• EVA is a random copolymer of ethylene and vinyl acetate. Due to the introduction of a polar acetic acid group in the ethylene chain formed by the short branch, the original crystalline state is changed, making EVA more flexible and elastic than polyethylene.
• The performance of EVA resin has a great relationship with the content of vinyl acetate and the melt flow rate. When the MFR is constant, with the increase of vinyl acetate content, its elasticity, flexibility, compatibility and transparency are improved, and the crystallinity is decreased; with the decrease of vinyl acetate content, the performance is close to polyethylene, the rigidity increases, the wear resistance and the electrical insulation performance are improved. If the vinyl acetate content is certain, when the MFR increases, the softening point decreases, the processability and surface gloss are improved, but the mechanical strength decreases; on the contrary, with the decrease of MFR, the molecular weight increases, the impact resistance and stress cracking resistance are improved.
• EVA is often blended with other polymers as a modifier because of its good flexibility, toughness, stress crack resistance and adhesive properties. Blends of polyethylene and ethylene vinyl acetate copolymer (EVA) are widely used because of their excellent flexibility, processability, good air permeability and printability.
• Polyethylene and EVA blends with EVA blending amount, EVA VAc content, EVA molecular weight, blend system and processing conditions and many other factors change and show different properties.
• The effect of VAc content in EVA is very significant. When the content of VAc in EVA is low (6.6%), the amount of EVA incorporation has no effect on the crystallinity. The effect of EVA incorporation on density is obvious, that is, the density of the blend increases with the increase of EVA incorporation, especially after the EVA content reaches 25%, the increase is faster. EVA with a large amount of VAc has a great effect on PE modification, whether it is crystallinity or density, there is a sharp change, and increasing the VAc content in EVA also leads to a rapid increase in the elongation of PE/EVA blends. The modification effect produced by increasing the proportion of EVA in PE/EVA is generally similar to the effect of increasing the VAc content in EVA.
• EVA can modify the impact properties and environmental stress cracking resistance of HDPE. This is because the longer branches of the EVA molecule cannot enter the tightly packed lattice, and the amorphous region between the platelets is strengthened, so the toughness and environmental stress cracking resistance are improved. EVA is also commonly used to improve the compatibility of HDPE and other polymers, such as HDPE/ LDPE or HDPE/ PP blends with EVA, due to the improvement of the compatibility between the two, so that the impact toughness of HDPE increased. The incorporation of EVA into HDPE can be a flexible material for the manufacture of foam plastics.

Ethylene-vinyl acetate copolymer is prepared by copolymerization of ethylene and vinyl acetate. EVA obtained by copolymerization of different proportions of monomers has different VAc content and different uses. The production methods of ethylene vinyl acetate copolymer mainly include high pressure method, solution method and emulsion method. At present, the most widely used is the high pressure method.

1. High Pressure Process The high pressure bulk copolymerization process is similar to the production of LDPE. The copolymerization process may employ an autoclave reactor or a tubular reactor. In general, the kettle method is more suitable for the production of EVA, the production process of this method is similar to the high-pressure low-density polyethylene, the initiator used is also the same. The main difference is the need to add vinyl acetate monomer supply system and separation and recovery system. The specific preparation method is that ethylene, vinyl acetate, initiator and molecular weight regulator are added into a high-pressure reactor according to a certain ratio, and the polymerization reaction is carried out at 200~220 ℃ and under the pressure of 14.70~15.68 MPa, I .e. copolymers of different grades with vinyl acetate content of 10% ~ 50% (controlled as required) and molecular weight of 50000~500000 are prepared. After separation, refining, extrusion granulation and drying to obtain a granular product.
2. solution method medium content ethylene vinyl acetate copolymer can be produced by high pressure method, but most of them are produced by solution polymerization method under medium pressure. In the solution method, ethylene and VAc are polymerized in tert-butyl alcohol, aliphatic hydrocarbons and benzene which do not produce chain transfer, with peroxides and azo compounds as initiators at 5-7MPa and 30-150 ℃. The VAc content of the copolymer can be changed within a considerable range, generally above 35%.
3. emulsion polymerization is the opposite of bulk polymerization. It is a method for preparing EVA products with high VAc content, and its VAc content is 70% ~ 90%. The emulsion method is to add VAc and initiator K2 S2 0s or (NH4)2 S2 0a to the prepared emulsion medium (stabilizer, emulsifier, etc. are added to the aqueous medium) in a high-pressure reactor, introduce ethylene, and polymerize at less than 95 ℃ and 1 ~ lOMPa to obtain copolymer emulsion with VAc content of 70% ~ 90%.

• EVA resin has a wide range of applications, in which the production process of EVA has an impact on the performance and use of products. The content of VAc in EVA resin and the different uses of MFR are also different. EVA with low VAc content is similar to LDPE, soft and good impact strength, and is suitable for manufacturing heavy-duty packaging and composite materials. EVA with VAc content of 10% ~ 20% has good transparency and is suitable for agricultural film and shrink packaging film. EVA with more VAc content can be used as adhesives, coatings, coatings, and can also be made into EVA foam, electrical appliances, cable insulation and daily necessities. It can also be used for polymer modification to improve the flexibility and rigidity of plastics. The addition of EVA with a low degree of polymerization to the fuel oil can improve its cold flow characteristics. In other applications, the copolymers are made into finished products with no or very small amounts of additives or modifiers.
• The main uses of EVA resin are adhesives, blow molding, wire and cable manufacturing, film products, foam molded products, extrusion and co-extrusion, lamination, hot melt and injection molded products. EVA is also used for polymer modification to improve flexibility and rigidity, while low polymerization degree EVA can be added to fuel oil to improve its cold flow characteristics.

1. film film is one of the most important uses of EVA. The VAc content of film grade EVA resin is generally 126-15%, and the maximum is not more than 20%. Because the VAc content is too high, the resin viscosity is large, it is not suitable for blowing film. EVA resin with VAc content of 1 ~ 6-s% has moderate toughness and high transparency, which is suitable for making film and heavy packaging materials. Can be used as a single layer transparent film. VAc improved the heat sealing property of the film, increased the gloss of the film, and reduced the haze. EVA resin with VAc content of 5% ~ 7.5 is used for ice bag film. VAc can prevent the film from embrittlement at low temperature and keep the ice bag flexible in the cold and hot environment of pressing. EVA with VAc content of 10% ~ 20% can be used to make films for various purposes. The films have the advantages of high transparency, good impact toughness, good thermal stability, low air permeability, low shrinkage at low temperature, good printability, and physiological harmlessness. Packaging film is the largest market for EVA. EVA resin with VAc content of 10% ~ 12% and LLDPE resin are co-extruded to produce stretch film (EVA/ LLDPE/ EVA), which can replace shrink film and be used for container packaging and disposable strapping. EVA layer has excellent adhesive performance. EVA resin and barrier resin PVDC (polyvinylidene chloride) co-extruded film with VAc content of 9% ~ 15% are used for the packaging of fresh meat and processed beef and poultry. The role of the EVA layer is to ensure the heat sealing strength and heat shrinkage of the fresh meat bag. Compared with LDPE, EVA has a lower melting point; compared with LL-DPE, its shrinkage is more uniform. Therefore, EVA copolymer is the best choice material for this application. With a VAc content of 15% to 18%, the EVA film can also be used as a heat-fusion layer in coextruded films and for blending with homopolymers. The use of EVA, which belongs to the category of protection film, also includes extrusion and gluing on polyester, celluloid and PP films for cheese wrapping paper. EVA and gold-plated polyester film are co-extruded or laminated for bag wrapping instead of tinplate cans. Medical films and other uses with strict requirements.
2. Adhesive and coating hot melt adhesive is EVA the most important application of one, which is characterized by good mechanical properties and mechanical stability, high viscosity, particle size can be controlled, creep resistance and heat sealing between a good balance, a good wet viscosity and fast curing speed, difficult to bond the film matrix has special adhesion.
3. Molded and Extruded Articles EVA molded and extruded articles usually use copolymers with a VAc content of 9% to 18%, which has the advantage of flexibility and toughness. EVA can be extruded into high transparent hoses and tubes for blood transfusion, blood pressure, beverage and construction mortar, as well as hoses for vacuuming and water supply systems.
4. foam VAc content of 12% ~ 16% EVA manufacturing high rate, independent bubble type foam. This kind of foam plastic has heat insulation, heat preservation, shockproof, small compression deformation, good elasticity, good weather resistance and secondary processing, can be used in industry, construction industry, aquaculture, as insulation, shockproof, packaging materials. At present, it has been used for boat life buoyancy, locomotive carriages, etc., and has also begun to be used in building insulation. In the footwear industry, EVA with VAc content of 10% ~ 20% can be used as the main material alone or with LDPE, NR, BR, EPDM, CPE (chlorinated polyethylene) and used to make microporous soles.
5. mixing, composite materials EVA copolymer can withstand high doses of fillers, can be well blended with different organic or inorganic compounds, formulated into a variety of uses of composite materials or as a masterbatch carrier, so that it has a wider range of use. The main use of EVA composite materials is for wire and cable. A large amount of superconductors and carbon black for electrostatic dispersion, flame retardants for inhibiting the combustion of insulators, and other fillers and additives are added to EVA. And after steam and chemical vulcanization process or radiation treatment, can be made into insulation protection foam or sheath. When EVA is used as a color masterbatch carrier, the amount of dyes and additives (UV stabilizers) can be as high as 50% to 80%. The tolerance of EVA to the amount of additive is proportional to the VAc content in the resin. With the increase of VAc content, the absorption capacity of the additive is correspondingly improved, and the color masterbatch of high dosage additive can be prepared. EVA is also an excellent modifier, which can be blended with PE, PP and PVC to produce a series of plastic modified products with a wide range of applications. The addition of EVA improves the flexibility, toughness, stress cracking resistance and adhesive properties of the plastic base material.
6. Petroleum Crude Oil and Oil Additives When EVA with high VAc content is used as an additive for petroleum products, it can greatly reduce the freezing point of the fuel. EVA can be used as oil additives such as crude oil wax inhibitor and fluidity improver, which can reduce the freezing point of crude oil, thereby improving its low-temperature fluidity.
7. Other aspects One of the latest uses of EVA is for foundry production and powder metallurgy. When EVA is used as the veneer material on the inner surface of the casting mold, the sand can be completely cured without additional adhesive, and the pouring surface is smooth and easy to process. In powder metallurgy manufacturing, the alloy powder and EVA adhesive are mixed under vacuum or reduced pressure, which can improve the interface affinity of the alloy and improve the degree of free forming, so as to obtain powder metallurgy products without pinholes. EVA as a base material for the use of flame retardant low smoke resin. In high-tech application materials, EVA can also be used as a substrate resin for conductive materials, for heating elements, conductive films, elastic electrodes and electronic computer connectors.

The inner packaging of the product is a polyethylene film bag, and the outer packaging is a polypropylene woven bag, with a net weight of 25kg per bag. During storage and transportation, the warehouse or carriage should be kept dry, clean and well ventilated. Iron hooks are strictly prohibited during loading and unloading.

1. injection molding using general PE or PP injection equipment can be used. Because EVA has elasticity, it can be made into rubber-like products without the need to go through the vulcanization process, and coloring is easy, and the products are colorful. The lower limit of the molding temperature is to maintain a certain fluidity as the standard, and the upper limit temperature is to prevent the thermal decomposition of EVA. The thermal decomposition temperature is about 229~230 ℃, and in general, the material temperature is controlled at 170-200 ℃.
2. vacuum forming EVA vacuum forming products smooth and transparent. However, due to its poor thermal conductivity and low melting point, the cavity mold temperature should be low and the molding cycle should be long. Generally, the method of low temperature cooling mold can be used to form.
3. blow molding film using general blow molding equipment. Due to the low melting point of EVA, special consideration must be given to the cooling of the material. The traction force should be smaller, otherwise it will cause poor opening of the film products. In addition, it should be considered to add a slip agent.
4. foam molding foam molding should pay attention to adjust the amount of foaming agent. Its foamed products have the characteristics of elasticity, light weight, toughness and low shrinkage.

Ethylene-vinyl acetate copolymer, also known as EVA, is made of ethylene and vinyl acetate by copolymerization of a polymer.

1, properties:
elasticity and softness: EVA has excellent elasticity and softness, can maintain shape, and for bending and stretching have good resilience.
of 2, good weather resistance and chemical resistance: EVA has good weather resistance, can resist sunlight, oxidation, acid, alkali and other chemical substances, thereby extending its service life.
: 3, processability: EVA is easy to process into various shapes and sizes, including films, plates, particles, etc.
of 4, abrasion resistance and tear resistance: EVA has excellent abrasion resistance, can be used for a long time to maintain its physical properties, and has a high tear resistance. 5, chemical inert
: EVA with many solvents and chemicals compatible, with low permeability.

Uses:
plastic products 1, EVA can be used to make insoles, children's toys, beach sandals, goggles, etc., because of its good elasticity, softness and wear resistance.
: 2, film material: EVA can be used for solar panels packaging film, agricultural film, building waterproof film, etc.

Production method:
the general is ethylene and vinyl acetate and the right amount of polymerization initiator added to the reactor, in a certain temperature and pressure copolymerization reaction, in the reaction after the completion of the post-treatment measures, such as solvent extraction and drying, the preparation of EVA.

Safety information:
1, in the processing process, may produce toxic smoke and gas, should be in a well ventilated environment operation. 2, in contact with the skin or eyes, should be promptly with plenty of water rinse, and consult a doctor.