EVOH-copolymers

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

Table 14.2 Typical properties of EVOH copolymers (For purposes of comparison the grades seleeted all have a MFI (2.16kg, 190 C) of 1.7-1.8. Grades with other MFI values are also available)...

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. 

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. 

Bastioli et al.172 claimed expanded articles from extruded compositions of starch, mixtures of EAA and EVOH copolymers, and an inorganic carbonate. Typically, the synthetic copolymers comprised 20-40% of the composition. Preferred extrusion temperatures were in the range 180°C to 210°C. Extrusion of a typical blend in a single-screw extruder at a temperature of 180°C produced a closed cell foam with a density of approximately 1.2 lb/ft3 (19kg/m3). 

Oxygen barrier data for pure H40 systems and H40 network systems measured at RT and 0 and 50%RH are summarized in Table 1 which also reports Tg s and densities in the dry state. Due to the high concentration of hydroxyl functional groups in the periphery, excellent gas barrier characteristics for pure H40 are predicted. As seen in Table 1, the pure H40 at 0%RH displayed considerably better oxygen barrier characteristics than PET and comparable to those for EVOH with 48% (mol/mol) of ethylene. EVOH copolymers with low and moderate ethylene content are considered benchmark materials for packaging applications. When exposed to ambient humidity (50% RH) the barrier properties were reduced, but still better than PET. Figure 6 (a), (b), and... 

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... 

Besides the coextruded laminate structure in Fig. 4b, cases c-f are also viable structures for some applications. Chapter 11(47) discusses the addition of inorganic fillers to EVOH copolymer to achieve large increases in barrier properties in some applications. The effects of different loadings of mica flake in several polymers other than EVOH was also recently reported to be effective (80). 

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. 

Figure 15. Heats of Solution for Esters in an EVOH Copolymer Film...

Clay nanocomposites are also being developed as barrier coatings for film and for containers. The nanocomposite is deposited on the film from a solution of PVOH/ EVOH copolymer in a mix of water and isopropyl alcohol which has been used in a supersonic dispersion system to nano-disperse 7 nm diameter silica and titanium dioxide particles. The ratio of polymer to silica depends on the barrier properties required. Typical microgravure equipment can be used to coat the solution onto a plastic substrate. The result reportedly is a transparent barrier coating which is superior to silica- and alumina-coated films, and is comparable to aluminum-coated materials. Oxygen permeability at a coating thickness of 2 pm is less than 1 cc/m d atm, and moisture permeation less than f g/m d. Costs are reported to be competitive with ceramic coatings [4]. 

In addition, PA6 is a well-established plastic in barrier packaging, providing a barrier to oxygen and aromas as well as to microbials, and is used in food and medical packaging applications. New generation PA6 films with silicate nanoparticles with improved barrier properties are introduced to compete with the conventional barrier EVOH copolymer films. 

We note also that the reduction parameters P, V, and 7 follow to a good approximation second-order equations in copolymer composition. Quantity y changes only slightly for EVOH copolymers, from around 0.85 for PE to 0.90 for PVAl. It stays approximately constant for the other copolymers. A pronounced decrease of the ratio... 

FIGURE 8.14 Compressibility factor FEj/RF versus P/T at T= 493 K for SAN and EVOH copolymers the solid curve was calculated with the S-S equation of state for SAN copolymers. It follows the linear regression curve through aU data points. 

FIGURE 8.15 Fraction of sites occupied versus 1/V atT= 493 K for SAN and EVOH copolymers. The solid curve is the linear regression curve through the data points in the range of low reduced pressure. The linear range of y as a function of 1/V corresponds to the pressure range from normal pressure up to around 100 MPa. 

In conclusion, the compressibility factor for SAN and EVOH copolymers obeys the principle of corresponding states over a wide range of pressure. Deviations are observed only for PS at P > 120MPa (outside the scale in Figure 8.14). Also, the fraction of occupied sites follows a master curve in the range of low reduced pressure. It varies linearly with inverse reduced volume. At high pressures, the quantity y deviates from linearity and approaches unity. Concomitantly, the free volume reduces with increasing pressure. At P odd x/roo n,o. -otir, in-4... 

Here we test Eq. (8.30) for random copolymers by plotting surface tension versus pIk) I (Figure 8.17). The linear regression curve (correlation 0.9999) results for EVOH copolymers. It has the slope... 

K were taken from Table 8.2. The dashed regression line was calculated using data of EVOH copolymers. It has a slope given by Eq. (8.32). The inset shows data of EVAc on an enlarged scale. , EVOH (220°C) A, SAN (220 C) o EVAc (160°C). 

FIGURE 8.19 yAJRT versus reduced temperature for EVOH copolymers at P = 0. 

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