Ethylene vinyl alcohol barrier properties

The gas barrier properties (O2, CO2 and ethylene) of protein-based materials are highly attractive since they are minimal under low RH conditions. Oxygen permeability (around 1 amol/m/s/Pa) is comparable to ethylene vinyl alcohol (EVOH) properties (0.2 amol/m/s/Pa) and much lower than the properties of LDPE (1,000 amol/m/s/Pa) [61] (Table 11.12). The O2 permeability of protein films is about 10-fold higher that EVOH-based films, mainly due to the high plasticiser content of protein-based films. 

However, the regio-random distribution of functional groups can be avoided by an acyclic diene metathesis (ADMET) polymerization technique using symmetric monomers (33). The molecular weights of these polymers are restricted to < 3 x 104 Dalton by ADMET. Due to their rich hydrocarbon content, the barrier properties in final ethylene vinyl alcohol copolymers are reduced. 

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. 

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. 

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). 

EVA-copolymers are used as sealants. With vinyl acetate contents ranging from 15-40 % these copolymers are particularly applicable for the production of hot melts because of their good compatibility with fillers and other plastics. Ethylene vinyl alcohol copolymer (EVOH) is a plastic with exceptional barrier properties. It is manufactured by saponification of EVA. 

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. 

Barrier Properties of Ethylene—Vinyl Alcohol Copolymer in Retorted Plastic Food Containers... 

TSAI WACHTEL Barrier Properties of Ethylene- Vinyl Alcohol... 

There are two polymers used in a maj ority ofhigh barrier food packages copolymers containing polyvinylidene chloride (Saran ) and ethylene-vinyl alcohol copolymer (Eval, Selar-OH ). Packages in which either polyvinylidene chloride or ethylene-vinyl alcohol copolymer (EvOH) provide the barrier are invariably multilayer since neither of these materials offers the properties required to make a good monolayer structure. There are advantages and disadvantages associated with each of these materials, and the... 

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... 

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. 

Hydrolysis of EVA copolymers yields ethylene-vinyl alcohol copolymers (EVOH). EVOH has exceptional gas barrier properties as well as oil and organic solvent resistance. The poor moisture resistance of EVOH is overcome by coating, coextrusion, and lamination with other substrates. 

In this chapter we discuss PVT and surface properties of three sets of random copolymers. Monomer units are ethylene, vinyl alcohol, and vinyl acetate, as well as styrene and acrylonitrile. Random copolymers comprising these monomers are used widely. As an example, ethylene-vinyl alcohol random copolymers (EVOHs) have excellent gas barrier properties. They are used for food-packaging films or in fuel tank liners [Takahashi et al., 1999 Alvarez et al., 2003 Ito et al., 2003 Lopez-Rubio et al., 2003 Muramatsu et al. 2003]. 

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