Alcohol ethylene vinyl

EVOH resins were introduced commercially in 1970 in Japan, and their use has expanded rapidly, especially where an excellent oxygen barrier is required. Formulations currently in use typically contain 27 to 48 mole % ethylene. The lower the amount of ethylene, the better is the barrier, when the polymer is dry. The lower the percentage of ethylene, the greater is the moisture sensitivity, and the difficulty 

EVOH can be extruded in films, blow molded, or injection molded. It can also be processed by coextrusion or lamination, in combination with PE, PP, PET, nylons, and other resins. Applications in packaging include flexible structures and rigid containers, as shown in Table 4.12. Typical applications are ketchup and barbecue sauce bottles jelly, preserves, vegetable juice, and mayonnaise containers and meat packages. Nonfood applications include packaging of solvents and chemicals. 

Processing method Sample application Sample structure 

Cast coextrusion Processed meats, cheese PET/EVOH/EVA 

Blown coextrusion Red meat LLDPE/EVOH/LLDPE 

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HDPE, high density polyethylene PP, polypropylene EVA, ethylene—vinyl alcohol SMC, sheet-molding compound ERP, fiber-reinforced plastic LDPE, low density polyethylene PE, polyethylene BMC, bulk mol ding compound TPE, thermoplastic elastomer. 

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. 

The properties of these new materials are being studied. Hydroboration is also appHed for the conversion of double bonds in polymers into hydroxyl groups (450—454). Well-defined copolymers of ethylene—vinyl alcohol can be prepared (455). 

Fig. 2. Oxygen permeabilities of ethylene—vinyl alcohol copolymers at 20°C (10). See Table 1 for unit conversions.

Table 6. Composition of Ethylene Vinyl Alcohol (EVOH) Copolymers...

Values for vinyUdene chloride copolymer and ethylene—vinyl alcohol are extrapolated from higher temperatures. 

Permeation in the vinyUdene chloride copolymer and the polyolefins is not affected by humidity the permeability and diffusion coefficient in the ethylene—vinyl alcohol copolymer can be as much as 1000 times greater with high humidity (14—17). 

In addition to the above materials a number of copolymers containing vinyl acetate have been marketed. Ethylene-vinyl acetate (EVA) copolymers are discussed in Chapter 11 and vinyl chloride-vinyl acetate copolymers in Chapter 12. On the other hand, the commercial ethylene-vinyl alcohol copolymers, although derived from EVA, are considered briefly in this chapter since in weight terms the ethylene component is usually the minor one. 

Of commercial barrier polymers, only the ethylene-vinyl alcohol (EVOH) copolymers (see Chapter 14) show greater resistemce to gas permeability. However, the EVOH materials exhibit much higher levels of moisture absorption. 

EVOH, EVAL, EVOL Ethylene-vinyl alcohol ... 

By designing the repeat unit into the parent diene (containing either an alkyl branch or functionality), only a single type of repeat unit is formed upon polymerization, giving pure polymer microstructures. To date, perfectly controlled ADMET ethylene copolymers have included ethylene-CO,34 ethylene-vinyl alcohol,35 ethylene-vinyl acetate,36 and ethylene-propylene.20 Figure 8.12... 

EVAL Ethylene-vinyl alcohol copolymer, PA6/6.6 Polyamide 6/6.6... 

HB Hopfenberg, A Apicella, DE Saleeby. Factors affecting water sorption in and solute release from glassy ethylene-vinyl alcohol copolymers. J Membrane Sci 8 273-281, 1981. 

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