EVA polymers

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. 

EVA polymers have been important for film manufacture. They are not competitive with normal film because of the high surface tack and friction which make them difficult to handle on conventional processing machinery. However, because of their somewhat rubbery nature, gloss, permeability, and good impact... 

It is interesting to note that these crystalline materials do not dissolve in tetrahydrofuran or cyclohexanone at room temperature, indicating that PVC is too weak a proton donor to overcome extensive crystallisation. Crystalline PVC has a greater tensile strength and creep resistance than conventional polymer. It is, however, brittle, and whilst most conventional impact modifiers appear ineffective, EVA polymers are said to be quite useful. Plasticised compounds may also be prepared although mixing temperatures of up to 190°C are necessary. 

Aqueous-based EVA polymer emulsions suited for the use in heat seal applications are produced at a comparatively low pressures process, less than 14 M Pa (2). 

The EVA polymer emulsions contain crystalline segments resulting from ethylene linkages. In addition to ethylene and vinyl acetate, a carboxylic comonomer is used, such as acrylamide or versa tic acid vinyl ester. The polymers have crystalline melting point of 50-90°C. 

A preferred way to enhance the crystalline domain formation of ethylene in the EVA polymer is to delay the addition of vinyl acetate during the polymerization process such that the unreacted vinyl acetate level present in the reactor is minimal at different stages during the process. Thus, the copolymerization can take place in the initial stage, where most of the ethylene will reside in amorphous regions, and the formation of the majority of crystalline ethylene domains can occur in the later stage of the polymerization process. 

Blends of aliphatic-aromatic copoly(ester)s with EVA polymers have a higher melt strength than the aliphatic-aromatic copoly(ester)... 

It has been found that in the development of EVA polymers for heat seal applications by emulsion polymerization that the concentration of vinyl acetate and ethylene in the polymer is not solely responsible for its use as a heat seal adhesive (2). 

Adjacent ethylene segments lead to ethylene crystallinity in the polymer. An improper amount can result in EVA polymers, which have little adhesion in terms of hot green strength and room temperature adhesive strength, but pass the non-blocking test or they may have desired adhesion but are do not meet the non-blocking test at desired temperature and pressure. 

In EVA polymers the glass transition temperature of the polymer can be controlled by adjusting the ethylene content. As more ethylene is present in the polymer as lower is the glass transition temperature. However, under certain conditions of polymerization the formation of crystalline poly(ethylene) domains are favored. 

Examples for commercially available EVA polymers and suppliers as well are shown in Table 7.4. Tradenames appearing in the references are shown in Table 7.3. 

Considering heterogeneous models for the film structure, we realize that if PVC with its low permeability were the continuous phase, there should only be small increases in permeability with the addition of EVA polymer. Such effects have been observed for a system of butadiene-based polymer modifier added to PVC to increase the impact strength (1). Addition of 15% modifier increased the permeability less than 10%. Electron micrographs of this film showed that the butadiene-based modifier was dispersed in the PVC phase. 

The UL 1685 tray cable burn test was conducted on a cable construction with three different jacketing materials consisting of EVA polymer with 60 wt % Mg(OH)2 (EVA-MH), EVA polymer with 58 wt % Mg(OH)2 and 2wt % nanoclay (EVA-MH-NanoM), and 1 1 EVA PE with 58 wt %... 

Figure 1. Grafting of a small amount of monomer onto an EVA polymer...

Figure 3.9 TG analyses of EVA polymer degradation by both thermal treatment and catalytic cracking over a MCM-41 material [45]. (Reproduced with permission from Elsevier)...

Ethylene-vinyl acetate (EVA) polymers (containing 65%-70% by weight of vinyl acetate) are of industrial interest as high-molecular weight plasticizers for PVC, mainly because of their low cost. A polymeric plasticizer PB-3041 available from Du Pont allows the preparation of a highly permanent plasticized PVC formulation. It is believed to be a terpolymer of ethylene, vinyl, acetate, and carbon monoxide. Also, butylene terephthalate-tetrahydrofuran block copolymers, with the trade name of Hytrel (Du Pont), are used as excellent permanent plasticizers of PVC. 

PVC formulations are generally ethylene vinyl acetate (EVA) polymer-based, chlorinated polyethylene (CPE)-based, or acrylic-based. The majority of new grades are acrylic-based and are claimed to exhibit greater impact strength than the other two types. 

Plastics find extensive use in several areas of fiber optic cables. Buffer tubes, usually extruded from high-performance plastics such as fluoropolymers, nylon, acetal resins, or polybutylene terephthalate (PBT) are used for sheathing optical fibers. A blend o PVC and ethylene vinyl acetate (EVA) polymer, such as Pantalast 1162 of Pantasote Incorporated, does not require a plasticizer, which helps the material maintain stability when in contact with water-proofing materials. PVC and elastomer blends, Carloy 6190 and 6178, of Cary Chemicals are also used for fiber optic applications (Stiffening rods for fiber optics are either pultruded epoxy and glass or steel. Around these is the outer jacketing, which is similar to conventional cable.)... 

Figure 3 shows the performance during static oven aging at 170°C (338°F) of a stabilized EVA polymer. The base stabilization of the EVA polymer by the producer using AO-1 provided an unsatisfactory level of stability. The presence of skinning and a more pronounced level of discoloration in the base AO-1 stabilized EVA requires additional antioxidant to meet the performance needs of a HMA. Upon the addition of AO-2 to the base polymer, it is clear that the stability of the EVA is improved significantly, skin formation is not observed, and color development is reduced substantially. The formation of insoluble gel as a result of cross-linking is also reduced dramatically with the addition of AO-2, as shown in Fig. 4. 

Figure 3 Discoloration of EVA polymer Gardner color, days at 170°C (338°F).

PVC resin BaZn stabihzer Calcium carbonate EVA polymer DOP plasticizer Stearic acid lubricant Titanium dioxide Pigment... 

Zanetti, M. and Costa, L. 2004. Preparation and combustion behaviour of polymer/layered silicate nanocomposites based upon PE and EVA. Polymer 45 4367-4373. 

Ethylene-vinyl acetate copolymers, usually known as EVA, are used in many applications, but especially for low voltage cables. These polymers are easily flammable and flame retardants are added to reduce their flammability. The classic solution is to incorporate aluminium hydroxide or magnesium hydroxide that develop endothermic reactions when heated. Nevertheless, large amounts have to be incorporated, often around 60% and this can lead to a loss of mechanical properties in the compound. Intumescent technology that works well with polypropylene has also been tried for EVA polymer systems. 

Ethylene is copolymerized with many nonolefinic monomers, particularly acrylic acid variants and vinyl acetate, with EVA polymers being the most commercially significant. All of the copolymers discussed in this section necessarily involve disruption of the regular, crystallizable PE homopolymer and as such feature reduced yield stresses and moduli, with improved low-temperature flexibihty. 

Accelerated tests have shown that EVA copolymers resist degradation by weathering better than conventional polyethylene. However, chemical resistance and barrier properties of EVA copolymers are inferior. EVA polymers accept high degrees of filler loading without serious degradation of their physical properties. 

PCU/EVA polymer blend consisting of poly(carbonate urethane) and... 

---