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مادة الـ E.v.a

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    lion1550
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    تاريخ التسجيل: Feb 2006
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    مادة الـ E.v.a

    بدأت العمل في معمل لصناعة الأحذية وأريد معلومات عن مادة الإيفا E.v.a ( ايتيلين فينيل اسيتات )
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  2. [2]
    chopin
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    تاريخ التسجيل: Jan 2003
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    Ethylene-vinyl acetate
    Ethylene-vinyl acetate (also known as EVA or sometimes simply as "acetate") is the copolymer of ethylene and vinyl acetate. It is a polymer that approaches elastomeric materials in softness and flexibility, yet can be processed like other thermoplastics. The material has good clarity and gloss, barrier properties, low-temperature toughness, stress-crack resistance, hot-melt adhesive and heat sealing properties and resistance to UV radiation. EVA has little or no odor and is competitive with rubber and vinyl products in many electrical applications.

    EVA foam is used as padding in equipment for various sports such as hockey, boxing, and mixed martial arts.

    EVA is also used in Biomedical Engineering applications as a drug delivery device. The polymer is dissolved in an organic solvent (e.g., methylene chloride). Powdered drug and filler (typically an inert sugar) are added to the liquid solution and rapidly vortexed to obtain a homogeneous mixture. The drug-filler-polymer mixture is then cast into a mold at -80 degrees and freeze dried until solid. These devices are used in drug delivery research to slowly release a compound over time. While the polymer is not biodegradable within the body, it is quite inert and causes little or no reaction following implantation.

    EVA is also the same material found at the bottom of many tennis shoes.



    based on copolymerisation products of ethylene with vinyl acetate and are normally produced either from bulk continuous polymerisation or solution polymerisation. The former produces low molecular weight copolymers useful for coatings, hot melt adhesives, etc., whilst the latter yields high molecular weight products for tougher applications.

    As the level of vinyl acetate in the copolymer increases so the level of crystallinity found in polythene alone reduces from about 60% to 10%. This yields products ranging from materials similar to low density polythene to flexible rubbers. Common grades can contain from 2% to 50% vinyl acetate. Clarity, flexibility, toughness and solvent solubility increase with increasing vinyl acetate *******. Of particular note is the retention of flexibility of EVA rubber grades down to (-70C) and because they are copolymers, problems due to plasticiser migration are not experienced.

    Good resistance to water, salt and other environments can be obtained but solvent resistance decreases with increasing vinyl acetate *******. The copolymers can accept high filler and pigment loadings. Being thermoplastic EVA can be moulded by extrusion, injection, blow moulding, calendaring and rotational moulding. Crosslinking with peroxides can produce thermoset products.

    Applications are diverse, such as flexible shrink wrap, footware soles, hot melt and heat seal adhesives, flexible toys, tubing, wire coatings, medical gloves, masks, babies’ dummies and bottle teats. Crosslinked foamed tyres have been used for tough service. Many grades and modifications now exist to meet modern demands from these versatile EVA copolymer types.

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  3. [3]
    Eng.Foam
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    تاريخ التسجيل: Oct 2006
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  4. [4]
    lion1550
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