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EVOH Resins

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  • Ethylene Vinyl Alcohol, commonly abbreviated EVOH, is a formal copolymer of ethylene and vinyl alcohol. Because the latter monomermainly exists as its tautomer acetaldehyde, the copolymer is prepared by polymerization of ethylene and vinyl acetate to give the ethylene vinyl acetate (EVA) copolymer followed by hydrolysis.

  • The vinyl alcohol base has exceptionally high gas barrier properties, but it is water soluble and dif?cult to process.

  • EVOH copolymers are highly crystalline, and their properties are highly dependent on the relative concentration of the comonomers. Generally speaking, as the ethylene content increases, the gas barrier properties decreases, the moisture barrier properties improve, and the resins are processed more easily.

  • One of the major applications for EVOH is in auto-motive fuel systems to control emissions of hydro-carbons from fuel lines and tanks.

  • The first and foremost producer of EVOH (ethylene vinyl-alcohol copolymer resins) under the name EVAL™ and the manufacturer of KURARISTER™ film, today the Kuraray Group consists of about 70 companies, employing around 7,000 people worldwide.

  • Ethylene vinyl alcohol copolymer (EVOH) is a barrier resin often used in multilayer food packages and blow-molded rigid containers. The production of EVOH is a two-step process of polymerization and saponification. First, ethylene and vinyl acetate are polymerized using an initiator/activator complex. Second, the ethylene-vinyl acetate copolymer (EVAc) is saponified to ethylene vinyl alcohol copolymer.

  • As of 2003, the production of EVOH is done primarily by two Japanese companies. Kuraray and Nippon Synthetic have manufacturing facilities in Japan, the United States and Europe. EVAL Company of America (EVALCA) is a subsidiary of Kuraray. EVALCA opened a plant in Pasadena, Texas in 1986.

  • Kuraray uses a proprietary system for copolymerization using solution polymerization with a heat exchanger. Their method entails simultaneously passing the solvent solution of vinyl acetate and discharged ethylene through a heat exchanger provided with a cooling means, thus, causing the solution of vinyl acetate to absorb and solubilize ethylene before the solution returns to the polymerization vessel. In the vessel, the vinyl acetate with solubilized ethylene is mixed with the polymerization solution. Saponification is done with a two-stage process patented by Kuraray to achieve a high degree of saponification (99.5%) with less alkali catalyst by using different conditions corresponding to the differences in reaction mechanism between initial and final stages of EVAc saponification. The process uses methanol as a solvent and a sodium hydroxide catalyst. The EVOH product is extruded into polymer pellets and stored for shipping.

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