Determination of Dynamic Shrinkage in Beech and Spruce Wood During Drying Using X-ray Spectroscopy

The dynamic of shrinkage in beech (Fagus sylvatica) and spruce (Picea abies) was non-destructively determined during drying using X-ray spectroscopy. Furthermore، electron microscopy (ESEM) studies were carried out and the pattern of moisture gradient evolution was determined in order to precisely characterize the dynamic of shrinkage. The results showed that the dynamic of shrinkage is different for beech and spruce. The shrinkage of beech wood occurred during the bulk (capillary) flow of free water when the surface moisture reduced below fiber saturation point. In contrast، the shrinkage of spruce wood only occurred at the domain of bound water diffusion. The uneven pattern of shrinkage in beech wood reveals that the shrinkage of beech is more anisotropic than that of spruce. In the case of both woods، especially in beech، in spite of moisture reduction at the domain of bound water diffusion close to the final moisture، shrinkage did not occurred. Since the beech wood cells didn’t suffer from collapse، it can be concluded that the considerable shrinkage of beech wood at the domain of free water can not be due to the cell collapse at a result of capillary tension.