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.

No abstract

No abstract

No abstract

Silica-epoxy nanocomposites are very common among nanocomposites, which makes them very important. Several researchers have studied the effect of nanoparticle’s size, shape, and loading on mechanical behavior of silica-epoxy nanocomposites. This paper reviews the most important research done on the effect of nanoparticle loading on mechanical properties of silica-epoxy nanocomposites. While the main focus is the tensile behavior of nanocomposite, the compressive behavior and flexural behavior were also reviewed. Finally, some of the published experimental data were combined in the graphs, using dimensionless parameters. Later, the best fitted curves were used to derive some empirical formulas for mechanical properties of silica-epoxy nanocomposites as functions of weight or volume fraction of nanoparticles.

Liquid imbibition into polymer wicks, where a clear liquid front can be seen rising during the wicking process, is modeled using the concepts of flow in porous media. The flow of liquid behind the moving liquid front is modeled using the physics of single-phase flow in a porous medium where the Darcy's law is combined with the continuity equation and a capillary suction pressure is imposed at the liquid front. A novel numerical simulation PORE-FLOW V V C based on the finite element/control volume method is proposed to model such imbibitional flows in wicks of complex shapes. A validation of the simulation is obtained by achieving an excellent comparison of its predictions with an experimental result, an analytical solution, and the Washburn equation for the case of wicking against gravity in a cylindrical wick. The simulation is also used to predict a case of two-dimensional (2D) wicking in the altered cylindrical wicks with two different cross-sectional areas. Once again an excellent match is obtained with the experimental results, while analytical solutions for the single and double cross-section cases along with the Washburn equation fail to predict the 2D wicking. Later, some other types of altered wicks with sharp changes in their cross-sectional areas were analyzed numerically for their wicking behavior. It was observed that the height of liquid front in a vertical wick as a function of time, which is proportional to the history of liquid imbibed, is strongly dependent on the extent of reduction in the wick cross-sectional area as well as its location vis-a`-vis the wick entrance.