Shrinkage and Swelling of Wood

The axial, radial and tangential shrinkages, which together account for the volumetric shrinkage, are directed by features of wood structure that resist shrinkage, e.g. the quantity of ray tissue in the radial direction, or by features of the 

The volumetric shrinkage to the oven-dry state is determined by measuring the green and oven-dry volume  

Volumetric shrinkage (%) = MC at fibre saturation (%) X basic density x 10 (2) 

Implicit is the fiuther assumption that the diameter and volume of the lumens do not change on drying. Optical microscopy confirms this to be a reasonable approximation (Beiser, 1933). Where there is a slight increase in the diameter of the lumen on drying the external volumetric shrinkage will be a little less than predicted, where the lumen decreases in size the external volumetric shrinkage will be somewhat more than predicted. Some variability is to be expected. 

In the same way, the volumetric swelling from the oven-dry state can be estimated using the following relationship  

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Boutelje J (1973) On the relationship between structure and the shrinkage and swelling of wood in Swedish pine (Pinus sylvestris) and spruce (Picea abies). Svensk Papperst., 76(2) 78-83... 

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