Deformation pattern of compressed wood cell walls in radial direction and its effect on modulus of rupture values in different loading directions.

This study aimed to determine the deformation pattern of compressed wood cell walls and the effect of loading directions on modulus of rupture (MOR) values of radially compressed wood in drying set condition. Hinoki (Chamaecyparis obtusa End1.) wood with a specific gravity of0.44 was used to determine the deformation pattern because it has a clear boundary between early and latewood. The deformation levels were observed at strain levels of 0.1, 0.2, and 0.3. Microscopic observations of wood cell walls were carried out using a Laser Scanning Microscope (LSM) at a scale of 200 µm. The wood samples used for bending tests were Agathis (Agathis sp.) and Rubber wood (Hevea brasiliensis) with specific gravity of 0.45 and 0.70, respectively. The wood samples were compressed in the radial direction at 0.35 strain level or 35%, after softening by using a hot press at 100°C for 4 hours until it reached drying set condition without being damaged. The results showed that the deformation of wood cell walls at a strain level of 0.1 started from the surface and the earlywood, which has thin cell walls. At strain levels of 0.2 and 0.3, the number of deformed cell walls at the surface and below the latewood increased, and only the latewood cell walls remained unchanged. MOR values of uncompressed wood in radial loading direction were almost the same as that in tangential loading direction. However, the MOR values of radially compressed wood in the tangential loading directions were higher than those in the radial loading directions. Compression in the radial direction collapsed the wood cell walls from their initial shapes to almost flats and arranged the structure tangentially. Therefore, the MOR values of radially compressed wood increased when it was loaded parallel to its tangential direction. [ABSTRACT FROM AUTHOR]