Rubbery polymer membrane application

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

Spiral-wound modules are much more commonly used in low-pressure or vacuum gas separation applications, such as the production of oxygen-enriched air or the separation of organic vapors from air. In these applications, the feed gas is at close to ambient pressure, and a vacuum is drawn on the permeate side of the membrane. Parasitic pressure drops on the permeate side of the membrane and the difficulty in making high-performance hollow fine fiber membranes from the rubbery polymers used to make them both work against hollow fine fiber modules for such applications. 

In the separation of vapor/gas mixtures, rubbery polymers, such as silicone rubber, can be used to permeate the more condensable vapor components, or glassy polymers can be used to permeate the smaller gases. Although glassy, gas-permeable membranes have been proposed for a few applications, most installed plants use... 

To effectively use ionomer membranes for dehydration applications it is necessary to understand water transport in these polymers. Molecular diffusion in swollen polymers does not follow the classical Fickian behavior. Fickian behavior is observed for diffusion of gases at low pressure through rubbery polymers at temperatures well above Tg. Under these conditions permeability is independent of gas pressure. Glassy polymers show pressure dependent permeabilities. These effects disappear at higher pressures and can be explained by dual mode theory. Similarly, permeabilities of vapors such as water in hydrophobic or mildly hydrophilic membranes are independent of water vapor pressure. 

Polyvinyl acetate (PVAc) is another rubbery polymer used in mixed-matrix research. Its flexible nature helps to prevent void formation at the solid-polymer interface. Although it may not have practical industrial applications, PVAc aids in developing proof-of-concept associated with mixed-matrix membranes. Zeolite 4A-PVAc membranes have been proven to enhance membrane selectivity in mixed-matrix membranes with only 15 vol% zeolite " however, the permeability is lower than predicted presumably due to matrix rigidification. The rubbery nature of PVAc allows for more polymer relaxation at the solid-polymer interface as compared to the case with traditional, glassy polymers." ... 

The importance of regularity, polarity, and chain stiffness becomes apparent in the uses of polyethers. Of the common polyethers, only polyformaldehyde, poly(ethylene oxide), and the polymer based on 2,2-dichloromethylpropylene-1,3-oxide are crystalline. Since poly(ethylene oxide) is water soluble, only the remaining two polyethers are useful structural materials. Phenoxy, phenylene oxide, and sulfone polymers are useful thermoplastics because the chain stiffness contributed by aromatic rings in the backbone raises 7 well above room temperature. Polysulfones are used in the manufacture of membranes for gas separations (Section 13.6). The aliphatic ether backbone is more conducive to low 7 s that are suitable for rubbery applications. Fully cured epoxy resins are dimensionally stable network polymers. Low-molecular-weight polymers of ethylene oxide [often abbreviated as PEG for poly(ethylene glycol)] are often listed as ingredients of... 

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