Barrier plastic

Aryl Phosphates. Aryl phosphates were introduced into commercial use early in the twentieth century for flammable plastics such as cellulose nitrate and later for cellulose acetate. CeUulosics are a significant area of use but are exceeded now by plastici2ed vinyls (93—95). Principal appHcations are in wire and cable insulation, coimectors, automotive interiors, vinyl moisture barriers, plastic greenhouses (Japan), furniture upholstery, conveyer belts (especially in mining), and vinyl foams. 

Sugared cereals are often packaged in aluminum foil or barrier plastic, eg, ethylene vinyl alcohol, laminations to retard water vapor and flavor transmission (see Wheat and other cereal grains). 

Thermoform able sheet may be mono- or multilayer with the latter produced by lamination or coextmsion. Multilayers are employed to incorporate high oxygen-barrier materials between stmctural or high water-vapor barrier plastics. Both ethylene vinyl alcohol copolymers and poly(vinyhdene chloride) (less often) are used as high oxygen-barrier interior layers with polystyrene or polypropylene as the stmctural layers, and polyolefin on the exterior for sealing. 

Because high oxygen-barrier plastics are incompatible with other thermoplastics, extmdable adhesives must be extmded between the layers. Scrap can be included within the multilayer stmcture, provided an extmdable adhesive is incorporated. 

Procedures to prevent contamination of clean areas (appropriate barriers, plastic sheeting, etc.)... 

With the growth of plastic use in containers and packages, requirements to make them more compatible or useful resulted in new developments occuring and continue to occur. The two major approaches for providing permeability resistance in plastic containers involve chemically modifying the plastics surfaces and, more important from a marketing standpoint, the use of barrier plastics with nonbarrier types to meet cost-to-performance requirements. This is achieved through coextrusion, coinjection, corotation, and other such processes (Chapter 8). 

Barrier plastics using oxifluorination are widely used for foods. With these, barriers are needed to protect them against spoilage from oxidation, moisture loss or gain, and changes or losses in favor, aroma, or color. Most plastics can be considered barrier types to some degree, but as barrier properties are maximized in one area (as the gases such as O2, N2, or CO2), such other properties as permeability and moisture resistance diminish. 

A similar problem is presented by vehicle tires and certain blow molded bottles, which must be virtually impermeable to air and other gases. An example of the use of a very impermeable elastomers is butyl rubber. Because of its impermeability to gases, butyl rubber is used as a roof coating. With plastic bottles, different layers of both coinjected and coextruded plastics (Chapter 8) can be used to fabricate the bottle to make it impermeable to different vapors and gases depending on the barrier plastic included. 

Barrier plastic Also called barrier layer. They are materials such as plastic films, sheets, etc. with low or no permeability to different products. 

Speas, C. A., Closure Performance Requirements for High Barrier Plastics... 

Salame M Plastic Film Technology High Barrier Plastic Films for Packaging. Tech-nomic, Lancaster, Basel... 

Another important packaging development area is plastic. Various plastics have been and continue to be used high- and low-density polyethylene (HDPE, LDPE), polyvinyl chloride (PVC), polystyrene (PS) and various barrier plastics. These can be formed into bottles of conventional shape or fed into machines producing form-fill-seal packages, typically cups. 

Of the styrene copolymers used for food packaging the styrene-acrylonitrile copolymer known as SAN still needs to be mentioned. SAN copolymers possess better mechanical properties and better resistance to oils and aroma compounds than PS. Copolymers with acrylonitrile fractions of 20-35 % find uses as household and camping dishes. Copolymers with a higher acrylonitrile content (> 60%) have earned particular importance as barrier plastics. With an increasing acrylonitrile fraction, the gas permeability decreases sharply. 

Barrier Plastics. When plastics replace metals and glass in packaging, their permeability is often a limiting property. Barrier performance generally increases with density and crystallinity. The most promising barrier plastics include ethylene/vinyl alcohol, polyvinylidene chloride, polyacrylonitrile, and polyethylene naphthoate. These are used most efficiently by laminating them to commodity plastics such as polyethylene and polyethylene terephthalate. 

Different barrier plastics meet different requirements. A very popular barrier plastic is EVOH (ethylene-vinyl alcohol copolymer) that can be tailored to the needs of packages and other products.80 Generally the thickness ranges from 0.5 to 3.0% of the wall thickness it can be thicker if higher barrier is required. Generally EVOH thickness greater than 8% of the container sidewall can lead to internal structural failures that can fail on drop tests. Also a very thick layer tends to be difficult to process consistently. The EVOH s crack resistance improves as its ethylene content increases. 

Barrier plastics, used in food and beverage packaging applications, which have high resistance to permeation of gas and flavor-aroma molecules. 

Barrier plastics will be used as examples in this paper. Barrier and selectivity are two sides of the same coin. Both properties are determined by the same types of transport phenomena. [3] Similar techniques can, therefore, also be applied to study separation membranes. The same approximations are valid if the mixture flowing through the membrane is sufficiently dilute that (i) it does not significantly affect the structure and properties of the membrane, and (ii) the components of the mixture can be treated as independent penetrants. The same general approaches can also be applied to concentrated mixtures, but only provided that certain simplifying approximations are not made. 

A study is in progress on the transport of penetrant molecules in barrier plastics, utilizing a synergistic combination of techniques. 

Marcus, S.A. andP.T. DeLassus, "Recycle and Permeation Studies on Barrier Plastics Containers", Second International Ryder Conference on Packaging Innovations, 1984, p 137. 

With the growing demand for coextruded products, barrier plastics have shown significant growth in the last several years. Historically, the high barrier resins market has been dominated by three leading materials — vinylidene chloride (VDC) copolymers, ethylene vinyl alcohol (EVOH) copolymers, and nitrile resins. Since 1985, however, there has been a lot of interest worldwide in the development of moderate to intermediate barrier resins, as apparent from the introduction of a number of such resins, notably, aromatic nylon MXD-6 from Mitsubishi Gas Chemical Company, amorphous nylons SELAR PA by Du Pont and NovamidX21 by Mitsubishi Chemical Industries, polyacrylic-imide copolymer EXL (introduced earlier as XHTA) by Rohm and Haas and copolyester B010 by Mitsui/Owens-Illinois. 

In the last few years, a rapid expansion in the use of high gas barrier plastic structures for food packaging has taken place. These structures include multilayer films, trays, bottles and cups, "bag in the box" and "bag in the barrel" type packages and laminated cartons. 

Britol . [Witco/Sonnebwn] Mineral oil USP bindo, carrier, conditioner, de-foamer, dispersant, extender, heat transfer agent, lubricant, moisture barrier, plasticizer, protective agent, and/or softener in adhesives, agric., cleaning, cosmetics, food, pl plastics, tmctiles. 

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