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Ethylene vinyl acetate (EVA)
0.75-4 usd/kg
Polymerising polyethylene with vinyl acetate (EVA) produces a very tough, rubber-like, semi-opaque thermoplastic with a relatively low upper working temperature. The vinyl acetate content is adjusted, according to the application, and as a result a range of properties can be achieved. EVA is utilised in moulding, extrusion, films, coatings, adhesives and foams.
Its inherent flexibility and toughness, combined with plasticiser-free chemistry, means it presents an attractive alternative to polyvinyl chloride (PVC) and polyurethane resin (PUR), in some cases.
As a thermoplastic, it is relatively easy to recycle with melt-processing techniques, such as compounding and extrusion. The difficulty with EVA is that it is often combined with other materials, and used as an adhesive interlayer, which makes it challenging, if not impossible, to recycle.
Sustainability concerns
Non-renewable ingredients
Raw material generates polluting by-products
Microplastics
Ethylene vinyl acetate (EVA) foam is used for its softness, colour, durability, especially at low temperatures, and resistance to weathering and water. As it does not contain plasticiser, it is suitable for use in toys, sports equipment (yoga blocks, rollers, martial arts padding, helmet inserts, for example), floatation (swimming pool toys and aids), packaging and food contact applications, for example. It is also used in gaskets and industrial applications.
EVA foam us applied as cushioning in footwear, such as to provide comfort as a midsole or outsole. Indeed, entire shoes are produced from injection moulded EVA foam, such as Crocs. It takes colour well, and available in bright, saturated hues. EVA is resilient, but not as long lasting as natural rubber, or leather. And it will be more slippery than rubber.
It is possible to cross-link EVA foam, during injection moulding or slab extrusion, to produce a material with higher resilience, shock absorption and chemical resistivity. Cross-linking, which is also commonly applied to polyethylene (PE) foam, forms chemical connections between neighbouring polymer chains. This helps to stabilise bubbles during foam expansion, and so enhances the resistance of the foam to thermal collapse. There are several methods used including irradiation and chemical cross-linking.
