Abstract
The previous report dealt with the results of experiment on the wetting behaviors of non-treated fiber assemblies under various hydrostatic pressures. It was found that the water-resisting effects are dependent on the types of fibers, the porosity of the assemblies, and impressed hydrostatic pressures, and, furthermore, that the smaller the porosity of assembly, the lower the rate of downward flow of water, irrespective of types of fibers. The flow of water was completely impeded at a critical porosity.In the present paper the authors discuss the critical porosity of fiber assembly (PO-L) assuming the simplified model of the structure. This model assembly is assumed to have a structure in which the axis of fibers is so arranged in parallel and homogeneously that there exists inter-fiber capillary space of radius r. Then the water tension F on the wall of capillary space and hydrostatic pressure on the assemblies Wp, may be expressed as;where T and ρ are surface tension and density of water, h the height of water-column, θ contact angle, and g acceleration of gravity. The porosity of the assembly may be expressed as;where rf is radius of constituent fibers.In the case of 0°_??_θ_??_90°, balance of F and Wp is impossible and water does not permeate at r=0, so PO-L is 0%. In the case of 90°<θ_??_180°, if F+Wp=0 vix. r=-2 T/pgh•cosθ is held, water will not permeate and then the following relation is obtained.According to this relation, PO-L was calculated as function of contact angle and water pressure on nine samples of fiber assemblies and the results are tabulated. When any fiber assembly was finished by any water-proofing agent, the porosity at which the assembly becomes water-imperm eable can be approximately estimated from this Table, provided that the values of contact angle between the fiber and water are known. On the other hand, the contact angle will be obtained if the value of PO-L is known.
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