Vapors, rubber permeability

Another advantage of nitrile rubbers that contain PVC combinations is that they are non toxic and not influenced by mineral oils. Water vapor permeability is also good. 

Nonlinear, pressure-dependent solubility and permeability in polymers have been observed for over 40 years. Meyer, Gee and their co-workers (5) reported pressure-dependent solubility and diffusion coefficients in rubber-vapor systems. Crank, Park, Long, Barrer, and their co-workers (5) observed pressure-dependent sorption and transport in glassy polymer-vapor systems. Sorption and transport measurements of gases in glassy polymers show that these penetrant-polymer systems do not obey the "ideal sorption and transport eqs. (l)-(5). The observable variables,... 

Table 2 shows the properties of mat-like paving material using mill-ground and shredder-cut powdered rubbers. The mat-like paving materials have good cushioning property, skid resistance, water or vapor permeability, sound absorption and weatherability. 

Counteraction to swelling depends on the rate of diffusion of water molecules through the film, i.e., the vapor permeability of the coatings. A nonpolar hydrophobic rubber or paraffin film has a low vapor permeability, while a hydrophilic gelatin or skin-glue... 

The vapor permeability of thermoplastic rubbers with polydiene midblocks is similar to that of the rubber which forms the midblock. However, as the fraction of endblock is increased, as for example by adding endblock compatible resins, the permeability is somewhat reduced. Conversely, as the rubber phase fraction is increased, for example by adding a midblock compatible oil, the nitrogen permeability increases. While the permeability of thermoplastic rubbers is about the same as SBR, natural rubber, and poly butadiene, it is much higher than polyolefins and other materials used in packaging. This can be an advantage where high air or moisture vapor transmission is desired. 

Permeation rates are dependent on the ehemieal makeup of the eontamination. This ineludes the size of the eontaminant (how large or small the moleeule or partiele is) and on the pore size of the proteetive material (for instanee, impermeable rubber suits, tyveks, or eotton eoveralls). Chemieal eharaeteristies (i.e., polarity, vapor pressure, pH) of both the eontaminant and the proteetive material also determine permeability. Keep in mind that gases, vapors, and low-viseosity liquids tend to permeate more readily than high-viseosity liquids or solids [2],... 

Subramaniam, 1988]. Hydrochlorination, usually carried out at about 10°C, proceeds by electrophilic addition to give the Markownikoff product with chlorine on the tertiary carbon (Eq. 9-33) [Golub and Heller, 1964 Tran and Prud homme, 1977]. Some cyclization of the intermediate carbocation (XXVI) also takes place (Sec. 9-7). The product, referred to as rubber hydrochloride, has low permeability to water vapor and is resistant to many aqueous solutions (hut not bases or oxidizing acids). Applications include packaging film laminates with metal foils, paper, and cellulose films, although it has been largely replaced by cheaper packaging materials such as polyethylene. 

Equation (2.79) expresses the driving force in pervaporation in terms of the vapor pressure. The driving force could equally well have been expressed in terms of concentration differences, as in Equation (2.83). However, in practice, the vapor pressure expression provides much more useful results and clearly shows the connection between pervaporation and gas separation, Equation (2.60). Also, the gas phase coefficient, is much less dependent on temperature than P L. The reliability of Equation (2.79) has been amply demonstrated experimentally [17,18], Figure 2.13, for example, shows data for the pervaporation of water as a function of permeate pressure. As the permeate pressure (p,e) increases, the water flux falls, reaching zero flux when the permeate pressure is equal to the feed-liquid vapor pressure (pIsal) at the temperature of the experiment. The straight lines in Figure 2.13 indicate that the permeability coefficient d f ) of water in silicone rubber is constant, as expected in this and similar systems in which the membrane material is a rubbery polymer and the permeant swells the polymer only moderately. 

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... 

Membranes for vapor removal from air have a structure similar to the prism membrane, but they are prepared on a different principle.Aromatic PEI is used to produce a porous substrate membrane by the dry-wet phase inversion method. This polymer was chosen over PS/PES because of the higher durability of PEI to organic vapors. Unlike an asymmetric PS substrate for the prism membrane, the top layer of asymmetric PEI membrane has a large number of pores, the size of which is equivalent to those of UF membranes. When a layer of silicone rubber is coated on the top layer of the porous substrate membrane, the silicone rubber layer will govern the selectivity and the porous support will provide only mechanical strength to the composite membrane. Because the permeabilities of water and organic vapors through the silicone... 

Rubber Property-Vapor Transmission of Volatile Liquids Oetermining Gas Permeability Characteristics of Plastic Film and Sheeting Water Vapor Transmission of Organic Coating Films... 

The potentiometric oxygen determination is suitable in an analogue way for the examination of the oxygen permeability of rubber and synthetic tubes [68] or membranes [69], in which the use of an additional solid-electrolyte cell is very helpful for the oxygen-dosage ( oxygen pump ). The method can also be modified in such a way that, eg, the permeability for water vapor is measurable. 

PERMEABILITY OF RUBBERS TO VAPORS AND CASES 7.6.1 Principle of the Transfers... 

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