Water vapor permeability, various polymers

Table 7-4. Permeability Coefficients of Gases and Water Vapor in Various Polymers at 20° C. The Gas Passage, Am, Is Measured in cmi. Barex Is a Graft Copolymer of Acrylonitrile Methyl Acrylate on Nitrile Rubber. Lopac Is a Copolymer of Methacrylonitrile and Styrene.

FIGURE 2.10 Theoretical predictions based on path tortuosity [eq. (2.9)], as a function of (a) filler aspect ratio a = 1 to 1000 (b) filler aspect ratio and alignment (5 = 1 perfect smectic alignment—dashed lines S = 0 random orientation —solid lines) (c) filler aspect ratio for a constant volume fraction (pv = 5%. (d) Comparison of the same theoretical predictions (parameters as indicated) with experimental values for water vapor permeabilities in various polymer-montmorillonite nanocomposites. (From Refs. 39-41.)... 

Table 8. Comparison of the Permeabilities of Various Polymers to Water Vapor ...

Figure 2.60 Permeability of water vapor as a function of temperature through various polymer films.

For example, consider a soft drink or soda bottle. What are the requirements Cheap Strong enough to contain up to 2L of soda. Optically clear. And very important, a barrier for 0O2, because carbonated beverages taste flat once the concentration of carbon dioxide falls too low. Table 8-1 lists the permeability of various polymers to C02 as well as to oxygen and water vapor. 

The water ingress properties of various polymers can be assessed by values of their permeability coefficient and the diffusion constant of water (Table 15.13). The permeability coefficient is defined as the amount of vapor at standard conditions permeating a sample that is 1 cm2 and 1-cm thickness within 1 s with a pressure difference of 1 cmHg across the polymer. The diffusion coefficient is a measure of the ease with which a water molecule can travel within a polymer. There is a wide variation in the maximum amount of water absorbed by polymeric materials. Certain systems have very low absorption at lower temperatures, but the rate of absorption increases significantly at higher temperatures. 

The insoluble cellulose derivatives utilized for permeation control of various species (e.g. oxygen and water vapor transport in coated pharmaceuticals, contact lenses, packaging, or water and solute transport through semi-permeable membranes in reverse osmosis, as well as drug release from reservoir systems) differ considerably in their permeability characteristics according to the type and extent of substitution, as well as their molar mass. However, very few comparative data are available from the literature on the polymers actually used in biological applications. Recently, new results have been published. Thus, Sprockel et al. [142] determined the water vapor transmission through various CA, CAT, CAB and CAPr films at different relative humidities (Table 22). 

A comparison of moisture vapor permeation through various polymers can be seen in Table 3.5. Notice that PCTFE is only second to FEP and both are among the most resistant plastics to water vapor permeation. Permeability data can be found in Appendixes I through IV. 

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