Why is EVOH the highest barrier material ?
Ethylene Vinyl Alcohol, commonly abbreviated EVOH, is a formal copolymer of ethylene and vinyl alcohol.
EVOH has always been used as high barrier material. The film types of this material in addition to non-tensile type, there are bidirectional tensile type, aluminum evaporation type, and adhesive coating type, etc., bidirectional tensile type and heat resistant type for aseptic packaging products. EVOH is characterized by excellent barrier property for gas and excellent processing property, and excellent transparency, gloss, mechanical strength, elasticity, abrasion resistance, cold resistance and surface strength.
(1) Chemical Properties
Polyvinyl alcohol (PVA) has the lowest gas permeability of any polymer available today. However, PVA is water-soluble and difficult to process.
EVOH preparation method: first, ethylene and vinyl acetate copolymer were copolymerized, and then the copolymer was hydrolyzed to obtain ethylene – vinyl alcohol. Therefore, it still retained the high barrier function, but in the moistureproof and the processing performance aspect has the obvious improvement.
In terms of properties, EVOH copolymer is highly crystalline, and its properties mainly depend on the relative concentration of its comonomer. Generally speaking, when ethylene content increases, gas barrier property decreases, moisture resistance improves, and resin is easier to process. The most prominent feature of EVOH resin is its barrier to gases. It is used in packaging structures to improve retention of fragrance and quality by preventing oxygen infiltration. In the use of gas-filled packaging, EVOH resin effectively retains the carbon dioxide or nitrogen used to protect the product.
Due to the presence of hydroxyl groups in the molecular structure of EVOH resin, EVOH resin is hydrophilic and hygroscopic. When adsorbing moisture, the barrier property of gas will be affected. However, the moisture content in the barrier layer can be carefully controlled, which can be achieved by wrapping EVOH resin layers in a multi-layer technique using strong barrier resins such as polyolefin.
(2) Oil Resistance
EVOH resin also has strong resistance to oil and organic solvents. After immersion in various solvents and oils at 68°F for 1 year, the percentage weight gain was 0% for solvents such as p-cyclohexane, xylene, petroleum ether, benzene, and acetone, 2.3% for ethylene glycol, 12.2% for methanol, and 0.1% for salad oil.
(3) Thermal/mechanical Properties
EVOH resin has high mechanical strength, elasticity, surface hardness, wear resistance and weather resistance, and has a strong antistatic property.
EVOH films are highly transparent due to their high gloss and low haze.
EVOH resin is the highest thermal stability resin among all commercial strong barrier resins. This property enables the processing of waste products can be recycled and reused, the raw materials contain up to 20% of EVOH.
There are three basic ways to provide compartments using EVOH in a multilayered structure. They are:
- Coextrusion structure: EVOH resin binds to polyolefin or polyphenolamine to form a framework.
- EVOH films are laminated to other substrates or coated with other materials.
- Resin is used as coating for various substrates or single-layer containers.
It can be easily processed on traditional manufacturing equipment without special changes.
Using commercial equipment, EVOH resin is suitable for the following processing: single or multi-layer thin film extrusion; Sheet and profile co-extruded; Co-extrusion blow molding; Coextruded coating; Lamination (or lamination) and injection molding.
Secondary processing such as heat forming, vacuum forming and printing of EVOH resin frames or EVOH films is easy. Like other polymers, EVOH resins can be modified by overheating.
Coating techniques including multilayer coatings or coextruded coatings can also be used to produce multilayer structures, resulting in structures very similar to coextruded structures.
EVOH resin can be used for spraying, immersion or roller coating methods. The production of carbonated beverage containers or to achieve the purpose of blocking solvents, spices or smell.
EVOH resins have poor adhesion to most polymers, and to overcome this difficulty a specially designed bonding resin or “bonding resin” is required. Except for nylon, EVOH resin can stick to nylon well without the use of adhesive resin.
(5) New development
With the increase of rigid and high barrier plastic packaging, new performance requirements for EVOH resin are put forward. To meet these requirements EVOH suppliers offer certain brands such as J102(EVAL -EVALCA, USA) and Goshei, Japan’s ST series. These products improve machinability and a wider range of molding. Other products, such as EVAL inc. ‘s F100 and E151, have been developed for better viscosity and better match the polyolefin typically used in rigid containers.
At the same time of accelerating the research of EVOH composite film, the tensile orientation of EVOH is also being studied abroad. The barrier property of the new EVOH film to gas is 3 times that of the existing high performance non-tensile EVOH film.
In addition, EVOH can also be used as a barrier material coated on other synthetic resin packaging materials to enhance the barrier performance.
- Non-food applications include solvents, chemicals, air conditioner components, gasoline drum lining, electronic components, and packaging of medically related products.
- In the field of packaging, EVOH is made into a composite film as a intermediate barrier layer, which is used in all hard and soft packaging. In the food industry for aseptic packaging, hot cans and cooking bags, packaging dairy products, meat, canned fruit juices and condiments; Plastic containers of EVOH can completely replace glass and metal containersIn terms of food packaging. Many domestic aquatic products companies export seafood using five layers of PE/EVOH/PA/EVOH/PE co-extrusion membrane vacuum packaging.
- EVOH products can not only be used in film production, but also can be widely used in soft packaging of cosmetics, floor heating pipes, jelly cups and pesticide bottles, etc. As a non-toxic and environmentally friendly material, EVOH can not only improve people’s life quality, but also play an important role in environmental protection.
EVOH is currently produced by Changchun Group of Taiwan province, Synthetic Chemistry of Japan and KURARAY of Japan. Our company can supply you all grades of EVOH with high quality and competitive price. Sample is available, if you have any need, please feel free to contact me anytime.