Ethylene-vinyl acetate copolymer (EVA) is a general-purpose high molecular polymer with the molecular formula (C2H4)x.(C4H6O2)y. It is flammable and has a non-irritating burning odor.
Basic Information
| Features | introduce |
|---|---|
| Water resistance | Closed cell structure, no water absorption, moisture proof and good water resistance. |
| Corrosion resistance | Resistant to corrosion from seawater, grease, acid, alkali and other chemicals, antibacterial, non-toxic, odorless and pollution-free. |
| Processability | There are no joints and it is easy to process by heat pressing, cutting, gluing, laminating, etc. |
| Anti-vibration | It has high resilience and tensile strength, high toughness, and good shockproof and cushioning properties. |
| Thermal insulation | It has excellent thermal insulation , heat preservation, cold protection and low temperature performance, and can withstand severe cold and exposure. |
| Sound insulation | Closed cells, good sound insulation effect. |
Common features
When the vinyl acetate content in EVA is less than 20%, it can be used as plastic. EVA has good low temperature resistance and its thermal decomposition temperature is low, about 230°C. As the molecular weight increases, the softening point of EVA rises, the processability and surface gloss of the plastic parts decrease, but the strength increases, and the impact toughness and environmental stress cracking resistance improve. EVA’s chemical resistance and oil resistance are slightly worse than PE (polyethylene) and PVC (polyvinyl chloride), and the change is more obvious with the increase of vinyl acetate content.
Compared with PE, EVA has improved performance mainly in terms of elasticity, flexibility, glossiness, air permeability, etc. In addition, its resistance to environmental stress cracking has been improved, and its tolerance to fillers has been increased. The method of adding more reinforcing fillers can be used to avoid or reduce the decline in EVA’s mechanical properties compared with PE. EVA can also be modified to obtain new applications. Its modification can be considered from two aspects: one is to use EVA as the backbone for grafting other monomers; the other is to partially alcoholize EVA.
Hazardous characteristics
Powder and air can form explosive mixtures. When reaching a certain concentration, it will explode when encountering sparks. Heating and decomposition will produce flammable gas.
Preparation method
(1) High-pressure method: Ethylene, vinyl acetate, organic peroxide or azo compound or oxygen and other initiators and suitable molecular weight regulators are added into a high-pressure reactor according to the ratio. The polymerization reaction is carried out at a pressure of 1000 kg/cm² and a temperature above 200°C. A copolymer with a vinyl acetate content of 10-40% and a molecular weight of 20,000-500,000 is obtained.
(2) Emulsion method: In a high-pressure reaction chamber, vinyl acetate and K2S2O8 or (NH4) S2O8 initiator are first added to the prepared emulsion reaction medium, and then ethylene is added. Polymerization is carried out at 10-95°C and 10-100 kg/cm² pressure to obtain a copolymer latex with a vinyl acetate content of 70-95%.
(3) Solution method: At an ethylene pressure of 65 bar and 150°C, using benzene as solvent and di-tert-butyl peroxide as initiator, ethylene and vinyl acetate are copolymerized for about 3 hours. If lauroyl peroxide is used as initiator, the reaction can be carried out at an ethylene pressure of 50 bar and 82°C, or it can be carried out in a tubular continuous polymerization at 100-300 atmospheres and 200-250°C. If the reaction is carried out at 250 atmospheres and 220°C with a residence time of 80 seconds, polyethylene-vinyl acetate with a vinyl acetate content of 30-40% and a molecular weight of 2000 can be obtained.
Molding method
The molding method of ethylene-vinyl acetate copolymer can adopt the molding method and equipment of general thermoplastics, and the processing temperature is 20 to 30°C lower than that of LDPE.
Injection molding
Due to its elasticity, it can be made into rubber-like film products without going through vulcanization and other processes. Ethylene-vinyl acetate copolymer is easy to color, and the products are brightly colored. The lower limit of the molding temperature is based on maintaining a certain fluidity, and the upper limit is to prevent the thermal decomposition of ethylene-vinyl acetate copolymer. The material temperature is generally controlled at 170-200℃.
Vacuum forming
The vacuum-formed products of ethylene-vinyl acetate copolymer are smooth and transparent. The molding equipment used is similar to that of LPPE.
Extrusion, calendering
Similar to the equipment used for PE and PVC, calendering glue coating, extrusion coating and multi-layer co-extrusion compounding can be adopted.
Extrusion Blow Molding
During extrusion blow molding, special consideration must be given to the cooling of the material, and the traction force should be lighter, otherwise the opening will be poor, and a lubricant should be added if necessary.
Foam molding
The expansion rate of EVA foam can be effectively controlled by adjusting the amount of foaming agent. The scraps can be recycled and no vulcanization is required. EVA foam has the characteristics of good elasticity, light weight, strong toughness and low shrinkage.
Handling and attention
Hazardous combustion products: Carbon monoxide, carbon dioxide.
Fire extinguishing methods
Firefighters must wear gas masks and full-body fire suits and extinguish fires in the upwind direction. Fire extinguishing agents: mist water, foam, dry powder, carbon dioxide, sand and soil.
Emergency treatment
Isolate the leaked contaminated area and restrict access. Cut off the fire source. It is recommended that emergency response personnel wear dust masks (full-face masks) and protective clothing. Avoid raising dust, sweep it up carefully, put it in a bag and transfer it to a safe place. If there is a large amount of leakage, collect and recycle it or transport it to a waste disposal site for disposal.
Operation Note
Operate in a closed environment and provide good natural ventilation. Operators must receive special training and strictly abide by the operating procedures. It is recommended that operators wear self-priming filter dust masks, chemical safety glasses, anti-poison penetration work clothes, and rubber gloves. Stay away from fire and heat sources. Smoking is strictly prohibited in the workplace. Use explosion-proof ventilation systems and equipment. Avoid generating dust. Avoid contact with oxidants and alkalis. Load and unload gently during transportation to prevent damage to packaging and containers. Equip with appropriate types and quantities of fire-fighting equipment and leakage emergency treatment equipment. Empty containers may contain harmful substances.
Storage Notes
Store in a cool, ventilated warehouse. Keep away from fire and heat sources. Store separately from oxidants and alkalis and avoid mixing. Equip with appropriate types and quantities of fire-fighting equipment. The storage area should be equipped with appropriate materials to contain leaks.
Main Application
Overview
EVA resin is an ethylene-vinyl acetate copolymer, and the general vinyl acetate (VA) content is 5% to 40%. Compared with polyethylene, EVA has introduced vinyl acetate monomer into the molecular chain, which reduces the high crystallinity and improves flexibility, impact resistance, filler compatibility and heat sealing performance. It is widely used in foaming shoe materials, functional greenhouse films, packaging films, hot melt adhesives, wires and cables, and toys. In general, the performance of EVA resin mainly depends on the content of vinyl acetate in the molecular chain.
Oilfield
As a crude oil paraffin inhibitor and flow point improver: Since the oil-soluble ethylene-vinyl acetate copolymer has chain links similar to the structure of paraffin, it can form a network structure throughout the crude oil at a very low concentration, causing paraffin to precipitate under the network structure and separate from each other, making it difficult to aggregate and grow, and not easy to deposit on the pipe wall, thereby reducing the freezing point of the crude oil. For example, adding ethylene-vinyl acetate copolymer with a vinyl acetate content of 18% and a molecular weight of 12,000 to crude oil in Texas, the freezing point can be reduced from 25°F to -5°F when used at 0.05%. When using it, mix it with an adductor, etc., make it into granular, flaky or honeycomb shapes, and lower it into the wellbore at the oil layer, and slowly dissolve in the oil;
Used for selective water plugging in oil wells: Thermoplastic ethylene-vinyl acetate copolymer oil solution can be used for water plugging in deep wells with high temperature and large amount of water. In the oil layer, ethylene-vinyl acetate copolymer dissolves in the oil and can flow back with the oil; but in the water layer, it is insoluble in water and precipitates highly viscous substances when it meets water, which creates great resistance to water and blocks the water flow channel;
Added to thickened water fracturing fluid as a fluid loss reducer.
Foam shoe material
Shoe materials are the main application field of EVA resin in China. In the EVA resin used in shoe materials, the vinyl acetate content is generally 15% to 22%. Since EVA resin blended foam products have the properties of softness, good elasticity, and chemical corrosion resistance, they are widely used in the soles and interior materials of mid-to-high-end tourist shoes, hiking shoes, slippers, and sandals. In addition, this material is also used in the fields of sound insulation boards, gymnastics mats, and sealing materials.
Film
The main purpose of EVA film is to produce functional greenhouse film. Functional greenhouse film has high weather resistance, anti- fog and heat preservation properties. Since polyethylene is not polar, even if a certain amount of anti-fog agent is added, its anti-fog performance can only last for about 2 months; while greenhouse film made by adding a certain amount of EVA resin not only has a higher light transmittance, but also has greatly improved anti-fog performance, which can generally exceed 4 months. In addition, EVA can also be used to produce packaging film, medical film, laminated film, casting film, etc.
Wire and Cable
With the continuous development of computer and network engineering, people are increasingly using halogen-free flame-retardant cables and silane cross-linked cables for the sake of computer room safety. Since EVA resin has good filler tolerance and cross-linkability, it is widely used in halogen-free flame-retardant cables, semiconductor shielded cables and two-step silane cross-linked cables. In addition, EVA resin is also used to make sheaths for some special cables. The vinyl acetate content of EVA resin used in wires and cables is generally 12% to 24%.
Toy
EVA resin is also widely used in toys, such as children’s wheels, seat cushions, etc.
Hot Melt Adhesive
Hot melt adhesive with EVA resin as the main component does not contain solvents, does not pollute the environment and is highly safe, making it very suitable for automated assembly line production. Therefore, it is widely used in book wireless binding, furniture edge banding, automobile and home appliance assembly, shoemaking, carpet coating and metal anti-corrosion coating.
It can be used to make refrigerator ducts, gas pipes, civil engineering panels, containers and daily necessities, as well as packaging films, gaskets, medical equipment, and can also be used as hot-melt adhesives, cable insulation layers, etc.
EVA emulsion
EVA emulsion is the abbreviation of vinyl acetate -ethylene copolymer emulsion. It is a high molecular emulsion made by copolymerizing vinyl acetate and ethylene monomers as basic raw materials with other auxiliary materials through emulsion polymerization method.
EVA emulsion is mainly used in adhesives, coatings, cement modifiers and paper processing, and has many excellent properties.
EVA emulsion has permanent flexibility. EVA emulsion can be regarded as an internal plasticization product of polyvinyl acetate emulsion. Because it introduces ethylene molecular chains into polyvinyl acetate molecules, the acetyl group becomes discontinuous, the rotational freedom of the polymer chain is increased, the space hindrance is small, the polymer main chain becomes soft, and no plasticizer migration occurs, ensuring the permanent softness of the product.
EVA emulsion has good acid and alkali resistance. EVA emulsion can maintain stable performance in the presence of weak acid and weak base, so it will not demulsify no matter it is mixed with weak acid or weak base, and the product has a wide range of applications.
EVA emulsion is resistant to UV aging. Since EVA emulsion uses ethylene as the internal plasticizer of the copolymer, the EVA polymer has internal plasticization, and the plasticizer will not migrate, thus avoiding the aging of polymer performance. Therefore, not only is EVA emulsion very stable to UV rays, but this feature can also be maintained after the EVA emulsion forms a film.
EVA emulsion has good miscibility. EVA emulsion can be mixed with most additives, such as dispersants, wetting agents, antifreeze agents, defoaming agents, preservatives, flame retardants, etc., so it can meet various needs; EVA emulsion can be mixed with many pigments and fillers without coagulation; EVA emulsion can be directly mixed with many low-molecular and high-molecular water-soluble polymers, such as polyvinyl alcohol aqueous solution, polyethylene glycol aqueous solution, starch or modified starch gelatinized liquid, sodium polyacrylate aqueous solution, polymaleic acid aqueous solution, polyoxyethylene aqueous solution, urea-formaldehyde, phenolic acid aqueous solution, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose aqueous solution, etc.; EVA emulsion can be directly mixed with many other high-molecular polymer emulsions, such as polyvinyl acetate emulsion, polyacrylate emulsion; EVA emulsion can be mixed with aldehydes, esters, ketones, organic acids, polyols, higher alcohols,Direct mixing of halogenated hydrocarbons, aromatic hydrocarbons, etc., such as formaldehyde, glyoxal, dibutyl phthalate, dioctyl phthalate, acetic acid, carbon tetrachloride, chloroform, benzene, toluene, xylene, octanol, ethylene glycol, propylene glycol, ethyl acetate, butyl acetate, etc.
EVA emulsion has good film-forming properties. Emulsion adhesives can only form a transparent film at a certain temperature, which is called the minimum film-forming temperature. The minimum film-forming temperature of EVA is generally lower than 5°C, so it can form a good film, and the film has good barrier properties against water droplets.
EVA emulsion has good adhesion. It has a good bonding effect on fiber, wood, paper, plastic film, aluminum foil, cement, ceramics and other products.
According to the waterproofness of EVA emulsion polymer, it can be divided into two categories: general-purpose and waterproof. General-purpose EVA polymers have good rigidity and high bonding strength, but poor water resistance; waterproof EVA polymers have good flexibility and water resistance, but low bonding strength. According to EVA application performance, copolymer composition and copolymer third monomer type, EVA emulsion can be divided into two categories: adhesive and textile. Adhesive EVA is mostly used as a general-purpose adhesive, while textile adhesive is mostly used as an adhesive for textile fibers, but there is no absolute boundary between the two.
Since EVA emulsion has many excellent properties, it has a wide range of uses in practical applications.
EVA emulsion is widely used as the base material of adhesives. EVA emulsion has excellent mechanical properties, small average particle size of emulsion particles, a good balance between creep resistance and heat sealing, good wet adhesion and fast curing speed. EVA emulsion has a wide range of bonding properties. In addition to bonding wood, leather, fabric, paper, cement, concrete, aluminum foil, galvanized steel and other materials, it can also be used as a pressure-sensitive adhesive and heat-sealing adhesive, and it has unique bonding properties for some difficult-to-bond materials such as polyethylene, polypropylene, polyvinyl chloride, polyester and other films.
EVA emulsion can be used as the base material of coating. The coating made of polyvinyl acetate emulsion, acrylic emulsion, EVA emulsion, styrene-butadiene emulsion, propylbenzene emulsion, acetobenzene emulsion etc. as the base material is collectively referred to as latex paint. EVA latex paint can be used as interior and exterior wall coating, roof waterproof coating, fireproof coating, rust-proof coating. EVA latex paint film has good foaming resistance, aging resistance and is not easy to crack. It has good adhesion with various substrates, is safe and non-toxic, and is easy to use. EVA latex paint can not only be applied on wood, masonry and concrete, but also on metal, glass, paper, and fabric surfaces. It also has good affinity with paint and can be brushed on its surface.
EVA emulsion can be used in paper processing. With the development of synthetic polymer technology, many polymer substances play a great role in paper processing, especially some synthetic polymer emulsions are more superior in paper processing, and EVA emulsion is one of them. EVA emulsion is mainly used for paper impregnation, paper coating and pulp addition in paper processing. Its characteristics are that it can glaze a variety of papers, increase the dry and wet strength, toughness and glossiness of paper, improve color stability, reduce ink printing consumption, and improve paper grade. As a pulp additive, various types of non-asbestos gaskets can be made. EVA emulsion can also be used in special paper processing, such as using dry puffing papermaking to make disposable napkins, facial towels, diapers, sanitary napkins, etc.
EVA emulsion can be used as cement modifier, and cement is one of the most widely used materials in construction projects. However, pure cement products have the disadvantages of easy cracking and poor water resistance, impact resistance, and acid resistance, which to a certain extent affect the practical effect of cement. Since the 1920s, people have been committed to the modification of cement. With the deepening of research, people have found that many synthetic latexes have good effects on cement modification, such as polyvinyl acetate emulsion, acrylic emulsion, styrene butadiene and toluene emulsion, EVA emulsion, etc. Among them, EVA emulsion has good water resistance, acid and alkali resistance, and weather resistance, and its price is cheaper than similar products. Therefore, it is widely used in civil engineering as a new material. Considering environmental protection, EVA redispersible latex powder has gradually appeared on the market, and gradually replaced EVA emulsion in cement modifiers, becoming the main product of cement modifiers.
EVA Models
EVA is ethylene-vinyl acetate copolymer, which is made by copolymerization of ethylene (E) and vinyl acetate (VA). Its English name is: Ethylene Vinyl Acetate, referred to as EVA, or E/VAC. Generally, the content of vinyl acetate (VA) is 5% to 40%. Compared with polyethylene, EVA has reduced crystallinity and improved flexibility, impact resistance, filler compatibility and heat sealing performance due to the introduction of vinyl acetate monomer into the molecular chain. Generally speaking, the performance of EVA resin mainly depends on the content of vinyl acetate in the molecular chain. Because the proportion of the constituent components can be adjusted to meet different application needs, the higher the content of vinyl acetate (VA content), the higher its transparency, softness and toughness will be.
The polymerization methods include high-pressure bulk polymerization (for plastics), solution polymerization (PVC processing aid), emulsion polymerization (adhesive), and suspension polymerization. Emulsion polymerization is used for materials with a vinyl acetate (VA) content higher than 30%, and high-pressure bulk polymerization is used for materials with a low vinyl acetate content.
EVA classification
Ethylene- vinyl acetate copolymer is the most important product among ethylene copolymers, and is generally referred to as EVA abroad. However, in China, people classify ethylene-vinyl acetate copolymer into EVA resin, EVA rubber and EVA emulsion according to the different vinyl acetate contents. Products with vinyl acetate content less than 40% are EVA resins; products with vinyl acetate content of 40% to 70% are very flexible and elastic, and people sometimes call EVA resins in this content range EVA rubber; products with vinyl acetate content in the range of 70% to 95% are usually in an emulsion state, called EVA emulsion. EVA emulsion has a milky white or slightly yellow appearance.
Postscript
With the improvement of people’s living standards and the strengthening of environmental protection awareness, EVA emulsion is gaining more and more market share. Although the two sets of china imported production equipment have undergone technical transformation during the production process, the actual output has been greatly increased (today’s china EVA emulsion annual output is between 45,000 and 50,000 tons), there is still a large gap compared with the actual demand, which can only be supplemented by imports.
