Oxygen permeation effect

Therefore, assnming an effective area size as S and a membrane thickness as L, respectively, the total jonle heat value caused by oxygen permeation can be derive as ... 

Fig. 10.5. The effect of sample thickness on oxygen permeation through calcia-stabilized zirconia at 1230°C. Solid lines are theoretical results calculated using Eq. (38). Reprinted fixMn Dou et al. [95J.

Long-term oxidative degradation of an ion-beam irradiated polymer was studied. Silicon oxide thin layers were deposited on the surfaces of high density polyethylene (HDPE) to suppress the oxygen permeation. HDPE samples irradiated with a C6+ ion-beam were stored up to 12 months after the irradiation and the evolution of the chemical structure was followed by micro-Fourier transform infrared (micro-FT-IR) spectroscopy. Silicon oxide layers were found effective to suppress the long-term oxidative degradation of the ion-irradiated polymer. 

The structure of an amorphous polyamide prepared from hexamethylenediamine and isophthalic/tere-phthalic acids was modified in order to determine the effect of chemical structure on the oxygen permeation properties. The greatest increase in permeation was obtained by lengthening the aliphatic chain. Placement of substituents on the polymer chain also led to increased permeation. Reversal of the amide linkage direction had no effect on the permeation properties. Free volume calculations and dielectric relaxation studies indicate that free volume is probably the dominant factor in determining the permeation properties of these polymers. 

Figure 1 shows the effect of relative humidity (RH) upon the oxygen permeation values (OPV) of a few representative polymers. This data is reported in the units of cc-mil/(100 sq.in.-day-atm). For many polymers such as polyethylene, OPV is essentially unaffected by changes in RH. 

Effect of Chain Length. The initial part of this study consisted of determining the effect of aliphatic chain length on the permeation properties of the polyamides. A series of isophthal-amides (n-I) was prepared where the aliphatic chain length was systematically altered from 2 to 10 methylenes (5). Crystalline melting points were observed by DSC for 2-1 and 1-1, so permeation data was measured only for 4-1 through 10-1. The thermal, density, and oxygen permeation data for this series are contained in Table I. 

Through systematic modification of the polymer backbone, the effects of chemical structure upon the oxygen permeation properties of aliphatic-aromatic amorphous polyamides were determined. In this class of polymers, the greatest effects were obtained by alteration of the chain length and disruption of the amide hydrogen bonding by N-alkylation. It is remarkable that reversal of the amide linkage has no effect whatsoever on the permeation properties of the examples studied. 

Putting desiccant in a layer of multilayer containers made with the same EVOH polymer results in much less oxygen permeation. The Retort Shock and slow barrier recovery effects do not take place. Moreover, this is true even when the desiccant is separated from the EVOH by a thin polymeric layer so that the EVOH and the desiccant cannot interact chemically. Retorted containers with desiccant behave more like unretorted containers without desiccant oxygen permeation is controlled almost exclusively by the water activity of the EVOH layer. Morphological changes in the EVOH layer after retorting appear to be very small when desiccant is present. We attribute this to rapid transport of excess moisture from the EVOH to the desiccant which results in healing the... 

Figure 1 shows the oxygen permeation values for a series of blends of aluminum, mica and talc in an EVOH resin containing 44 mole % ethylene. The relative effectiveness of the three fillers are proportional to their aspect ratios as predicted by theory. 

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