Ethylene-Vinyl Acetate EVA

Owing to the good barrier property, the EVA-based clay nanocomposites are used for packaging, bottle-making, etc. [168]. 

Ethylene vinyl acetate (EVA) is a copolymer of polyethylene. It is similar in chemistry to PE,but it has some percentage of vinyl acetate (VA) included along the chains (Fig. 1.8). The amount of VA that is included, generally between about 5 and 20%, depends on the desired properties of the polymer. VA adds polarity, or adhesion, to the polymer and, so, improves the compatibility of the polymer with fillers and gives the polymer adhesive properties. Most blown film applications using EVA do so as layers in coextruded products, such as food and electronics packaging. 

Ethylene vinyl acetate copolymers (EVA) are produced by copolymerizing ethylene and vinyl acetate monomers. 

EVA copolymers with vinyl acetate (VA) contents ranging from 5 to 50% are commercially available. For most food applications, VA ranging from 5 to 20% is recommended. EVA resins are mainly recognized for their flexibility, toughness, and heat sealability. 

Can be crosslinked by peroxides and/or, may also be chemically blown to give cellular products the density of crosslinked, foamed EVA can be very low indeed and is far 

Available in a wide range of grades but can be a very easy flow material MFI (MFR) can range fi-om 2 to 35. As usual, Wgher molecular weight grades have the worst flow. 

Flex cracking at low temperatures and also to ozone cracking. Disinfectants, ethylene oxide and sodium hypochlorite may be used for cleaning or disinfection. Chemical resistance is similar in many respects to LDPE but not as chemically resistant. Low MFR grades have the best resistance. 

Steam sterilization - use gamma irradiation if sterilization is required. Resistance to aromatic and chlorinated solvents is poor. Soluble in aromatic and chlorinated hydrocarbons at elevated temperatures. 

With a density of 0.926 to 0.95gcm-3 (0.537 to 0.551 oz./cu.in.) the material (solid, non-filled material) will float in both water and in saturated, magnesium chloride. The natural color of the material is similar to that of LDPE at low VA content (i.e. 

AEM is typically used because it gives an optimal balance in properties such as compression set, low-temperature flexibility, heat aging resistance, oil resistance, and excellent vibration damping. Therefore AEM is commonly preferred in automotive applications such as power steering, transmissions, and engine seals. 

Other specialty elastomers can substitute for AEM in these applications however, they may be more expensive or not have the right combination of properties. 

Tight Supply Situations in the Past and Future Supply Outlook 

Ethylene vinyl acetate, commonly referenced as EVA, is a rubberlike polymer that sometimes can be processed on either rubber or plastics processing equipment. EVA has good clarity and can be compounded with peroxide curatives and sometimes blowing agents (for foam) for use in athletic shoes (for absorbing shock), ski boots, hose, tubes, wire insulation, solar cell encapsulation, and medical applications. 

EVA is a copolymer of ethylene and vinyl acetate that is formed through vinyl 

This copolymer is really an elastoplast, with properties intermediate between that of a plastic and an elastomer. A suggested surface preparation method is as follows  

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Pentaerythritol in rosin ester form is used in hot-melt adhesive formulations, especially ethylene—vinyl acetate (EVA) copolymers, as a tackifier. Polyethers of pentaerythritol or trim ethyl ol eth an e are also used in EVA and polyurethane adhesives, which exhibit excellent bond strength and water resistance. The adhesives maybe available as EVA melts or dispersions (90,91) or as thixotropic, one-package, curable polyurethanes (92). Pentaerythritol spko ortho esters have been used in epoxy resin adhesives (93). The EVA adhesives are especially suitable for cellulose (paper, etc) bonding. 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

Ethylene vinyl acetate (EVA) polymers are used in thermoplastic and thermosetting jacketing compounds for apphcations that require flame retardancy combined with low smoke emission during the fire as well as the absence of halogen in the composition. 

Fig. 2. U.S. consumption of vinyl acetate, where represents PVAc I, poly(vinyl alcohol) (PVA) A, ethylene—vinyl acetate (EVA) O, PVB , EVOFl ...

The very low density materials (VLDPEs) introduced in the mid-1980s are generally considered as alternatives to plasticised PVC (Chapter 12) and ethylene-vinyl acetate (EVA) plastics (see Chapter 11). They have no volatile or extractable plasticisers as in plasticised PVC nor do they have the odour or moulding problems associated with EVA. Whilst VLDPE materials can match the flexibility of EVA they also have better environmental stress cracking resistance, improved toughness and a higher softening point. 

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. 

For reasons explained below, the effect of increasing the vinyl alcohol content in EVOH is quite different to that of increasing the vinyl acetate content in EVA. In the case of ethylene-vinyl acetate (EVA) copolymers, increasing the vinyl acetate content up to about 50% makes the materials less crystalline and progressively more flexible and then rubbery. In the range 40-70% vinyl acetate content the materials are amorphous and rubbery, whilst above 70% the copolymers become increasingly rigid and brittle. 

Variations in the composition of a copolymer can cause substantial differences in the properties of the copolymer. Compositional information about copolymers may be acquired using selective detectors. Figure 3.9 shows the separation of an ethylene-vinyl acetate (EVA) copolymer by FfPSEC using IR detectors. One IR detector monitors the vinyl acetate carbonyl at 5.75 /u,m, and the other IR detector monitors the total alkyl absorbance at 3.4 /cm. 

Coran and Patel [33] selected a series of TPEs based on different rubbers and thermoplastics. Three types of rubbers EPDM, ethylene vinyl acetate (EVA), and nitrile (NBR) were selected and the plastics include PP, PS, styrene acrylonitrile (SAN), and PA. It was shown that the ultimate mechanical properties such as stress at break, elongation, and the elastic recovery of these dynamically cured blends increased with the similarity of the rubber and plastic in respect to the critical surface tension for wetting and with the crystallinity of the plastic phase. Critical chain length of the rubber molecule, crystallinity of the hard phase (plastic), and the surface energy are a few of the parameters used in the analysis. Better results are obtained with a crystalline plastic material when the entanglement molecular length of the... 

Ethylene-vinyl acetate EVAs (in the polyolefin family) have exceptional barrier properties, good clarity and gloss, stress-crack resistance, low temperature toughness/retains flexibility, adhesion, resistance to UV radiation, etc. They have low resistance to heat and solvents. 

This is another important and widely used polymer. Nanocomposites have been prepared based on this rubber mostly for flame-retardancy behavior. Blends with acrylic functional polymer and maleic anhydride-grafted ethylene vinyl acetate (EVA) have also been used both with nanoclays and carbon nanotubes to prepare nanocomposites [65-69]. 

FIGURE 4.2 Transmission electron microscopic (TEM) image of ethylene-vinyl acetate (EVA)-expanded graphite (EG) (4 wt%) nanocomposites. (From George, J.J. and Bhowmick, A.K., J. Mater. Sci., 43, 702, 2008. Courtesy of Springer.)... 

A number of other polymers have the characteristics of TPE and some are available commercially, such as (1) 1,2-polybutadiene, (2) tran -polyisoprene (PI), (3) modified polyethylene (PE) (e.g., ethylene vinyl acetate [EVA] and ethylene ethyl acrylate [EEA]), (4) nonhydrocarbon elastomer-based TPEs, (5) metallocene elastomers/TPEs (MEs/TPEs), and (6) graft copolymeric TPEs. 

Ethylene-vinyl acetate Fetterman [37] reinforced compounded ethylene-vinyl acetate (EVA) copolymer by using short hbers and found that silane coupling agents were effective at establishing improved hber-matrix adhesion. Das et al. [38] prepared carbon fiber-filled conductive composites based on EVA and studied the electromagnetic interference shielding effectiveness of the composites. 

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

FIGURE 31.2 Plots of crystalline melting point, heat of fusion and percent crystallinity of ethylene-vinyl acetate (EVA) samples versus (a) radiation dose (b) trimethylolpropane trimethacrylate (TMPTMA) level from differential scanning calorimetry (DSC) studies. (From Datta, S.K., Bhowmick, A.K., Chaki, T.K., Majali, A.B., and Deshpande, R.S., Polymer, 37, 45, 1996. With permission.)... 

The two-step degradation of commercial ethylene-vinyl acetate (EVA) copolymers has been investigated using TGA coupled with FTIR detection of the pyrolytic products evolved [48]. Acetic acid was evolved from the first... 

In this example a polymer laminate film (for packaging) was examined, which was composed of nine layers (see Table 2), by both FTIR imaging and Raman line scan. For the IR measurements thin sections (5 pm) were cut. The central ethylene/vinyl acetate (EVA) copolymer layer is very soft, and holes can be seen in the visible image (Figure 12). 

Fig. 11 illustrates the smoke suppression effect of the zinc borate when used in conjunction with ATH in a halogen-free ethylene-vinyl acetate (EVA) system. Sumitomo Electric, in a... 

Ethyleneurea resins, 2 639 Ethylene-vinyl acetate (EVA) copolymers (EVAc), 7 639 9 57-58 25 582 Ethylene-vinyl acetate copolymer food packaging, 18 44... 

More recently, Harner et al. (2003) coated ethylene vinyl acetate (EVA) onto glass (polymer coated glass [POG]) for use as fugacity sensors or equilibrium samplers of SVOCs in indoor and outdoor air. The EVA film fhickness was 1.1 and 2.4 qm depending on the application and as expected, SVOC sorption capacity and times to equilibrium were shown to be directly proportional to film thickness. The clearance capacity Ey volume of sample medium cleared of chemical) of a sorbent for an analyte is given by... 

Blends of ethylene-vinyl acetate (EVA) copolymer with metallocene-catalysed elastomeric ethylene-alpha-olefin copolymer were investigated and were found to be immiscible in the melt and solid state but mechanically compatible. The morphology (SEM), thermal (DSC), rheological (viscosity), mechanical (including tensile, shear thinning and elastic behaviour) and optical properties of EVA-rich and ethylene-alpha-olefin copolymer-rich blends were studied and the results are discussed in terms of processibility in film applications. 24 refs. 

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