The implementation of the Biocide Products Directive and the impact of public opinion are the main reasons for dramatic changes in the field of wood preservatives. The new generation preservatives replace traditional protection agents on the basis of heavy metals, which have been approbated in a long-term practical experience. In parallel with searches for novel biocides, the modification of wood develops dramatically, and wood with improved bio-stability and physical properties enters for the market. However, there
is comparatively scarce information about the stability of the properties of these products in wood service conditions. There are also different viewpoints in respect to the protection mechanisms of modified wood against the action of rot fungi.
Studies of the microstructure and hydrophilic properties of thermally and chemically modified wood of different species by the water vapour method were carried out. Sorption-desorption isotherms were taken in three cycles, and their analysis was made by the comparative method in combination with the BET method. The obtained results indicate that the decrease in the hydrophility of wood upon thermal treatment in the temperature range 180-220oC makes up 45-54% (depending on the medium and temperature) and is connected mainly with the decrease of the accessible surface. The exposure of thermally treated samples in saturated water vapours results in the stabilization of their structure. After saturating with water vapours, the hydrophobizing effect decreases dramatically (to 15-32%), but still retains at a sufficiently good level. Acetylation as a method of chemical modification is most efficient from the viewpoint of hydrophobization: the microstructure of the modified samples is stable, the sorption cycles are repeatable. The hydrophobization effect for samples modified with furfuryl alcohol is lower than in the case of acetylation, and tends to decrease dramatically in moist medium. The results of the biological test testify that the reason for the bio- stability of acetylated wood is not the increased hydrophobicity, and another reason for it is to be found.
Keywords: Modified wood, Hydrophobicity, Bio-stability
Authors
V. Biziks
Latvian State Institute of Wood Chemistry, Riga, Latvia
B. Andersons
Latvian State Institute of Wood Chemistry, Riga, Latvia
J. Chirkova
Latvian State Institute of Wood Chemistry, Riga, Latvia
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