Ethylene vinyl alcohol, packaging applications

Extrusion. Sheet, film, and profiled articles are made by extrusion (20). The resin is melted and forced through a die plate or head. Variations include multilayer and blown film applications. In multilayer coextrusions, different combinations of plastics are separately but concurrently extruded to form layered sheet or film. In the packaging industry, specialty resins such as high barrier ethylene—vinyl alcohol copolymers are combined with heat- and impact-resistant thermoplastics for food packages. The properties of each resin layer are additive, as opposed to the "averaging of property" in blends. Multilayers are also used for blow-molded containers, films, and sheet products (see also Film AND sheeting materials). 

Ethylene vinyl alcohol is also used in production of plastic bottles, thermoform film and sheet, and flexible squeeze tubes. It is being experimented with for microwave food packaging applications, but this use is not yet commercial. It could, however, provide a large new market for EVOH if the application can be successfully demonstrated. 

The major plastic resins used in packaging are high-density polyethylene, low-density and Unear low-density polyethylene, polyethylene terephthalate, polypropylene, polystyrene, and polyvinyl chloride. A variety of plastics are used in lesser quantities nylons or polyamides, polycarbonate, polyethylene naphthalate, polyvinyhdene chloride, ethylene vinyl alcohol, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, and more. In many applications, copolymers... 

In order to tap the commercial applications of LCP in packaging, processing must achieve efficient use of the high-performance polymer. There are many high value polymers and other materials that are used in thin layers. A prime example is ethylene vinyl alcohol (EVOH), a super barrier material used as a thin layer in coextruded film and multilayer containers such as ketchup bottles. Other examples are coatings, such as metal, glass, and polymeric coatings. LCP used in thin multilayer constructions should compete well with these other materials. 

Similar encouraging results have been reported by Moore and Williams [55] who led a round-robin series of tests using, for example, a five-layer structure which formed a polypropylene/tie-layer/poly(ethylene vinyl alcohol)/tie-layer/polypropylene laminate approximately 120 xm thick, as used widely in packaging applications. They also reported that a characteristic value of the adhesive fracture energy, Gg, independent of the peel angle, 0, was obtained. 

In packaging applications, polymers with barrier properties towards oxygen are used. These polymers include copolymers from ethylene vinyl alcohol, poly(acrylonitrile), or related copolymers, poly(vinyl-idene chloride), PET, or poly(ethylene naphthalate). 

Overall Brunner et al. [135] have shown that a number of polymers (poly(urethane) (PU), poly(methyl-methacrylate) (PMMA), poly(dimethylsiloxane) (PDMS) and ethylene-vinyl alcohol copolymer (EVOH)) can replace glass as packaging material for hybrid nanodevices integrating kinesin motors and microtubules, but that special care has to be taken when intense illumination is needed, for example, for fluorescence imaging. Prolonging the lifetime of biomolecules in their functional states is critical for many applications where biomolecules are integrated into synthetic materials or devices. A simplified molecular shuttle system, which consists... 

ETHYLENE-VINYL ALCOHOL COPOLYMERS AND THEIR APPLICATIONS IN FOOD PACKAGING... 

The polymers are of interest as water-soluble packaging films for a wide variety of domestic and industrial materials. (Additional advantages of the poly(ethylene oxide)s are that they remain dry to the feel at high humidities and may be heat sealed.) The materials are also of use in a number of solution application such as textile sizes and thickening agents. As a water-soluble film they are competitive with poly(vinyl alcohol) whereas in their solution applications they meet competition from many longer established natural and synthetic water-soluble polymers. 

EVOH is a copol)nner of ethylene and vinyl alcohol, obtained from ethylene and vinyl acetate, followed by hydrolysis. It is used as an oxygen barrier film in multilayer films for packaging. Its high cost limits its applications as a biodegradable material. 

Among oxygen-sensitive food-packaging applications, several materials have been developed that provide a high-barrier to gas diffusion unfortunately, however, some of these are easily plasticized by moisture and consequently are more often blended with hydrophobic polymers. The water sorption and diffusion properties of poly(ethylene-co-vinyl alcohol) (EVA) and its polypropylene (PP) blends of increasing EVA content are, therefore, of considerable interest from both fundamental and practical points of view [25]. 

In order to meet the military performance specification, a foil laminate structure is currently used in the MRE food pouch. However, current research is investigating alternative multilayer polymeric packaging structures. [4, 5] Ethylene co-vinyl alcohol (EVOH) is one polymer that is being researched. EVOH is a crystalline, random copolymer of ethylene and vinyl alcohol. EVOH is known to be a superior barrier to oxygen however the barrier properties of EVOH diminish as the humidity increases. Also, the hydrophilic nature of the material becomes a problem with retort packaging applications because the process requires water and steam for sterilization. EVOH resins absorb moisture as a function of humidity and temperature, decreasing the barrier properties of the resin during the retort process. 

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