In the near future, the wood from silver birch (Betula pendula Roth) plantations will broadly increase as a source of raw material of saw and veneer logs. Due to the differences in growth rate and silviculture, the raw material from plantations is likely to have characteristics different from those of the wood harvested from naturally regenerated forests. In the further processing of sawn birch timber, the drying of wood is one of the most difficult phases: discolouration, deformation, moisture content gradient, being typical defects for dried birch timber.
The objective of this thesis was to study the drying behaviour and related wood and timber properties of plantation-grown silver birch. The wood procurement season and storage of logs were studied as a source of variation of wood properties and drying behaviour. To study the variation in wood properties and drying behaviour caused by the drying method, the conventional kiln drying (heat and vent drying) and vacuum drying were used. On the subject of drying method, wood colour, shrinkage, weight density, final moisture content, Brinell hardness and equilibrium moisture content were studied. The role of proanthocyanidins and their polymerisation as a chemical background for the discolouration was studied.
The drying behaviour, the initial moisture content of the wood, basic density and proanthocyanidin content were found to change with the wood procurement season. These changes were consequences of the physiological alterations in birch trees with the seasons and they were found to have an influence on colour, density, equilibrium moisture content and Brinell hardness of wood. Regarding the conventionally dried wood, the discolouration was the most intensive for summer-felled wood while the vacuum-dried wood discoloured the most intensively when it was felled in winter. In summer-felled and winter-felled wood the storage of timber as logs increased the discolouration of the wood during drying.