Permeability coefficients values

Example 9-3. A 20 cm long HDPE tube with an external diameter of 10 cm and a wall thickness of 1 mm is filled with an oxygen absorbing substance. Both ends of the pipe are sealed with a 100 pm thick LDPE film and the tube is stored in air. What is the total oxygen permeation into this tube using the permeability coefficient values from Table 9-2 for HDPE and LDPE at 25 °C ... 

When the ends of the HDPE tube are sealed with 10 pm PVDC film one gets the permeation, using permeability coefficient value for oxygen through PVDC at 30°C given in Table 9-2, in the following way ... 

The total permeation of the pouch is calculated using Eq. (9-16). Using the permeability coefficient values for the different materials from Table 9-2 one gets ... 

Example 9-10. Estimate the average value for the diffusion coefficient for oxygen and carbon dioxide in polypropylene with 50% degree of crystallinity at 30 °C. Use the corresponding molecule diameter o and the average Tg value of 267 K for PP. Calculate the corresponding permeability coefficient value using the solubility coefficient value determined in Example 9. 

Table A1 lists and Figure 15.1 shows 144 permeability coefficient values for 83 eompounds (83 fully validated and 61 excluded data points 45 fully validated compounds) measured in hairless mouse skin. All of the measurements excluded from this database were more than 90% ionized. Etorphine is distinguished on this figure because Vecchia and Bunge (2002b) used the fact that the human permeability coefficient is larger than the hairless mouse permeability coefficient to support exclusion of the measurement from the fully validated database for human skin. Notice that the hairless mouse permeability coefficient of etorphine is consistent with measurements for other cations, which was not the case with the human permeability coefficient for etorphine (Vecchia and Bimge, 2002b).

There are fewer extremely low (i.e., logP < -4.0) permeability coefficient values in hairless mouse skin than in human skin. 

The largest permeability coefficient values are similar in both species (-0.7 < log Pc <-0.9). 

Table A2 tabulates and Figure 15.2 shows 41 permeability coefficient values of 33 different compounds (18 fully validated and 23 excluded data points 14 fully validated compounds) measured in hairless rat skin. The database contains permeability coefficients for structurally diverse compounds, predominantly pharmaceutically active compounds, with varied chemical properties. Vinpocetine was excluded because (1) the concentration was not reported, and as a result the fraction unionized could not be determined and (2) could not be reliably calculated (vinpocetine has structural fragments that are not adequately represented in Daylight software PCModels, 1995). Vinpocetine is plotted at the calcidated value for log...

Table A3 tabulates and Figure 15.3 shows 17 permeability coefficient values for 11 compoimds (14 fully validated and 3 excluded data points 10 fully validated compoimds) measured in rat skin. This database is small and consists mainly of phenols, alcohols, and water. Because all chemicals in this database are of relatively low MW and many are structurally related (meaning that MW and log are correlated), log is more clearly linear with log than in Figure 15.1 and Figure 15.2. Water permeability coefficients are similar to human skin (i.e., 1.47 x 10" cm h" in rats compared to 1.18 x 10" cm h in humans). However, the permeability coefficient for paraquat in the rat is significantly higher than in humans (i.e., 3.07 X 10" cm h in rats compared to 8.70 x lO- cm h" in humans, a ratio of about 35). Paraquat permeability was similar in the haired and hairless rat.

Table A4 lists and Figure 15.4 shows 37 permeability coefficient values for 28 compounds (31 fully validated and 6 excluded data points 28 fully validated compounds) measured in shed snake skin. Although the database is small, it is diverse and consists of compounds, predominantly pharmaceutically active compounds, spanning a wide range of molecular structures and properties. These permeability...

Dermal absorption in different animal species has many qualitative similarities to dermal absorption in humans that can be observed through examination of permeability coefficients. However, for the purpose of estimating dermal absorption in humans, the large numbers of permeability coefficient values determined in animal skins are of limited use until quantitative relationships to human skin are established. Based on the data collected so far, we have developed regression equations of permeability coefficients as functions of log and MW for several animal species (hairless mouse, hairless rat, rat, and snake). The regression equation from hairless mouse skin is similar to an equation of the same form for human skin. On average, hairless mouse skin is 3.1 times more permeable than human skin this ratio appears to be independent of but may increase weakly for higher MW compounds. 

Permeability coefficient values for water, mannitol, and paraquat were digihzed from Figure 4. The discrepaney in values shown in Figure 4 and Table 1 appear to be an error in the typesetdng of Table 1. We were unsuecessM at contacting the authors. 

The permeability coefficient, P, combines the effects of the diffusion and solubility coefficients. The barrier characteristics of a polymer are commonly associated with its permeability coefficient values. The well-known relationship P = DS holds when D is concentration independent and S follows Henry s law. Standard methods for measuring the permeability of organic compounds are not yet available. ASTM E96 describes a method for measuring the water vapor transmission rate. ASTM D1434 describes a method for the determination of oxygen permeability. 

As indicated, a material that is a good barrier has a low value of the combined diffusion coefficient and solubility coefficient values for a particular penetrant. Preferably, both D and S should be low. For instance, polyethylene is an excellent barrier to water because water has very low solubility and diffusion coefficient values in polyethylene, but it has a relatively high P for oxygen because O2 has higher solubility than water. A permeability coefficient value is valid only for a particular polymer/permeant pair, and as in the case of polyethylene, a structure may be a good barrier for a certain permeant and only a fair or poor barrier for a different one. 

The gas transport properties of the PI-POSS composite membranes were measured at 35 °C at an applied upstream pressure of 3.5 atm. Table 6.2 lists the permeability coefficient (P) and permselectivity data for the CO2-CH4 and O2-N2 gas pairs for the four structurally different PI-POSS composite membranes. The diffusion coefficients were calculated from the time-lag value of gas flow versus time plot. For better understanding, the permeability coefficient values for each gas through the pristine PI membranes (without POSS) are also presented along with their selectivity for CO2-CH4 and O2-N2 gas pairs, given in parentheses (Table 6.2.)... 

The order of permeability coefficient for the four gases through these PI-POSS hybrid membranes was P (CO2) > P (O2) > P (N2) > P (CH4), which follows the same order as their kinetic diameter (A) CO2, 3.3 O2, 3.46 N2, 3.64 CH4, 3.8 [109]. Compared with the pure PI membranes, a significant increase in permeability coefficient values was observed for all of the PI-POSS hybrid membranes, whereas the selectivity was comparable for different gas pairs. The higher permeability coefficients for the hybrid membranes were attributed to the presence of bulky porous POSS cages... 

Table 2 presents the CO2 permeability coefficient values as a function of temperature in the range of 25-45°C at 0% RH. The activation energy was calculated according to the Arrhenius equation (25). 

Solubility coefficient values are of great use in predicting permeant-polymer compatibility however, for packaging applications permeability coefficient values better describe the quality of the barrier of a material, and are more useful in calculating the shelf life of a product. Fig. 6b compares the ethyl acetate permeabihty coefficient values of PLA, LDPE [49], PP [50], and PET [51]. Ethyl acetate permeability coefficients in PLA are lower than those for PP and LDPE and slightly higher than those for PET. RST cannot be used to predict permeability coefficients since it helps only to obtain the relation between solubility and AS, which is not enough to predict permeability and also depends on the diffusion coefficient. 

Permeability coefficient values (29) for various actinides in flat sheet SLM (Celgard 2500) and hollow-fiber module (Accurel ) configurations are presented in Table 4. For the experiments conducted with synthetic nuclear waste solutions... 

The oxygen permeation testing of compression-molded plain PMMA film with 0.25 mm thickness was conducted, and the permeability coefficient was found to be 1338.86 X 10 mol/m s Pa. This value is comparatively much higher than the permeability coefficient values for sandwich films with PMMA—GO nanofiber elec-trospun core, as summarized in Table 8.18. 

Clays are believed to increase the barrier properties by creating a maze or tortuous path that retards the progress of the gas molecules through the matrix resin. The direct benefit of the formation of such a path is clearly observed in near to exfoliated PLA/OMSFM nanoeomposites. The relative permeability coefficient value, i.e. Ppcn/Pp, where Ppcn and Pp are the nanocomposite and pure polymer permeabiUly coefficient, respectively, was plotted as a function of the wt.% of OMSFM in Fig. 3.12. The data were analyzed with the Nielsen theoretical expression (see below), allowing prediction of gas permeability as a function of the length ( ls) and thickness of filler particles (Als), as well as their volume fraction ( s) in the PLA-matrix. 

---