Plastics permeability data

The choice of closure materials is generally dependent on the required processing conditions and die nature of die contents and closure system (i.e. the application and sealing method). 

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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. 

Figure 10.84. Permeability coefficient, P of plasticized PVC vs. temperature and plasticizer content. [Data from Lelchuk S L, Sedlis V l,J. Appl. Chem. USSR, 30, 1106-1113, 1957.]...

Typical permeability data are shown in Table 4.5 (70) for a range of elastomers, amorphous plastics, and semicrystalline plastics. In general, permeabihty decreases from elastomers to amorphous plastics to semicrystalline plastics. 

The journal and patent literature was searched to identify the 87 polymers used in this work. They include members from the polymers, their structure, and gas transport properties are provided in the Appendix. Carbon dioxide is reported to permeate many polymers by a dual mode transport mechanism (13). It has also been noted that COj has a plasticizing effect on some polymers leading to decreased permselectivity at high pressure (14). For these reasons we have preferentially used pure gas permeability data obtained at 10 atm CO2 and 35°C. 

Plasticization and Other Time Effects Most data from the literature, including those presented above are taken from experiments where one gas at a time is tested, with Ot calculated as a ratio of the two permeabihties. If either gas permeates because of a high-sorption coefficient rather than a high diffusivity, there may be an increase in the permeabihty of all gases in contact with the membrane. Thus, the Ot actually found in a real separation may be much lower than that calculated by the simple ratio of permeabilities. The data in the hterature do not rehably include the plasticization effect. If present, it results in the sometimes slow relaxation of polymer structure giving a rise in permeabihty and a dramatic dechne in selectivity. 

The main reason for producing multi-layer co-extruded films is to get materials with better barrier properties - particularly in regard to gas permeation. The following Table shows the effects which can be achieved. Data on permeability of plastics are also given in Figs 1.13 and 1.14. 

ATII cells, when plated on permeable supports or plastics under appropriate culture conditions, acquire features of type I cell-like phenotype and morphology [30, 57, 80], Although isolation of ATI pneumocytes from rat lungs has recently been reported with some success [28, 48, 81], development of confluent ATI cell monolayer with electrically tight characteristics has not been reported yet. It should be noted that unlike many other cells in primary culture, AEC exhibits generally a very limited proliferation profile and is therefore not suitable for passaging. Thus, a new preparation of cells has to be used for each data set, which drives the costs up tremendously, and a reliable normalisation scheme of data observed from each set of cell preparations is needed. 

When the gas or vapor feed stream contains a component that is highly soluble in the polymer membrane and causes plasticization, then the selectivity as defined by Equation 4.6 will depend on the partial pressure or the amount of the plasticizing component sorbed into the membrane. Furthermore, pure-gas permeation measurements are generally not a good indicator of the separation performance, and mixed-gas permeation measurements will be needed [21-23]. Often, the mixed-gas selectivity is less than predicted from pure-gas measurements [8] however, the opposite has been observed [24], Competitive sorption effects can also compromise the prediction of mixed-gas behavior from pure-gas measurements [25], For gas pairs where each component is less condensable than C02, like 02/N2, it is generally safe to conclude that the selectivity characteristics can be accurately judged from pure-gas permeabilities at all reasonable pressures. When the gas pair involves a component more condensable than C02, plasticization is likely to be a factor and pure-gas data may not adequately reflect mixed-gas selectivity. When C02 is a component, the situation depends on the partial pressures and the nature of the polymer. 

Numerous experimental data on dielectric permeability e and dielectric losses tg 6 of oligomeric foams at various frequencies have been collected. For all plastic foams the foBowing linear relationship exists between e and 7 (Fig. 17) ... 

A comparison of the DCS value estimated using in silica, HTS and rat in situ perfusion estimated for a given subset of clinical candidates is given in Table 1 based on internal historical data. As indicated, in silica data predicted DCS class correctly in 74% of cases and HTS data in 81% of cases using rat in situ perfusion as the reference data set. In many cases, errors were associated with the misclassification of DCS Class I or III with class II or IV (permeability errors). Misclassifications based on solubility errors were less common. Also some very poorly soluble Class II compounds can masquerade as Class IV candidates based on precipitation and adsorption to the hlters and plastics associated with the permeability apparatus. 

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