Ethylene Vinyl Alcohol EVOH

Ethylene vinyl alcohol (EVOH) is similar to EVA in that it is a copolymer of polyethylene with some percentage of the vinyl comonomer along the chain. In fact, EVOH is synthesized by converting VA units along a chain into vinyl alcohol (VOH) units. Grades of EVOH can be purchased with either fully or partially converted VA units to provide a wide property set. Like EVA, EVOH is primarily used in layers of coextruded film structures. 

EVOH has some important commercial properties. Perhaps the most important property is its resistance to oxygen permeation. For this reason, it is used as a barrier layer in multilayer food-grade films. Another important property of EVOH is that it is water-soluble. Therefore, it is used in applications such as the delivery of laundry detergent via dissolving packaging. 

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

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. 

Ethylene-vinyl alcohol (EVOH), 18 49, 50 Ethylene-vinyl alcohol copolymers composition of commercial barrier, 3 385t... 

ISO 14663-1 1999 Plastics - Ethylene/vinyl alcohol (EVOH) copolymer moulding and extrusion materials - Part 1 Designation system and basis for specifications... 

When an EVA copolymer is saponified, ethylene vinyl alcohol (EVOH) units are introduced (17,18). EVOH copolymers are excellent in melt moldability, gas barrier properties, oil resistance, antistatic property and mechanical strength, and are used as various types of packages in the form of a film, a sheet, a container, etc. 

Hydrolyzed ethylene-vinyl acetate copolymers, commonly known as ethylene-vinyl alcohol (EVOH) copolymers, are usually used as extmsion resins, although some may be used in solvent-coating applications. 

Perhaps the most exciting developments are yet to feature in fruit juice packaging. PET can be laminated with other plastics, such as nylon and ethylene vinyl alcohol (EVOH), to give extremely good barrier properties, and polyethylene naphthalate (PEN) may enable production of a plastic bottle that can be pasteurised at high temperatures. 

BMs commonly include from two to seven layers, although more are also used. The construction usually includes one or more barrier layers. These are plastics with a particular resistance to the transmission of water vapor or gases such as oxygen or carbon dioxide. Examples are ethylene vinyl alcohol (EVOH), nylons, and polyvinylidene chloride (PVDC). Their presence greatly enhances the performance of the BM as a package for foodstuffs, beverages, and other critical products. The barrier materials are all deficient in some respect such as price, mechanical strength, and moisture resistance. Thus not used as a material of sole construction for BM. Their use is in thin layers shielded by other more robust and economical body plastics. 

The same laminate system was used by all laboratories, namely a laminar structure with five layers based on polypropylene (PP), an adhesive, an ethylene vinyl alcohol (EVOH) layer another adhesive and another polypropylene layer. This is designated PP/adh/EVOH/adh/PP and was used in both fixed arm peel tests and T-peel tests. Peel specimen were 15 mm in width and a notional 100 mm in length. The peel arms were PP/adh (with a thickness of 51pm) and EVOH/adh/PP (with a thickness of 75pm). Although there is no rigorous value for modulus for such multi-layered arms, we have obtained a tensile modulus value for each arm and assumed the materials of the arms to be uniform for the purposes of our calculations. 

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... 

Ethylene vinyl alcohol (EVOH, trade name—Eval)... 

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. 

Different polymeric materials with high aroma and flavor barrier properties are currently being tested. Recently, it was reported that ethylene vinyl alcohol (EVOH) coextruded containers resulted in no loss of essential oil and 24% loss of vitamin C in orange juice... 

Oxygen permeability was analysed by Mocon OX-Tran2/20 (USA) using standard method (ASTM 3985). The analysis were performed in the RH range of 50 to 90% and at 20°C. Commercial synthetic films, polyamide (PA) from Biaxis Oy and ethylene vinyl alcohol (EVOH) from Akerlund Rausing Oy (Finland), were used as the reference materials. 

Ethylene vinyl alcohol (EVOH) is used to produce barrier resins impervious to most gases. This property makes the material especially useful for food packaging. EVOH resins however are sensitive to moisture. As humidity increases the permeability of vapor and odor also increases. Therefore, EVOH is coextruded with other polymers such as nylon or polypropylene to minimize this problem. 

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