Air Force

Adsorption, absorption, and separation fibers with greater capacity

A capillary slit along the length of the fiber greatly increases its performance in a broad variety of filtration applications

Materials Medical & Biotechnology Environmental

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A cross-sectional view of a fiber (153) with six-axial capillary slits (158) using parallel lobes to form a continuous capillary slit. Fluids can enter at the ends of the lobes (148) or through the slits (160). While this design has six slots, the numbers can range from 1 to many.

Air Force scientists have developed new fluid separation devices with high efficiency absorptive and adsorptive materials. An axial capillary slit through the side of a non-porous hollow fiber acts as a capillary into the fiber and dramatically increases the efficiency and usefulness of such hollow fibers over such fibers having capillary entrances in only the ends.

Specifically, the rate of fluid movement through the axial capillary slit and the total fluid capacity of the hollow fiber are significantly increased. This approach effectively decouples the interior fiber volume from the size of the capillary entrance. That is, by employing capillaries formed by overlapping lobes instead of the ends of fiber lobes, it is possible to create a true hollow fiber with significantly increased capacity, increased rate of adsorption or separation, with increased selectivity, and which is less sensitive to pressure fluctuations.

The interior wall surfaces of the axial slit-shaped capillary, the wall surface of the internal fiber compartment as well as the exterior surface of the hollow fiber can each have a surface characteristic selected from the group consisting of hydrophilic, oleophilic, hydrophobic and oleophobic, or a combination of these. Such diversity allows these fibers to be used as selective absorption materials to absorb fluids or to separate liquids from one another.

Used as discrete fibers or in woven, braided, knitted, felted, filament wound or matted form, these fibers can be used as very efficient particle filtration, absorptive materials, adsorptive materials, time-release, or separation devices. When used for particle filtration, the capillary slits are nearly impossible to clog with particulates that are spherical in shape. This type of particulate filter is easy to clean by merely pressurizing the interior of the fibers and back-flushing.

When used as a time-release device, the material that has been previously placed inside the hollow fiber is accessible along the entire length of the fiber simultaneously making this a relatively fast-release device. This is in contrast to conventional hollow fibers in which the material on the inside of the fiber is accessible only through the ends and release is controlled by diffusion. When one or both ends of the hollow fibers with an axial capillary slit connecting to a manifold, a separation device with essentially infinite capacity results. For gas or liquid injection, these devices are ideal because the fibers can be in intimate contact with the second fluid along the entire length of the fiber.

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