The common ethylene-vinyl acetate copolymer is thermoplastic, with a VA content of 5-45%. With the increase of VA content, the density, crystallinity, melting point, transparency, flexibility, low temperature performance, stress cracking resistance and polarity of EVA are all improved. When the content of VA is less than 25%, EVA is a special plastic. When the content of VA is more than 25%, it is an elastomer with excellent flexibility and resilience. Because the content of VA also affects the polarity of molecules, when the content of VA is greater than 18%, EVA can be dissolved in common solvents, and its solubility increases with the increase of VA, and EVA with high VA content is easily corroded by oil. Typical properties of EVA with different VA contents are shown in the following table.
Most ethylene-vinyl acetate copolymers have a melt index between 2 and 500. EVA can be processed on standard plastic molding equipment, and its processing performance is similar to LDPE. When the temperature exceeds 230℃, the ester bond of vinyl acetate will be broken and acetic acid will be released. Therefore, the processing temperature of EVA should be lower than 230℃. Even at normal processing temperature, a small amount of acetic acid will be released, so ethylene-vinyl acetate copolymer and its products can smell slightly sour. In order to avoid corrosion of processing equipment, LDPE puncher should be used after processing EVA to ensure that there is no EVA residue in the equipment when it is stopped. ?
EVA is mainly used in packaging, greenhouse film, wires and cables, adhesives, coatings and composite materials. In the field of packaging film, EVA is mainly used for antifreeze packaging film, heat sealing film and stretching film. These are all based on its low temperature resistance, low melting point and high elasticity. EVA is often added to the greenhouse film to improve the thermal insulation performance of the greenhouse. Using the polarity of VA, EVA with high VA content and high melt index is often used in the production of hot melt adhesives. It is also used to coat BOPET or BOPP to produce card protective film or hot film. In addition, EVA is also used as the carrier resin of color masterbatch or filler masterbatch and the insulating material of wire and cable by its compatibility with different materials and good dispersibility with inorganic fillers.