Permeability, Permeation blend

Barrier polymers, 3 375-405 applications, 3 405 barrier structures, 3 394-399 carbon dioxide transport, 3 403 flavor and aroma transport, 3 403-405 health and safety factors, 3 405 immiscible blends, 3 396-398 large molecule permeation, 3 388-390 layered structures, 3 394-396 miscible blends, 3 398-399 oxygen transport, 3 402 permanent gas permeation, 3 380-383 permeability prediction, 3 399-401 permeation process, 3 376-380 physical factors affecting permeability, 3 390-393... 

Permeability measurements for polymer blends prepared by mixing different latices have been reported by Peterson (14). Interpreting transport data for such heterogeneous systems as polymer blends is extremely difficult, however (3, 9,15). The main purpose of the present investigation is, therefore, to study the applicability of gas permeation measurements to characterize polymer blends and not to evaluate the different theoretical models for the permeation process in heterogeneous polymer systems. 

Polymers Mixed by Milling. The effect of EVA concentration in the blends on gas permeation and light transmission through the film was studied. The permeability and the diffusion coefficients at 50 °C for the penetrants helium, argon, and carbon dioxide are shown in Figures 1, 2,... 

Earlier work done in these laboratories has shown that polymer blends wherein the barrier polymers are dispersed as thin platelets parallel to the surface of the fabricated article, have significantly improved permeability barrier properties than the conventional "homogeneous", uniform, dispersions (1,2). The high barriers demonstrated were then achieved by blending 15-20% polyamides with a linear polyethylene, which achieved performance comparable to that obtained by adding as much as 50% nylon by conventional blending. While this performance has been satisfactory for a variety of applications, some of the more demanding uses require that the barrier polymer be used more efficiently. Described here are such blend compositions which show substantial resistance to permeation of hydrocarbon solvents and their mixtures. 

Analogously, correlations exist between the coefficient of water permeabihty k and that of capillary absorption S, but these lose their validity if the surface of the concrete is subjected to a hydrophobic treatment, which will reduce considerably capillary absorption but not permeation. For concrete obtained with Portland cement, correlations between the coefficient of water permeability (k) and conductivity (o = 1/p) measured for a given value of relative humidity are available. On the other hand, conductivity varies greatly in concrete made with blended cements or carbonated concrete, while there is no significant change in water permeability. 

Figure 4.44 shows the water permeability as measured parameter, time (s), by Figg s methodi 1 of dry-cured EVA-modified mortars with blended cements containing various mineral admixtures. According to this method, the measured parameter is the time taken for a standard volume of water to be permeated into the specimen through a 10 nun diameter x 40 mm deep hole.P 1 An increase in the measured parameter of EVA-modified mortars with the blended cements indicates a decrease in the water perme-ability, and increasing polymer-cement ratio decreases the water permeability by a factor of 10 or more. 

Effect of aging on the permeability and molecular motion of the membranes of PMSP, poly(TMSP-co-PP) and blend of PMSP/PPP Glassy polymers, such as PMSP, are nonequilibiium materials and their permeation and sorption properties drift over time as thermally driven, small-scale polymer segmental motions cause a relaxation of nonequilibrium excess free volume. The microcavities of large size which are present in PMSP membrane have been considered to be responsible for the decay of C h and the gas permeability (4). Therefore, it is possible to stabilize the gas permeability by control the C by copolymerization or blending with the other acetylene derivatives such as PP and PPP, respectively. 

The gas permeation parameters have also been reported for polymers obtained via ether reaction of epoxy and diamines [57,58], for polymer blends with acetylene-terminated oligomer [73,74] and internal acetylene polyimide [72,75]. The gas permeability of cross-linked internal acetylene-containing polymer, 6FDA-TeMPD/p-intA (4 1) declines from 612 to 186Barrer, while the selectivity, a(C02/CH4) increases from 14 to 25 at 35°C and lOatm [75]. Moreover, this cross-linked 6FDA-TeMPD/p-intA (4 1) membrane is still stable under CO2 pressure of about 47 atm. 

Table 13.5 CO2 and N2 permeability (P), diffusion (D) and sorption (S) coefficients obtained for three Pebax 1657-PECEPi blends by using the gas permeation method in...

The permeation data (Figure 13.7) indicate first a reduction in CO2 permeability from that of a pure Pebax 1657 membrane, then a steady increase in CO2 permeability. The highest performances were obtained with a blend containing 20wt.% PEG300 the CO2 permeability reached 128 Barrer and the CO2/N2 ideal selectivity was 80. 

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