Swelling and shrinkage of hard wood with water (Department of Forestry)

木材の膨潤乾縮に関する報告は多いが, 木材の主軸方向の膨潤乾縮に関する報告は比較的少ない。しかし, 主軸方向の膨潤乾縮も他の軸方向の膨潤乾縮と関連させて総合的に理解することが必要であろう。広葉樹散孔材5樹種について切線方向と主軸方向の膨潤乾縮量と含水率, 気乾比重, 要素の構成割合との関連性を検討した。両方向とも膨潤乾縮量と含水率とは非線形の関係を示し, 含水率8%以下の低い含水率領域でも膨潤乾縮量が認められた。しかし, 吸湿過程で収縮する含水率領域と脱湿過程で膨張する含水率領域がイスノキ, ヤブニッケイに認められた。切線方向の膨潤乾縮量は気乾比重, 放射組織, 柔組織との相関が認められたが, 主軸方向の膨潤乾縮量は比重, 構成割合ともに相関を示さなかった。要素の構成割合と膨潤乾縮量との相関が認められないことから, なんらかの他の因子が膨潤乾縮に影響しているものと推測される。膨潤乾縮は, 定性的には, 切線方向は主に比重に影響され, 主軸方向は切線方向の膨潤乾縮に間接的に影響されていると考えられる。The swelling of woods have been studied extensively, but there were few research reports about the longitudinal swelling of woods. It had to consider the longitudinal swelling in relation to the accompanying swelling of other axes of the wood. The longitudinal and tangential swelling of 5 diffuse porous woods was examined to relate moisture contents, specific gravity, and the element ratio of wood. Swelling in both axes was related to moisture contents with nonlinear relation and in the range of high moisture contents under fibre saturation point, the woods expanded with the increase of moisture contents. The woods of ISUNOKI and YABUNIKKEI swelled slightly in desorption process and shrunk in adsorption process. Tangential swelling was related to the specific gravity, the element ratio of ray and parenchyma cell. But longitudinal swelling was related to any factor. Some other factors, which were not examined in this study, should have an effect on longitudinal swelling. From these facts, it was considered that the tangential swelling was mainly effected by specific gravity and the longitudinal swelling was affected indirectly by the tangential swelling