Permeability of Simple Gases and Permachor

TABLE 4.11 Relative Permeability Parameters for Various Gases 

Experimental values of permeability of nitrogen at room temperature through various elastomers, semicrystalline, and amorphous polymers showed great variation depending on the polymer. Thus, silicone rubber showed the highest permeability of 10 cm /s-Pa, whereas poly(vinylidene chloride) showed the lowest of 4 x 10 cm /s-Pa. Table 4.11 provides rules of thumb on relative permeability and activation energy. 

A more accurate way of predicting the barrier properties of polymers is to correlate polymer structure and morphology to permeability. Salame (1986) introduced the idea of the pemachor, %, which assigns a value for the polymer chain based on the specific values for the various structural units of that chain. Although three gases were studied extensively (N2, O2, and CO2), the approach can be extended to other gases as well. The permeability is defined as 

TABLE 4.12 Pre-exponential Permeability Factor, E, and Scaling Factor, s 

For semicrystalline materials, with crystallinity the permachor should be calculated based on the amorphous 3ta as follows  

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