WHAT IS EVA
Ethylene-Vinyl Acetate (EVA), also known as poly (ethylene-vinyl acetate) (PEVA), is the copolymer of ethylene and vinyl acetate. The weight percent vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene.
Broadly speaking, there are three different types of EVA copolymer, which differ in the vinyl acetate (VA) content and the way the materials are used.
The EVA copolymer which is based on a low proportion of VA (approximately up to 4%) may be referred to as vinyl acetate modified polyethylene. It is a copolymer and is processed as a thermoplastics material – just like low density polyethylene. It has some of the properties of a low density polyethylene but increased gloss (useful for film), softness and flexibility. The material is generally considered as non-toxic.
The EVA copolymer which is based on a medium proportion of VA (approximately 4 to 30%) is referred to as thermoplastic ethylene-vinyl acetate copolymer and is a thermoplastic elastomer material. It is not vulcanized but has some of the properties of a rubber or of plasticized polyvinyl chloride particularly at the higher end of the range. Both filled and unfilled EVA materials have good low temperature properties and are tough. The materials with approximately 11% VA are used as hot melt adhesives.
The EVA copolymer which is based on a high proportion of VA (greater than 60%) is referred to as ethylene-vinyl acetate rubber.
EVA is an elastomeric polymer that produces materials which are “rubber-like” in softness and flexibility. The material has good clarity and gloss, low-temperature toughness, stress-crack resistance, hot-melt adhesive waterproof properties, and resistance to UV radiation. EVA has a distinctive vinegar-like odor and is competitive with rubber and vinyl polymer products in many electrical applications.
WHAT IS THE APPLICATION OF EVA
Hot melt adhesives (such as hot glue sticks) and top-of-the line soccer cleats are usually made from EVA, generally with additives like wax and resin. EVA is also used as a clinginess-enhancing additive in plastic wraps. Craft-foam sheets are made of EVA and are popularly used for children’s foam stickers.
EVA is also used in biomedical engineering applications as a drug-delivery device. The polymer is dissolved in an organic solvent (such as dichloromethane). Powdered drug and filler (typically an inert sugar) are added to the liquid solution and rapidly mixed to obtain a homogeneous mixture. The drug-filler-polymer mixture is then cast into a mold at −80 °C and freeze-dried until solid. These devices are used in drug delivery research to slowly release a compound. The polymer does not biodegrade within the body, but is quite inert and causes little or no reaction following implantation.
EVA is one of the materials popularly known as expanded rubber or foam rubber. EVA foam is used as padding in equipment for various sports such as ski boots, bicycle saddles, hockey pads, boxing and mixed-martial-arts gloves and helmets, wakeboard boots, waterski boots, fishing rods and fishing-reel handles. It is typically used as a shock absorber in sports shoes, for example. (Some manufacturers of running shoes, such as Nike, market EVA-based compression-moulded foam used in the manufacture of running shoes as “Phylon”.) It is used for the manufacture of floats for commercial fishing gear such as purse seine (seine fishing) and gillnets. In addition, because of its buoyancy, EVA has made its way into non-traditional products such as floating eyewear. It is also used in the photovoltaics industry as an encapsulation material for crystalline silicon solar cells in the manufacture of photovoltaic modules. EVA slippers and sandals are popular, being lightweight, easy to form, odorless, glossy, and cheaper compared to natural rubber. In fishing rods, EVA is used to construct handles on the rod-butt end. EVA can be used as a substitute for cork in many applications.
PVAc copolymers are adhesives used in packaging, textile, bookbinding for bonding plastic films, metal surfaces, coated paper and as redispersible powders in plasters and cement renders.
Flower-making foam is a thin sheet made of EVA, which is flexible, and is used to make artificial flowers. These foams are presented as raw sheets and they can be cut into the desired petal shape and then can be formed by ironing to assemble artificial flowers by putting these petals together.
EVA is also used in coatings formulation of good-quality interior water-borne paints at 53% primary dispersant.
Hydrolysis of EVA gives ethylene vinyl alcohol (EVOH) copolymer.
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