Microporous fibers

Figure 3 c. HRTEM image of a cross-section of a carbon fiber after propylene pyrolysis the black line represents the boarder between the lamellar pyrocarbon (at the top) and the microporous fiber (at the bottom). 

PCA [Precipitation with a compressed anti-solvent] A process for making a solid with unusual morphology by spraying a solution of it into a supercritical fluid. The process resembles spray drying into a supercritical fluid. Used for making microspheres, microporous fibers, and hollow microporous fibers. 

AMT holds U.S. patents on several membranes, including the basic patents on the coated microporous fibers used in the oxygenated system. 

Microporous fiber have been produced using the following method." Polypropylene is filled with 25 wt% calcium carbonate. After extrusion, the fiber is stretched at 150°C and calcium carbonate is dissolved by an acid treatment. Pore sizes from 0.01 to 0.02 um are obtained depending on the type of acid treatment and the stretching ratio. Crystallinity decreases as the stretching ratio decreases and the fiber diameter increases after acid treatment because of shrinkage. 

The available preparation routes for porous polymeric fibers with particulate material incorporated require an additional process step to introduce the desired porosity [163]. After the preparation of the matrix comprising particulate material, either the particulate material is removed from the nonporous fiber or the nonporous fiber is stretched resulting in porous fibers. In the latter case, a microporous fiber comprising particles having a certain sorptive function can be obtained. 

Keywords microporous film, microporous hollow fiber, microporous fiber, filler, uniaxial stretching, biaxial stretching, permeation, water vapor permeation, air permeation, tortuosity factor. 

Fig. 5.11 A microporous fiber is shown in the SEM and TEM micrographs. The fiber is seen to have voids in the fracture views (A and B), but the voids are not clearly defined. The outer fiber surface (C) also has voids, and particles are observed within some of them. TEM micrographs of the fiber cross sections (D and E) reveal voids (white regions) that are smaller in size in an outer micrometer sized band than those in the central portion of the fiber.

The first applications employed symmetric microporous hollow fibers in which the fiber materials were hydrophobic or hydrophilic. The membrane liquid may or may not wet the pores spontaneously. To separate a gas mixture in a permeator employing symmetric hydrophobic microporous fibers with gas-filled pores and nonwetting aqueous liquid membranes (Figure 2a), the liquid membrane pressure (PjJ is maintained higher than those of the feed gas (Ppo) and the sweep gas (Psg) to prevent their dispersion in the membrane liquid (4), However, the excess pressure of the liquid membrane over that of either gas stream must be less than the breakthrough pressure for the membrane liquid (which is a function of the membrane material, pore size, and the interfacial tension between the pore fluid (here, gas) and the membrane liquid). For other fibers and configurations. Figures 2b and 2c provide appropriate details. 

Another pilot-scale evaluation of a SLM with hollow fibers was made by Dworzak and Naser (66). The method was applied to low-level radioactive wastes with 333 PP microporous fibers which had a surface area of 3.6 m. ... 

Zeolites (NaA, Composite Microporous fiber monolith Plate tube hollow... 

ZSM-5, etc.) Carbon Symmetric/ Microporous fiber Tube hollow fiber... 

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