Hansmann Christian, Konnerth Johannes, Rosner Sabine
Wood K plus-Competence Centre for Wood Composites and Wood Chemistry, St. Peter Str. 25, AT-4021 Linz, Austria.
Wood Mater Sci Eng. 2011 Mar 21;6(1-2):2-6. doi: 10.1080/17480272.2010.515032.
Contact-free digital image analysis was performed of the radial shrinkage of fresh, fully saturated small spruce wood beams. An experimental test set-up was developed to ensure constant distance from the charge-coupled device camera to the sample surface as well as constant climate and light conditions during the whole experiment. Dimensional changes were observed immediately after the drying process began. An unexpected distinct effect could be observed which could not be explained by drying surface layers only. After a fast initial radial shrinkage a slowing down of the dimensional changes occurred at high mean moisture contents. A complete interruption of any dimensional changes followed. Finally, a recovery from shrinkage was even observed. It is assumed that strong negative pressure occurred in the fully saturated capillaries owing to dehydration which led to additional dimensional changes. As a consequence, the break of the water column and aeration in these capillaries finally resulted in a recovery period in the shrinkage rate due to the pressure release. After this effect, the dehydration was characterized by a phase of fast and almost linear shrinkage due to drying surface layers. Finally, the shrinkage slowed down to zero when reaching equilibrium moisture content.
对新鲜、完全饱和的小云杉木梁的径向收缩进行了非接触式数字图像分析。开发了一个实验测试装置，以确保在整个实验过程中电荷耦合器件相机到样品表面的距离恒定，以及气候和光照条件恒定。在干燥过程开始后立即观察到尺寸变化。可以观察到一种意想不到的明显效果，这不能仅用干燥表层来解释。在快速的初始径向收缩之后，在高平均含水量时尺寸变化减缓。随后尺寸变化完全中断。最后，甚至观察到收缩的恢复。据推测，由于脱水，在完全饱和的毛细管中产生了强大的负压，这导致了额外的尺寸变化。因此，这些毛细管中的水柱断裂和通气最终由于压力释放而导致收缩率的恢复期。在这种效应之后，脱水的特征是由于干燥表层而快速且几乎呈线性收缩的阶段。最后，当达到平衡含水量时，收缩减缓至零。
