 50-55% and is not suitable for producing high-quality material.
Keywords: hydrothermal treatment, grey alder, aspen, birch, mechanical and biological durability
Authors
Biziks V.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Andersons B.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Andersone I.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Irbe I.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Login to download the PDF