Porous fibers

Fig. 10. Formation of fibers used in Kuraray man-made leather (a) porous fiber, and (b) a bundle of microfibers.

Fig. 11. (a) Cross-sectional view of substrate with porous fibers and polyurethane sponge, (b) Cross-sectional view of substrate with bundle of microfibers... 

The tubular positive plate uses rigid, porous fiber glass tubes covered with a perforated plastic foil as the active material retainer (Fig. 2). Dry lead oxide, PbO, and red lead, Pb O, are typically shaken into the tubes which are threaded over the grid spines. The open end is then sealed by a polyethylene bar. Patents describe a procedure for making a type of tube for the tubular positive plate (90) and a method for filling tubular plates of lead—acid batteries (91). Tubular positive plates are pickled by soaking in a sulfate solution and are then cured. Some proceed directiy to formation and do not requite the curing procedure. 

Water-Holding Capacity (WHC). AU polysaccharides are hydrophilic and hydrogen bond to variable amounts of water. HydratabUity is a function of the three-dimensional stmcture of the polymer (11) and is kifluenced by other components ki the solvent. Fibrous polymers and porous fiber preparations also absorb water by entrapment. The more highly crystalline fiber components are more difficult to hydrate and have less tendency to sweU. Stmctural features and other factors, including grinding, that decrease crystallinity or alter stmcture, may iacrease hydratioa capacity and solubUity. 

SPAN module. It was mentioned at the beginning that the special polyacrylonitrile fibers of SPAN have a wall thickness of 30 gm, which is considerably thicker than the 8 gm wall thickness of the SMC modules [19]. As a consequence, the presence of stronger capillary effects from the special porous fiber material of the SPAN module would be a reasonable conclusion. Furthermore, the texture of the special polyacrylonitrile fibers is expected to have better surface properties, supporting the permeation of molecules as compared with synthetically modified cellulose. In conclusion, both convection and diffusion effectively contribute to the filtration efficiency in a SPAN module, whereas for the SMC membrane, diffusion is the driving force for molecular exchange, the efficiency of which is also considerable and benefits from the large surface-to-volume ratio. 

The outer tube has a porous fiber tip, which acts as the salt bridge to the analyte solution and the other half-cell. A saturated solution of potassium chloride is in the outer tube. The saturation is evidenced by the fact that there is some undissolved KC1 present. Within the inner tube is mercury metal and a paste-like material known as calomel. Calomel is made by thoroughly mixing mercury metal (Hg) with mercurous chloride (Hg2Cl2), a white solid. When in use, the following half-cell reaction occurs ... 

The commercial silver-silver chloride electrode is similar to the SCE in that it is enclosed in glass, has nearly the same size and shape, and has a porous fiber tip for contact with the external solution. Internally, however, it is different. There is only one glass tube (unless it is a double-junction design—see Section 14.5.3) and a solution saturated in silver chloride and potassium chloride is inside. A silver wire coated at the end with a silver chloride paste extends into this solution from the external lead. See Figure 14.5. The half-reaction that occurs is... 

FIGURE 14.8 Photographs showing the porous fiber strands on various combination pH probes. The arrow points to the strand in each case. Also notice the glass membranes and the protective plastic sheaths. 

The salt bridge for reference electrodes consists of porous fiber tips that provide for the diffusion of ions in and out of this half-cell. 

The Dave model considers a force balance on a porous medium (the fiber bed). The total force from the autoclave pressure acting on the medium is countered by both the force due to the springlike behavior of the fiber network and the hydrostatic force due to the liquid resin pressure within the porous fiber bed. Borrowing from consolidation theories developed for the compaction of soils [23,24], the Dave model describes one-dimensional consolidation... 

Hollow fibers have been tried as liquid-core fibers in spectrophotometry [118] and porous fibers have been well adapted for gas measurements [119,120]. The latter are made of porous polymers, which can trap indicators or reagents in the matrix with a very high permeability of gases and liquids. For liquid applications, porous silica gel has also been used [121],... 

In another application electrospinning [189] of PS-fo-P4VP(PDP)i.o supra-molecules was used to produce internally structured fibers with diameters in the range of 200-400 nm. Due to the block copolymer sample selected, self-assembly resulted in spherical P4VP(PDP) domains with the well-known internal lamellar structure. After the PDP was extracted from the fibers using methanol, porous fibers were obtained [190]. With this method, the thickness of the fibers can be tuned by adjusting the spinning conditions, and the size and nature of the pores can be controlled by the choice of block copolymer and amount of amphiphile. 

For the fiber-metal insulator, the beta-Ti alloys, Ti-13V-llCr-3Al, Ti-2.5Al-16V, and Ti-7Al-4Mo are the current selections, based on existing commercial alloys. Improved Ti alloys or use of a Nb alloy layer next to the Cauldron wall may be necessary to avoid creep at the highest temperatures. A helium sweep gas would be used to remove tritium from the porous fiber-metal channel. 

Chemical vapor infiltration (CVI) is widely used in advanced composites manufacturing to deposit carbon, silicon carbide, boron nitride and other refractory materials within porous fiber preforms. " Because vapor phase reactants are deposited on solid fiber surfaces, CVI is clearly a special case of chemical vapor deposition (CVD). The distinguishing feature of CVI is that reactant gases are intended to infiltrate a permeable medium, in part at least, prior to... 

Fig.1 Schematic cross-section of a porous fiber preform. Reactants diffuse from the preform surfaces toward the center, and are depleted by deposition on fiber surfaces.

The large particle size helps coat porous fibers and produces efficient coatings on corduroy, upholstery, drapery and ticking. 

Most commercial systems like Mustang from Pall and Sartobind from Sartorius make use of functionalized microporous membranes. The fibrils reinforced membranes are (pleated) layered around a porous core. The feed is forced to permeate through the membranes in radial direction. This approach results in high area to volume ratio. The 3M and Mosaic Systems approach is different. Instead of functionalization of a porous support they make use of already functionalized beads, which are embedded in a porous support. In this approach, the beads are responsible for the capacity and selectivity where the porous matrix controls the hydrodynamics. The 3M modules consist of stacked flat sheet or pleated membranes, while Mosaic Systems makes use of porous fibers in which the active particles are embedded (Figure 3.23). 

M. Watanabe, Y. Satoh, and C. Shimura. Management of the water-content in polymer electrolyte membranes with porous fiber wicks. Journal of the Electrochemical Society 140, 3190-3193 1993. 

Kadla, J.F. Gilbert, R.D. Venditti, R.A. Kubo, S. Porous Fiber Manufacture from Natural/ Synthetic Polymer Blends. US Patent 2003212157, 2003. 

Another important area is oriented tapes and webs which are used in the fabrication of porous fiber, fabric, tube, and sheet. These porous articles find applications for protective clothing, waterproof and weatherproof fabrics, gaskets, filter bags, and many other items. 

This model has been tested for packed beds of monosized spheres for porosities as low as e = 0.36 and for porous fiber mats having a porosity as high as e = 0.94. We modify this model to give an improved accuracy for flow through consolidated sandstones or rocks. 

Barth E, Ronningen H, Solheim LF and Saethren B (1986) Bone ingrowth into weightbearing porous fiber titanium implants. Mechanical and biochemical correlations. J Orthopaed Res 4 356-361. 

Figure 16 Conversion from acetyl-DL-methionineto L-methionine by aminoacylase-multilayered porous fiber as a function of the space velocity.

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