Simultaneous drying and densification of silver birch (Betula pendula L.) veneers: analysis of morphology, thickness swelling, and density profile

摘要

In this study, birch {Betula pendula L.) veneers were simultaneously densified and dried using a contact drying method at pressures of 1.5 and 3 MPa at 130 ℃and compared with veneer dried in a laboratory-scale con-vective type dryer. Compression rate, thickness swelling, and the density profiles of the veneers were investigated. Furthermore, the microstructure of densified veneers was studied by scanning electron microscopy (SEM). A maximum veneer compression rate of 9 % was achieved at a pressure of 3 MPa. Under these conditions, the veneers were, on average, densified from 504 to 574 kg m~(-3) (approximately 14 %). After water soaking, full set-recovery-recovery to the initial thickness-occurred. However, the swelling rate was lower for the densified veneer. Density profiles measurements showed that densification occurs throughout the veneers. The SEM images showed that the surface of the densified veneers were smoother, whilst no cracks were detected due to densification. Densification seemed to occur in vessels. Typically, rays were bent when there was a vessel nearby.