The wicking of liquid into a paper-like swelling porous medium made from cellulose and superabsorbent fibers was modeled using Darcy's law. The work is built on a previous study in which the Washburn equation, modified to account for swelling, was used to predict wicking in a composite of cellulose and superabsorbent fibers. In a new wicking model proposed here, Darcy's law for flow in porous media is coupled with the mass conservation equation containing an added sink or source term to account for matrix swelling and liquid absorption. The wicking-rate predicted by the new model compares well with the previous experimental data, as well as the modified Washburn equation predictions. The effectiveness of various permeability models used with the new wicking model is also investigated.

in Wiley InterScience (www.interscience.wiley.com).Wicking of liquids in polymer wicks made of sintered polymer beads is studied experimentally where three different polymer wicks (made from polycarbonate, polyethylene, and polypropylene) and three different well-characterized liquids (hexadecane, decane, and dodecane) are used to plot the mass of wicked liquid as a function of time. The experimental results are compared with the predictions from the Washburn equation as well as a Darcy's law-based formulation. The suction pressure needed to pull the liquid up a wick in the formulation is modeled using a new energy balance (EB) method and a capillary method. In the former, the released surface energy during wetting is equated to the viscous losses during liquid motion; in the latter, the suction pressure is obtained by treating the wick pore-space as a bundle of capillary tubes. The Darcy's law-based formulation also considers the effect of gravity in its predictions. The newly proposed EB method in conjunction with gravity yields the most satisfying predictions. All parameters used in the proposed model were measured independently and no fitting parameters were used. The success of this method is especially notable for a large-pore polypropylene wick where it was the only model to predict the final steady-state height for the liquid column.

Woven jute fibers, a class of affordable and biodegradable ‘green’ fibers, are being increasingly used as a substitute for the artificial glass and carbon fibers used in polymer composites. However, all natural fiber composites absorb water and swell in a moist environment For the first time, the swelling and weight gain behavior of bio-based composites made from jute fibers and bio-based or ordinary epoxy is presented in this experimental characterization study. Several such composites specimens were made using a low-pressure resin injection process similar to resin transfer molding; the specimens were made according to ASTM D 570 consisted of three compositions: pure resin, pure resin with a single jute fabric layer, and pure resin with two jute fabric layers. The effects of number of layers on moisture absorption, thickness swelling, volume swelling, and density were measured as a function of immersion time. It is observed that the moisture diffusion rate into composites increases with an increase in the jute-fiber-to-epoxy ratio. The type of epoxy used as the matrix appeared to have an influence on the moisture absorption percentages of the composites – the study showed that both water absorption and swellings were higher in the bio-epoxy parts compared to the epoxy parts. The swelling of composites was correlated with an increase in diameters of jute fiber in water and possibilities for the appearance of micro-cracks around fibers in composites were discussed. The data on moisture absorption, thickness swelling, and volume swelling of bio-based composites made from woven jute fibers, and bio-based and ordinary epoxies presented in this article will lead to a better understanding of how these composites react in wet environmental conditions.

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