Fluoropolymer membranes polymerization

ACPS), have also been used to fabricate microporous membrane [24-29], However, among these techniques, TIPS and IP are the two most commonly employed methods in the fabrication of polymeric membranes including fluoropolymer membranes. One of the main difficulties that limit the successful casting of phase inversion membranes is the lack of a predictable and systematic method in the selection of solvent and nonsolvent systems [30],... 

Surface modification of the polymeric membranes via molecular design is one of the most versatile means to improve the surface properties without affecting bulk properties. Surface modification of fluoropolymer membranes, especially for fully fluorinated polymer membranes, such as PTFE membranes, has been of particular interest, due to their physical and chemical inertness. Surface modification of fluoropolymer membranes can be classified into two categories surface coating and surface grafting. 

Due to their physical and chemical inertness, fluoropolymers are resistant to UV irradiation in the wavelength range of 100-400 nm. It is difficult to directly activate the fluoropolymer membrane surface via UV initiation due to its inert property. A photo-initiator, such as benzophenon, is usually needed to initiate the photo graft polymerization process from the fluoropolymer membrane surfaces [130]. Benzophenon was decomposed into radicals. The free radicals are transferred to the fluoropolymer membrane and hydrogen abstraction leads to the generation of initiating radicals. Benzophenon can be coated onto the membrane surface by dipping the membrane in benzophenon solution in an adsorption process [130,131]. This method could... 

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

A new development reported by Li and Sirkar [141] for MD-based desalination makes use of polypropylene hollow fibers coated with a plasma polymerized sUicone-fluoropolymer. This ultrathin coating on the outside of the fiber was water vapor permeable and was instrumental in decreasing the susceptibility of the composite membrane to wetting and fouling. They reported stable water vapor fluxes between 41 and 79 kg h for runs lasting up to 400 h. 

Membranes which may be used in the removal of alkali metal ions by electrodialysis are those which are impermeable to anions, but which allow the flow therethrough of cations. Such cation-selective membranes should, of course, possess chemical durability, high resistance to oxidation and low electrical resistance in addition to their ion-exchange properties. Homogeneous-type polymeric membranes are preferred, for example, network polymers such as phenol, phenosulfonic acid, formaldehyde condensation polymers and linear polymers such as sulfonated fluoropolymers and copolymers of styrene, vinyl pyridine and divinylbenzene. Such membranes are well known in the art and their selection for use in the method of the invention is well within the skill of the art. 

There are a few points to be kept in mind. The liquid membrane must be nonvolatile since it is subjected to vacuum on the permeate side and can evaporate on the feed side and be lost to the feed solution (Figure 8.1.49(d)). Further, wetting of the porous membrane structure spontaneously by the membrane liquid present outside requires that the surface tension of the membrane liquid should be equal to or lower than the critical surface tension of the polymeric or ceramic substrate being employed. For example, y,. for polypropylene (PP) is -33 dyne/cm. Many organic liquids will spontaneously wet it. However, y,. values for various fluoropolymers (FPs) are usually <25... 

In general, research on classes of materials is connected with that on materials with specific properties but includes somewhat more general research on composites, polyurethanes, epoxies, fluoropolymers, ferroelectric liquid crystals (especially those with fast switching times), polymer-polymer miscibility, double network elastomers, crystallization in polymers, polymeric Langmuir-Blodgett and other multilayer films, and polymer-stabilized synthetic membranes. 

Li and Sirkar (2004, 2005) reported on novel hollow-fiber membranes and modules for use in both DCMD and VMD configurations. The presented new types of membranes were commercial porous PP hollow fibers (Accurel MEMBRANA, Wuppertal, Germany) of different dimensions and thicknesses coated with a variety of ultrathin microporous silicone-fluoropolymer layer on their external surface by plasma polymerization at Applied Membrane Technology (AMT) Inc. (Minnetonka, MN). The fibers were arranged in a rectangular cross-flow module design for the hot feed to flow over the outside surface of the fibers and to reduce the temperature polarization effect. Both the DCMD and VMD... 

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