Polymer permeability effect

At strains >10%, when the polymer structure has begun to collapse, gas loss, by diffusion through the cell faces of closed cell foams, may contribute to the creep. The effect of this on the creep of LDPE and EVA foams was determined (266). The foam diffusivity for air was predicted from the polymer permeability P and the foam density p using ... 

Considering heterogeneous models for the film structure, we realize that if PVC with its low permeability were the continuous phase, there should only be small increases in permeability with the addition of EVA polymer. Such effects have been observed for a system of butadiene-based polymer modifier added to PVC to increase the impact strength (1). Addition of 15% modifier increased the permeability less than 10%. Electron micrographs of this film showed that the butadiene-based modifier was dispersed in the PVC phase. 

The figure also shows that the highly permeable zeolite only has a large effect on polymer permeability when the percolation threshold is reached. That is, useful... 

Eigure 5.48 shows the permeability effect on the maximum permeability reduction factor, Ekrmax, predicted from Eq. 5.37. This figure shows that Fbjnax decreases with permeability, which is consistent with the observation that the polymer retention decreases with permeability, as shown in Figure 5.46. The laboratory-measured permeability reduction data at the polymer concentration... 

Figure 5.49 shows the polymer concentration effect on the permeability reduction factor, F, predicted from Eq. 5.36. This figure shows that F is a weak function of polymer concentration, and it increases shghtly within a low concentration range. Concentration quickly reaches a plateau. This effect is consistent with the polymer adsorption shown in Figure 5.43. 

In UTCHEM, the viscosity of the aqueous phase that contains the polymer is multiplied by the value of the polymer permeability reduction factor, F r, to account for the mobility reduction. In other words, water relative permeability, km, is reduced, whereas oil relative permeability, k , is sometimes considered almost unchanged. The reason is that polymer is not soluble in oU, so it will not reduce effective oil permeability. The mechanism of disproportionate permeability reduction is widely used in gel treatment for water shut-off. Many polymers and gels can reduce permeability to water more than to oil or gas. 

In alkaline-polymer flooding, in addition to the polymer mobihty control effect, the precipitation (e.g., Ca(OH)2 and Mg(OH)2) caused by alkah also helps to increase sweep efficiency. Precipitates formed by alkalis may be able to flow through pores without blocking any flow, or reduce both oil and water permeabilities. However, precipitates combined with polymer can effectively reduce water permeability because polymer is in the water phase. 

In ASP flooding, alkaline, surfactant, and polymer have different effects on relative permeabilities. Table 13.2 shows our attempt to summarize these effects compared with waterflood. From Table 13.2, we can see that the effect of alkaline flood in terms of emulsification is similar to the polymer effect, whereas its effect in terms of IFT is similar to the surfactant effect. Less rigorously, we may say that only polymer reduces k, and only surfactant reduces IFT. In ASP flooding, the viscosity of the aqueous phase that contains the polymer is multiplied by the polymer permeability reduction factor in polymer flooding and the residual permeability reduction factor in postpolymer water-flooding to consider the polymer-reduced k effect. Then we can use the k curves (water, oil, and microemulsion) from surfactant flooding or alkaline-surfactant flooding experiments without polymer. 

Effect Of Molecular Structure on Polycarbonate Oxygen Permeability. Permeability measurements on a series of structurally different aromatic polycarbonates indicate a strong relationship between monomer structure and polymer permeability. A major part of this study investigated properties of polycarbonates which were prepared from variously substituted bisphenols. The polycarbonate samples are based upon bisphenol monomers which differ from 2,2-bis(4-hydroxy-... 

Vu et al. [122] incorporated CMS materials into polymers to form MMM films for selective gas separations. The CMS, formed by pyrolysis of a PI precursor and exhibiting an intrinsic CO2/CH4 selectivity of 200, was dispersed into a polymer matrix. Pure-gas permeation tests of such MMMs revealed the CO2/CH4 selectivity was enhanced by as much as 40%-45% relative to that of the pure polymer. The effective permeabilities of fast-gas penetrants (e.g., O2 and CO2) through these MMMs are also improved relative to the intrinsic permeabilities of the unmodified polymer matrices. For a CO2/H2 gas mixture, the CO2 will be the fastest permeating component, and H2 will be retained on the feed side to avoid repressurization, in which case the polymer matrix dictates the minimum membrane performance. Properly selected molecular sieves can only improve membrane performance in the absence of defects. The polymer matrix must be chosen so that comparable permeation occurs in the two phases (to avoid starving the sieves) and so the permeating molecules are directed toward (not around) the dispersed sieve particulates. 

As noted earlier in the context of Tables 20.4-1, 20.4-2, and 20.4-3, the ratio of pure component permeabilities at an arbitrary pressure is a useful indication of the selectivity of a candidate nnembrane for the chosen gas pair. Never less, because of a variety of factors, the actual selectivity and productivity observed in the mixed gas case may be somewhat different than predicted on the basis of the pure eomponent data. One of these factors, illustrated in Fig. 20.4-4, is important for low- and interr iate-pressure applications and is believed to be due to competition by mixture components for unrelaxed molecular-scale gaps between glassy-polymer chain segments. As shown in the left-hand side of the figure, the presence of a second component B can depress the observed permeability of a component A relative to its pure component value at a given upstream driving pressure of component A. H< n and coworkers note that the permeability of a membrane to a component A may be reduced due to the sorption of a second component B in the polymer which ... effectively reduces the microvoid content of the film and the available diffiision paths for the nonreactive gases. ... 

The second part is devoted to the characterization of polymers properties. Effective utilization of a polymeric material in agriculture and the food industry depends on their physical form, porosity, solvation behavior, diffusion, permeability, surface properties, chemical reactivity and stability, deterioration and stability, and mechanical properties. Any such features are crucial and depend on the conditions employed during preparation and must be considered during the design of a new reactive polymer. 

Theoretical approaches on the barrier properties of nanocomposites beat fillers as impermeable nonoverlapping particles and assume no permeability changes in the polymer matrix. Effectively, this means that the permeability of the composite will be smaller than the permeability of the matrix (unfilled polymer) by a factor equal to path tortuosity in the composite (simply assuming that the penetrant path cannot cross any filler particles). This path tortuosity was calculated by Nielsen for completely aligned filler particles (aU fillers have then-larger surface parallel to the film surfaces, but there is no order in the filler center of mass), and its contribution to the composite permeability was derived to be... 

Other important parameters (such as permeant solubiUty changes and polymer crystallinity effects) when it comes to predicting permeability changes upon nanocomposite formation. 

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