Permeability to oxygen

Features Barrier properties Product form Bottles 

Fluorinated bottles do not provide any improvement in oxygen barrier over untreated straight HOPE bottles. Ei 

Penetrant cyclohexanone chlorobenzene hexane butyl alcohol trichloroethene methyl salicylate tetrahydrofuran 

Penetrant ethyl acetate isopropyl acetate acetone butyl acetate toluene xylene methyl isobutyl ketone methyl ethyl ketone 

Penetrant kerosene d-limonene motor oils pine oil diesel fuel conditioner gas additive 

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Gas Permeability. Crystalline PMP is relatively highly permeable to various organic and inorganic gases. Permeabilities to oxygen, nitrogen. 

The diffusion of oxygen through polymer films has been examined by a number of workers. Guruviah measured the permeability to oxygen of films cast from five paints (Tabic 14.4) and compared the results with the... 

The primary function of a coating is to act as a barrier which isolates the underlying metal from the environment, and in certain circumstances such as an impervious continuous vitreous enamel on steel, this could be regarded as thermodynamic control. However, whereas a thick bituminous coating will act in the same way as n vitreous enamel, paint coatings are normally permeable to oxygen and water and in the case of an inhibitive primer (red lead, zinc chromate) anodic control will be significant, whilst the converse applies to a zinc-rich primer that will provide cathodic control to the substrate. 

Chemical Resistance. Alumina is resistant to oxidation and has extremely low permeability to oxygen. It is not attacked by most chemical reagents at room temperature. 

Other optodes have been developed and tested in-vivo, all of them using a fluorophore, the fluorescence of which is quenched by oxygen. In the intravascular sensor developed by CDI, previously described, a specially synthesised fluorophore, a modified decacyclene ( Lexc=385 nm, em=515 nm), is combined with a second reference-fluorophore that is insensitive to oxygen, and is incorporated into a hydrophobic silicon membrane that is permeable to oxygen. 

It is well known that dense ceramic membranes made of the mixture of ionic and electron conductors are permeable to oxygen at elevated temperatures. For example, perovskite-type oxides (e.g., La-Sr-Fe-Co, Sr-Fe-Co, and Ba-Sr-Co-Fe-based mixed oxide systems) are good oxygen-permeable ceramics. Figure 2.11 depicts a conceptual design of an oxygen membrane reactor equipped with an OPM. A detail of the ceramic membrane wall... 

The dissolved oxygen content of a solution can be determined by measuring the diffusion current that results at a selected voltage. The Clark electrode was developed for this purpose and various modifications have subsequently been introduced. It consists basically of a platinum electrode separated from the sample by a membrane which is permeable to oxygen, e.g. Teflon or polyethylene. A reference electrode of silver/silver chloride in potassium chloride is used to complete the system (Figure 4.21). When a voltage that is sufficient to give the... 

An elecrochemical device for detecting dissolved oxygen content. The well known Clark electrode consists of a platinum wire tip surrounded by a thin film of electrolyte solution that is shrouded by a plastic membrane. The membrane is permeable to oxygen, but impermeable to... 

Soft contact lenses incorporating fluorinated polymers (F-polyether dimethacrylates, fluorosiloxanes) and showing increased permeability to oxygen and... 

Oxidation is also dependent on the permeability of the polymer to oxygen. Table 10.1 lists the permeabilities of selected polymers to oxygen. Because bulk oxidations are dependent on the permeability to oxygen, crystalline polymer forms are more resistant to oxidation than amorphous forms. Also, the very nature of the molecules present in the chains affects the tendencies toward oxidation. Thus the fluorine atom in polytetrafluoroethylene (ptfe)... 

The copolymer of isobutylene with a few percent isoprenc (butyl rubber) can be cured to produce an ozone-resistant elastomer with low permeability to oxygen and nitrogen. Butyl rubber has a Tt of — 70 C a refractive index of 1.5081, and a coefficient of linear expansion of 5.7 X 10 cm/cxn C. Chloro and bromo butyl rubber are more resistant to the permeation of oxygen and nitrogen than butyl rubber. 

Special electrochemical sensors that operate on the principle of the voltammetric cell have been developed to measure substrates such as oxygen and glucose. In the Clark oxygen sensor, a 1.5 V potential difference is applied between a silver anode and a platinum cathode which are both in contact with a KCl solution separated from the sample by a membrane permeable to oxygen (Fig. 19.6). 

Unfortunately, if a peristaltic pump is employed, then sheathing the tubes in the pump is not possible these are normally of silicone rubber, which is exceptionally permeable to oxygen. Where deoxygenation is necessary, the peristaltic pump is arranged to suck the solution and the cell is placed as close to the reservoir as possible. A note of caution is that, in this conformation, air can enter the solution relatively easily so that junctions must be well sealed. The arrangement of the flow systems is very similar to that employed in flow-injection analysis [135, 136]. 

In the area of gas permeability, the loss- crystallinity of a typical ionomer I —. IDT) results in relatively high permeability to oxygen. For packaging of fresh meat this is advantageous, but in other packaging areas, combination with a barrier layer may be required. 

The recent trend towards polyethylene terephthalate (PET) packaging presents its own problems. Typically PET containers cannot be hot filled around 50°C is the upper temperature, although some recent types can be heated to 85°C. They are also permeable to oxygen (Rodriguez el al., 1992), which allows the growth of aerobic spoilage agents. 

In addition, one may consider the addition of an antioxidant since soft gelatin capsule shell is permeable to oxygen, resulting in oxidation of oxygen-sensitive, active drug substance. However,... 

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