Evaluation of capillary radii in wood by the centrifugal method.

1.离心法是利用离心力降低的水势和毛细压力与离心力脱水的游离水量的平衡来估算6种软木自由水径大小分布的一种新方法。其分布取决于树种和在树林中的位置。例如，早期坞的半径大于晚期坞的半径。这一结果被认为是未干燥木材的特征，因为干燥样品的结果与此相反。用离心法定量地得到了局部蒸汽爆炸时自由水路有效半径的变化。由于凹坑边缘与凹坑环面的粘附强度大，凹坑在边材中比在心材中更容易受到离心力的破坏。杉木比红杉更容易发生坑损，这是由于杉木的环面直径与坑孔直径之比大于杉木，杉木的环面支撑强度大于杉木。杉木边材破坏凹坑所需的力为0.1 ~ 0.2 MPa。对于心材的凹坑，用离心法估计出较大的值。这意味着木材中的凹坑有可能在干燥过程中被毛细张力破坏。在潮湿条件下，木材的接触角一直被认为为零。然而，这不是事实。心材的润湿性较边材差，但经吸湿热处理后，两者的接触角相同。这一趋势与醇苯萃取处理相同。这意味着即使在潮湿的条件下，细胞壁上提取物的存在也会影响细胞壁的润湿性。

1.The size distribution of free water paths for six species of softwood was estimated by centrifugal method which is a new method developed from the balance of water potential decreased by centrifugal force and capillary pressure by meniscus and the amount of dehydrated free water by centrifugal force. The distribution depends on species and the location in wood. For example, the radius in earlywood was larger than one in latewood. This result was presumed to be the feature for undried wood as there was the contrary result for dried sample.2.The change of effective radius of free water paths by local steam explosion was obtained quantitatively by the centrifugal method.3.The damage of pits by the centrifugal force was easier in sapwood than in heartwood because of the strength of adhesion between pit border and torus. Pits in Sugi damaged easier than those indouglas fir because the ratio of the diameters of torus and pit aperture is larger in douglas fir than in sugi and the torus in douglas fir was supported stronger than one in sugi.4.The force required for the damage of pits was 0.1 to 0.2 MPa for the sapwood in sugi. For the pits in heartwood larger value was estimated by centrifugal method. This means pits in wood has possibility to be damaged by capillary tension during drying.5.The contact angle of wood was considered to be zero in wet condition so far. However it was not truth. Wettability in heartwood was poor than sapwood, but after hygroscopic thermal treatment both location showed same contact angle. This tendency was same to the alcoholbenzene extractive treatment. This mean that the existence of the extracives on cell wall affects to the wettability even the wet condition.