Trial approach to the estimation of size distribution of free water paths in the undried heartwood of softwoods by a centrifugal method

Abstract

The size distribution of free water paths for six species of softwood was estimated from the amount of dehydrated free water under various centrifugal fields. The water permeability was evaluated simultaneously. The estimation was done by the centrifugal method, which is based on determining the balance of water potential decreased by centrifugal force and by the meniscus at small openings. The latter is determined by the radius of the capillary, the surface tension of the liquid, and the contact angle. The decrease in water potential produced by centrifugal force depends on the angular velocity, the distance from the rotational center to the dehydrated surface, and the distance inward from the dehydrated surface. We obtained the distribution of the effective radius of free water paths in undried heartwood from the distribution of the water saturation ratio in the centrifugal direction. The results showed that sugi, tsuga, and momi had peaks at around 0.50, 0.16, and 0.11 μm in the distribution curve of the free water path. The accumulation curve of the effective radius of free water paths successfully showed the water permeability. Sugi was the most permeable of the six species, and sitka spruce was the least permeable. Of the permeable species, earlywood had a larger radius than latewood.