EVA copolymer

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. 

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. 

Fig. 3. Melting point and crystallinity vs. weight percent VA in EVA copolymers. (Courtesy of Exxon Chemical Company.)...

Specialty waxes include polar waxes for more polar adhesive systems. Examples would be castor wax (triglyceride of 12-hydroxy stearic acid) or Paracin wax N- 2 hydroxy ethyl)-12-hydroxy stearamide) which are used in polyester, polyamide, or with high VA EVA copolymer-based systems. Other common polar waxes are maleated polyethylenes, which are used to improve the specific adhesion of polyethylene-based adhesives, and low molecular weight ethylene copolymers with vinyl acetate or acrylic acid, which are used to improve low temperature adhesion. High melting point isotactic polypropylene wax (7 155°C) and highly refined paraffin wax (7,n 83°C) are used where maximum heat resistance is critical. Needless to say, these specialty waxes also command a premium price, ranging from 2 to 5 times that of conventional paraffin wax. 

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. 

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]. 

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... 

TGA, iodometric, mid-IR, luminescence (fluorescence and phosphorescence) and colour formation (yellowness index according to standard method ASTM 1925) were all employed in a study of aspects of the thermal degradation of EVA copolymers [67], Figure 23 compares a set of spectra from the luminescence analysis reported in this work. In the initial spectra (Figure 23(a)) of the EVA copolymer, two excitation maxima at 237 and 283 nm are observed, which both give rise to one emission spectrum with a maximum at 366 nm weak shoulders... 

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). 

Figure 69 shows the ATR-FTIR spectra of the inside heat seal layer of the white film from both the "good" and "bad" packages. A library spectrum of an EVA copolymer is also shown for comparison. The heat seal layer is identified as EVA, based on the position of peaks in the sample spectra compared to the library EVA spectrum. The heat seal layer appears to have a lower vinyl acetate content compared to the library spectrum, which was acquired from a 14% vinyl acetate copolymer. There were no significant spectral differences between the spectra of the "good" and "bad" samples. 

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... 

EVA copolymers are made with a range of VA content, usually between 15 and 22%, which means that the overall crystallinity is about 20%, lower than the 40 to 50% for LDPE. The crystalline regions in EVA have a melting temperature of about 70 °C, compared with about 110 °C in metallocene LDPE. 

Eaves (92) distinguished between polyolefin plastomers (POP) with density >910 kg m and polyolefin (POE) elastomers with densities <910 kg m-3. The density of a polyethylene at 20 °C is a linear function of the crystallinity, with limiting values of 854 kg m 2 for zero crystallinity and 1000 kg m for 100% crystallinity. The polyolefin elastomer foams compete with EVA copolymer foams. Metallocene chemistry also allows the production of copolymers with a larger comonomer content in the high molecular weight part than in the low molecular weight part this... 

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. 

BXL Plastics ERP division is introducing two new grades of antistatic and conductive foams at this years Intemepcon exhibition at the Birmingham NEC in the UK in March 1988. Brief details are given on conductive closed-cell crosslinked EVA copolymer foam, Evazote C, and antistatic PE foam Plastazote AS, both used for electronics packaging. 

Henderson AM (1993) Ethylene-vinyl acetate (EVA) copolymers a general review. Electrical Insulation Magazine 9 30-38... 

The most common type of wax crystal modifier used to reduce the pour point and filtration temperature of distillate fuel is based on ethylene vinylacetate (EVA) copolymer chemistry. These compounds are quite common throughout the fuel additive industry. The differences, however, are found in the variation in the molecular weight and the acetate ratio of the copolymer. 

On occasion, the performance of an EVA copolymer can be enhanced by blending with a wax crystal modifier of a different chemical type. Wax crystal modifiers used to modify the crystal structure of lubricant, residual fuel, and crude oil waxes can be blended at low concentrations with EVA copolymers to improve their performance. However, the performance enhancement is usually fuel specific and not broad ranged. Also, the low-temperature handling properties of the EVA may be impaired when blended with other wax crystal modifiers. 

Materials. Polyethylene (PE) Low density polyethylene (PE) and ethylene-vinyl acetate (EVA) copolymers with vinyl acetate (VA) contents of 9, 18, 25, 28, 33, and 40% were obtained from Scientific Polymer Products, Inc. 

Chauve et al. [253] utilized the same technique to examine the reinforcing effects of cellulose whiskers in EVA copolymer nanocomposites. It was shown that larger energy is needed to separate polar EVA copolymers from cellulose than for the nonpolar ethylene homopolymer. The elastomeric properties in the presence of spherical nanoparticles were studied by Sen et al. [254] utilizing Monte Carlo simulations on polypropylene matrix. They found that the presence of the nanofillers, due to their effect on chain conformation, significantly affected the elastomeric properties of nanocomposites. 

The reaction vessel is purged with nitrogen gas and heated up to 60°C at an ethene pressure of 4.6 MPa. Then, an aqueous solution of hydrogen peroxide and an aqueous solution of sodium erysorbate aqueous solution are added. The catalyst dosage is repeated at the end of the polymerization (9). Vinyl EVA copolymer emulsions can be directly produced with a content of solids of 65-75% (10). 

Various methods have been employed to incorporate very large amounts of functionalized monomers into EVA copolymers. Physical blends of EVA copolymers and polymers of acrylic acid have been described (12). 

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. 

In the saponification of an EVA copolymer, usually an alkali catalyst is used. The alkali catalyst acts as a catalyst for the transesterification between EVA and an alcohol. It is known that in a process where saponification proceeds mainly with this transesterification, when water is present in the reaction system, the alkali catalyst is consumed, and the reaction rate of the saponification decreases. 

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