Introduction to EVA
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Alternative name: Ethylene-vinyl acetate copolymer. English name: ethylene-vinyl acetate copolymer; EVA. Physical and chemical properties: EVA copolymer is a high-molecular-weight thermoplastic polymer and is a typical random copolymer. By introducing short side chains composed of polar acetate groups into the ethylene backbone, EVA disrupts its original crystalline structure, causing it to exhibit a \"plasticization effect\" that reduces the crystallinity of the ethylene in these side chains, while also increasing the distance between the polymer chains. This makes EVA more flexible and elastic than PE. The steric hindrance caused by the CH3COO groups in EVA copolymers is a crucial factor that results in significant differences between its crystallinity and glass transition temperature and those of high-pressure polyethylene; it also affects its thermal stability, aging properties, and other physical and mechanical properties. As the VA content in EVA increases, its crystallinity decreases linearly. At the same time, the density of the EVA copolymer and its permeability to water vapor increase, while its stiffness and Vicat softening point decrease; moreover, its resistance to environmental stress cracking improves. EVA has better low-temperature resistance than polyethylene. The melt index (MI) of EVA is related to the polymerization conditions as well as the VA content; under the same polymerization conditions, the higher the VA content, the higher the MI. The dielectric constant and dielectric loss tangent of EVA have a linear relationship with the content of VA in the copolymer; in other words, the higher the content of VA, the greater the dielectric constant of EVA. The thermal decomposition temperature of EVA is 229–230°C; however, some studies indicate it to be above 250°C as well. Therefore, this property should be taken into account when processing EVA. During processing, it can be judged by observing whether there is an acetic acid odor and the degree of change in the product’s color. The optical properties of EVA films are generally superior to those of polyethylene. EVA films are flexible, and their impact strength is higher than that of low-density polyethylene. EVA has a higher permeability to gases and moisture than LDPE, so it is not used as a highly impermeable material. EVA has slightly poorer oil and chemical resistance compared to PE and PVC, and this tendency becomes more pronounced as the VA content increases. Uses: It can be used as shrink film for packaging, repackaging bags, and sheaths for flexible wires and cables. It is also commonly employed in injection and blow-molded products, hot melt adhesives, coatings for various sheets and papers, and foam products. EVA can also be used as a modifier for other resins, and its copolymers are used as petroleum antifreeze agents.
I saw EVA yesterday and wanted to learn more about it; thanks to the original poster
Ethylene-vinyl acetate copolymer (also known as ethylene-vinyl acetate polymer) is produced by the copolymerization of ethylene (E) and vinyl acetate (VA); its English name is Ethylene Vinyl Acetate, abbreviated as EVA, or E/VAC. The polymerization methods include high-pressure bulk polymerization (for plastics), solution polymerization (for PVC processing aids), emulsion polymerization (for adhesives), and suspension polymerization. Emulsion polymerization is used when the vinyl acetate (VA) content is above 30%, while high-pressure bulk polymerization is employed when the vinyl acetate content is low. Properties and Applications of Ethylene-Vinyl Acetate Copolymers I. Properties EVA resin is characterized by its good flexibility and rubber-like elasticity; it retains good ductility even at -50°C. It also has good transparency and surface gloss, excellent chemical stability, strong resistance to aging and ozone, and is non-toxic. It has good mixing properties with fillers, as well as good coloring and molding properties. It is highly related to the vinyl acetate content, molecular weight, and melt index. When the melt index (MI) remains constant, an increase in the vinyl acetate (VAC) content leads to improvements in elasticity, softness, compatibility, and transparency as well. As the VAC content decreases, the properties approach those of polyethylene; rigidity increases, while wear resistance and electrical insulation improve. When the VAC content remains constant, an increase in the melt index leads to a decrease in the softening point; processing properties and surface gloss improve, but strength decreases. Otherwise, as the MI decreases, the molecular weight increases, resulting in improved impact resistance and resistance to environmental stress cracking. The polarity of acetate groups increases elasticity and viscosity, reduces crystallinity and electrical properties, and it is soluble in hydrocarbon solvents and oils. II. Applications EVA resin has a wide range of applications. Generally, for EVA with a vinyl acetate content of 5% or less, its main products include films, wires and cables, LDPE modifiers, adhesives, etc ； EVA products with a vinyl acetate content of 5% to 10% are used for elastic films and similar applications ； EVA with a vinyl acetate content of 20–28% is primarily used in hot-melt adhesives and coated products ； The vinyl acetate content ranges from 5% to 45%. The main products include films (including agricultural films) and sheets, injection-molded and molded products, foam products, hot-melt adhesives, etc. For example: (1) Films, sheets, and laminated products: They possess properties such as sealing ability, adhesiveness, flexibility, toughness, and compressibility. They are suitable for use in elastic packaging films, heat-shrinkable films, agricultural films, food packaging films, and laminated films; they can also be used as intermediate layers in polyolefin laminated films. (2) General-purpose items: They possess advantages such as flexibility, resistance to environmental stress cracking, and good weather resistance. Materials suitable for industrial use include insulation covers for electrical wires, components for household appliances, and window sealing materials. (3) The category of daily necessities includes sports equipment, toys, seat cushions, straps, sealed container lids, EVA rubber soccer balls, etc. (4) Auto parts include shock absorbers, fenders, and interior and exterior decorative accessories. (5) Foamed products: Pressure-foamed products include foam plastic slippers, sandals, building materials, etc. Injection molding foaming is used for various industrial components, women’s shoe soles, hot-melt adhesives, and more. Molding of ethylene-vinyl acetate copolymers: EVA can be molded by injection molding, extrusion, blow molding, calendering, rotational molding, vacuum thermoforming, foaming, coating, heat sealing, welding, and other methods.
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