Ethylene-vinyl acetate copolymer characteristics

Implants in the rabbit corneas exhibited no observable inflammatory characteristics over a period of 6 weeks. Compared to other previously tested polymers, the inertness of these polyanhydrides rivals that of the biocompatible poly(hydroxyethyl methacrylate) and ethylene-vinyl acetate copolymer. Histological examination of the removed corneas also revealed the absence of inflammatory cells (21)... 

The most widely used thermoplastic polymer is the ethylene—vinyl acetate copolymer, which is obtainable in a wide range of molecular weights as well as in a variety of compositions. Often flexibilizers or plasticizers are added in order to improve both the mechanical shock resistance and the thermal properties of the adhesive. Polybutenes, phthalates, and tricresyl phosphate have been used as plasticizers. Tackifying agents can also be added. Because hot-melt adhesives are frequendy ethylene-based, they are subject to oxidation if, as in a typical situation, the adhesive sits in an applicator for long periods before use. Thus, antioxidants such as hindered phenols are often used, as are fillers. Fillers are added to opacify or to modify the adhesive s flow characteristics, as well as to reduce cost. Wax is also a very important component. Wax alters surface characteristics by decreasing both the liquid adhesive s surface tension and its viscosity in the melt. Upon solidification, however, the wax acts to increase the strength of the adhesive. Both paraffin and microcrystalline wax are used (see Waxes). 

Acrylonitrile-butadiene rubber, NBR, styrene-aciylonitrile rubber, SAN, ethylene-vinyl acetate copolymer, EVA, and acrylic copolymers are helpful modifications of polyvinylchloride that change its processing characteristics and elastomeric properties. Blending with these copolymers helps to reduce the requirement for low molecular weight plasticizers. Ethylene-vinyl acetate copolymer plays a role of high molecular weight plasticizer in production of vinyl hose. This reduces the amount of DOP used in flexible hose applications. Ethylene copolymer is used plasticize PVC that reduces gel. "" Phthalate plasticizers can be eliminated from water based adhesives because of utilization of vinyl acetate ethylene copolymer as a high molecular plasticizer/modifier. " ... 

Ethylene-vinyl acetate copolymers can be thought of as modified high pressure polyethylenes. Because of the free-radical polymerization process they have structural characteristics such as short-chain and long-chain branching in addition to the effects due to the incorporation of the vinyl acetate comonomer. Ethylene and vinyl acetate have a reactivity ratio which is close to 1 and as a result EVA copolymers contain vinyl acetate which is homogeneously distributed among the polymer chains. The major effect of the VA on polymer properties is to reduce... 

Characteristics of Gels Formed from Ethylene Vinyl Acetate Copolymers in Xylene at 24 C... 

P. Cusack, M. Cross, and P. Hornsby, Effects of tin additives on the flammability and smoke emission characteristics of halogen-free ethylene-vinyl acetate copolymer. Polymer Degradation and Stability, 79 (2003), 309-18. 

C. M. Jiao, Z. Z. Wang, X. L. Chen, and Y. Hu, Synthesis of a magnesium/ aluminum/iron layered double hydroxide and its flammability characteristics in halogen-free, flame-retardant ethylene/vinyl acetate copolymer composites. Journal of Applied Polymer Science, 107 (2007), 2626-31. 

Feller, R. L., Curran, M. (1970). Solubility and crosslinking characteristics of ethylene/vinyl acetate copolymers. Bulletin of the American Group of the International Institute for Conservation, 77(1), 42-45. 

Ethylene vinyl acetate copolymers (EVA) polyolefin plastics whose properties resemble polyethylene but are more easily processed. EVA films are used for food packaging, and as outer layers for greenhouses. Tubing is used for medical and beverage dispensing. Properties include outstanding flexibility, clarity, resilience and low temperature characteristics. 

The most common copolymer of this type is ethylene-vinyl acetate, which we normally refer to as EVA. This variety of polyethylene is illustrated in Fig. 18.2 e), in which the ester branches are indicated by the symbol VA This family of copolymers is commercially available containing vinyl acetate concentrations of up to approximately 25 mole %. In addition to the randomly distributed ester branches, these resins also contain the short and long chain branches that are characteristic of low density polyethylene. 

Instead, the distribution of vinyl acetate and ethylene in the copolymer is a major factor. A sufficient level of amorphous ethylene vinyl acetate polymer segments is needed in order to provide adhesion to a substrate. Further, a sufficient level of crystalline ethylene polymer segments is needed to provide the proper balance of heat seal characteristics and non-blocking. 

Figure 3 shows the solubility characteristics of the vinyl acetate copolymers in MEK note the improved solubility over the homopolymers of vinyl chloride. Because these copolymers are still significantly less soluble than the metal adhesion terpolymers, one manufacturer has produced a copolymer not based on vinyl acetate (see Figure 3, high solubility copolymers). This copolymer is described in more detail in Figure 13. Copolymers are also available based on vinyl chloride-trifluorochloro-ethylene and vinyl chloride-vinylidene chloride.

Several types of insulator materials— Teflon, polyethylene, polystyrene, silicon, dacron, ioplexes, ethylene-vinyl acetate and ethylene acrylic acid copolymers, glass, etc.—have been examined for their electrokinetic characteristics. In some of these cases, the surface charge characteristics have been modified by prior electrical or chemical treatment. The correlations which have been drawn between the electrokinetic and anti- or prothrombogenic characteristics of these materials are presented in the next section. 

In 2003 Dow introduced three classes of compatibiliser, i.e., maleated polyolefins, ethylene-vinyl acetate and ethylene-ethyl acrylate copolymers, all imder the Amplify name. They were intended to improve the impact and viscosity characteristics of engineering thermoplastics and polyolefins for use in domestic appliance and automotive components, as well as for coatings and adhesives. 

Ethylene can also be copolymerized with polar monomers in order to widely modify the characteristics of the corresponding materials. The comonomers are most often (meth)acrylic monomers or vinyl acetate, with the latter being the most used for the production of EVA copolymers (ethylene/vinyl acetate). EVAs generally contain about 20% mass of comonomer and are very interesting due to their adhesive properties. 

Copolymers of ethylene vinyl acetate (EVA) grades Evatane 2020 and Evatane 2805 (Arkema) and Sevilen 11306-075 brand of JSC Sevilen (TU 6-05-1636-97) copolymer of ethylene vinyl acetate and maleic anhydride (EVAMA) grades Orevac 9305 and Orevac 9707 (Aikema) were used as the objects of the study. The main characteristics of the polymers are listed in the Table 1. 

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