Oxygen permeability, coating

By determining the water vapour and oxygen permeability of the free films as well as the water solubility in the coatings, the coefficients of diffusion of water could be established. 

P. H. List, G. Kaosio, Water vapor and oxygen permeability of various tablet coatings, Acta Pharm Techn 28(1) 1982. 

The vanadium pentoxide cataKtic membrane reactor was prepared by coating its sol inside the Vycor tube membrane. After heat treatment of the prepared membrane, the [010] planes of vanadium pentoxide layer were grown largely which contributes to partial oxidation reaction of 1-butene to maleic anhydride. The partial oxidation of 1-butene to maleic anhydride was carried out in the catalytic membrane reactor. The maximum selectivity of 95% was obtained at 350 °C when the surface velocity was 500cm/h. And at this condition, oxygen permeability was almost four times higher than the reaction had not occured. 

Hydrolyzed ethylene—vinyl acetate copolymers [24937-78-8]> commonly known as ethylene—vinyl alcohol (EVOH) copolymers [25067-34-9], are usually used as extrusion resins, although some may be used in solvent-coating applications. As the ethylene fraction of these semicrystalline copolymers increases, the melting temperature decreases, the permeabilities increase, and the sensitivity to humidity decreases. The permeabilities as a function of polymer composition and humidity are shown in Figure 2. Vinyl alcohol homopolymer [9002-89-5] has a very low oxygen permeability in dry conditions however, the polymer is water-soluble. Trade names for these barrier polymers include Eval, Soamol, Selar OH, and Qarene. Table 6 lists the compositions... 

Clay nanocomposites are also being developed as barrier coatings for film and for containers. The nanocomposite is deposited on the film from a solution of PVOH/ EVOH copolymer in a mix of water and isopropyl alcohol which has been used in a supersonic dispersion system to nano-disperse 7 nm diameter silica and titanium dioxide particles. The ratio of polymer to silica depends on the barrier properties required. Typical microgravure equipment can be used to coat the solution onto a plastic substrate. The result reportedly is a transparent barrier coating which is superior to silica- and alumina-coated films, and is comparable to aluminum-coated materials. Oxygen permeability at a coating thickness of 2 pm is less than 1 cc/m d atm, and moisture permeation less than f g/m d. Costs are reported to be competitive with ceramic coatings [4]. 

Oxygen Permeability of Edible Films and Coatings Compared to Common Plastic Films... 

The oxygen permeability in general decreases by 50 percent in polyamide matrix on nano-clay incorporation. Clay-polyamide nanocomposites can be used for packaging of processed meats, cheese, confectionery, cereals and boil-in-the-bag foods also for extrusion-coating applications in association with paperboard for fruit juice and dairy products, together with co-extrusion processes for the manufacture of beer and carbonated drink bottles (www.tifac.org). The nanocomposite packaging enhances the shelf life of many types of food. 

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