Permachor

Perlon Perlon L Permabond Permachor method Permaflex... 

The permachor method is an empirical method for predicting the permeabiUties of oxygen, nitrogen, and carbon dioxide in polymers (29). In this method a numerical value is assigned to each constituent part of the polymer. An average number is derived for the polymer, and a simple equation converts the value into a permeabiUty. This method has been shown to be related to the cohesive energy density and the free volume of the polymer (2). The model has been modified to liquid permeation with some success. 

The Monsanto Company developed the Permachor method to predict permeation through polyethylene and other polymers. The prediction is... 

Permeation and dissolution are the main processes determined by diffusive mass transfer. Permeation of polymers by small molecules depends on their solubility and diffusivity. For both quantities reasonable estimations are possible if some basic data of the permeating molecules (e.g. critical temperature and collision diameter) and of the polymer (structure, glass transition temperature, crystallinity) are known. For the estimation of the permeability of thin layers (films) an additive quantity, the permachor, is available. 

The Permachor, an additive molar function for the estimation of the permeability... 

In 1986 Salame introduced a new physical parameter re, for which he coined the name (specific) Permachor. It is defined by the equation... 

Salame found that the product Nrc, the Molar Permachor (II) is an additive function ... 

Table 18.11 gives the list of group contributions to the molar permachor. 

A disadvantage of the permachor method is that in case of different gases a set of values for P (298) and for s should be known. It must be advised therefore to calculate first of all log P(298) for nitrogen (taking this gas as the standard gas) and then to apply the relative P-values given in Table 18.9 in order to estimate the P-value of the relevant gas. For other temperatures the permeability can be estimated by means of Eq. (18.21). For this Ep must be known ( AHS + Fd)-... 

The re-values calculated by means of the Molar Permachor are valid for amorphous polymers. For semi-crystalline and oriented polymer films a correction must be made. Salame recommends for semi-crystalline polymers the following expression ... 

Parallel plates, 527 Parallel polarised light, 299 Paramagnetic, 355 Pardox of Kauzmann, 151 Partially immobilising sorption, 682 Partly oriented yams, 483 Peclet number, 56,59 P-electron conjugation, 140,161,183 Penetrant, 655 Performance properties, 52 Permachor, 676 Permeability, 656, 673, 676 coefficient, 656 magnetic, 287 of polymers, 675 Permeation coefficient, 673... 

T, = IT,(groups)—permachor by the Salame group-contribution technique,... 

The most commonly used empirical method for estimating the permeability, however, is the "permachor" method of Salame [21,74-78]. An additive property, which is called the permachor and represented by the Greek letter n, is defined, and P is expressed in terms of n. The values of 7t are obtained empirically, and are assumed to quantify the key physical factors believed to determine the permeabilities of polymers, namely their cohesive energy densities and their fractional free volumes. The P s (in DU) of a large number of polymers to 02, N2 and... 

Permachor n. A concept of M. Salame (1961), who discovered that the permeation rates of many (though not all) organic liquids through polyethylene (PE) films could be estimated with the equation ... 

Figure 11.11 Correlation of gas permeability and permachor. (Reprinted with permission from M. Salome, Polymer Eng. Sci., 26 22, 1543, 1986)...

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