Oxygen-permeating polymers

The conventional PSP consists of sensor probe molecules contained in a transparent oxygen-permeable polymer film matrix (Fig. 3). The oxygen molecules permeate into the polymer film matrix by diffusion. In contrast, PSP consists of sensor molecules directly adsorbed onto a substrate such as an anodic oxidized aluminum plate (Fig. 4). Thus, polymers and probes are important factors for PSP application. 

Extensively studied is oxygen permeation through dense ceramic membranes (e.g. perovskhes). Temperatures > 600 °C are applied. Here, oxygen splits at the surface and is transited as 0 . Porous membranes include porous polymer films (cellulosics, polyamides) as well as amorphous inorganic materials (alumina, silica). 

The most common rubber polymers used in SVI closures are natural and butyl rubber (Table 9). Silicone and neoprene also are used but less frequently in sterile products. Butyl rubber has great advantages over natural rubber in that butyl rubber requires fewer additives, has low water vapor permeation properties, and has good characteristics with respect to gaseous (e.g., oxygen) permeation and reactivity with the active ingredient. 

Film Forming and Selective Oxygen Permeation. Selective oxygen permeation was evaluated mainly for the polymers having short ollgoslloxane side chains. Oxygen permeation constants (Pq ) 1... 

As an attempt to Improve the selectivity of oxygen permeation, copolymers with FA, and polymers of fluoroalkyl substituted S2 were synthesized. The results are also shown In Figure 5. Introduction of fluoroalkyl groups, at present, does not Improve the selectivity significant. 

If the oxygen permeation constant and the rate of oxygen consumption for the material remain relatively constant as a function of total absorbed dose, a steady state in heterogeneous oxidation will be approached. If the rate of oxygen consumption by reaction with free radicals generated by the radiation exceeds the rate of supply of oxygen from the edges of the polymer sample, distinct... 

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. 

Barrier resins, polymers which have relatively low rates of small molecule permeation, have revolutionized the packaging industry in recent years. For food packaging applications, it is specifically desirable to impede oxygen permeation. Each food type has its own particular packaging requirements, which leads to the use of many polymer classes at a variety of temperatures and relative humidities in these applications. 

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. 

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... 

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