Ethylene-vinyl alcohol copolymer

Ethylene-vinyl alcohol copolymer (EVOH): Combining the processability of ethylene polymer with the barrier effect of vinyl alcohol polymer, ethylene-vinyl alcohol copolymer not only exhibits excellent processing properties, but also exhibits excellent blocking effects on gases, odors, fragrances, solvents, etc. Multi-layer containers containing EVOH barriers are fully reusable due to their thermal stability combined with ethylene. It is these characteristics that enable plastic containers containing EVOH barrier layers to replace many glass and metal containers in food packaging. (1) Chemistry and Properties Among the polymers available today, polyvinyl alcohol (PVOH) has the lowest gas permeability. However, PVOH is water-soluble and difficult to process. EVOH copolymer is made like this: First, ethylene and vinyl acetate are copolymerized, and then the copolymer is hydrolyzed to obtain ethylene-vinyl alcohol. Therefore, a high degree of barrier effect is still retained, and there is a significant improvement in moisture resistance and processing properties. In terms of nature, EVOH copolymer is highly crystalline, and its properties mainly depend on the relative concentration of its comonomers. Generally speaking, as ethylene content increases, gas barrier properties decrease, moisture resistance improves, and the resin becomes easier to process. The most notable feature of EVOH resin is its gas barrier effect. It is used in packaging structures to improve flavor and quality retention by preventing the penetration of oxygen. In the use of inflatable packaging technology, 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 moisture is adsorbed, the gas barrier properties will be affected. However, the moisture content in the barrier layer can be carefully controlled, and this can be accomplished by using multi-layer technology to wrap the EVOH resin layer with a strong moisture barrier resin such as polyolefin. (2) Oil-resistant EVOH resin also has strong oil resistance and organic solvent resistance. The percent weight gain after 1 year of immersion in various solvents and oils at 68°F is: For solvents such as cyclohexane, xylene, petroleum ether, benzene and propylene, it is 0%, for ethylene glycol it is 2.3%, and for methanol it is 12. 2%, for salad oil it is 0. 1%. (3) Thermal/mechanical properties EVOH resin has high mechanical strength, elasticity, surface hardness, wear resistance and weather resistance, and has strong antistatic properties. EVOH film has high gloss and low haze, making it highly transparent. EVOH resin is the resin with the highest thermal stability among all commercial strong barrier resins. This property allows the waste materials generated during processing to be regenerated and reused. The recycled materials contain up to 20% EVOH. (4) Processing There are three basic methods for using EVOH to provide interlayers in multi-layer structures. They are: Co-extruded structure. EVOH resin is combined with polyolefin or polyphenolamine to form a framework. EVOH films are laminated to other substrates or coated with other materials. Use EVOH resin as a coating for various substrates or single-layer containers. It can be easily processed on conventional manufacturing equipment without requiring special changes. Using commercial equipment, EVOH resin is suitable for the following processes: Single or multi-layer film extrusion ； Sheet and profile co-extrusion ； Co-extrusion blow molding ； Co-extrusion coating ； Lamination (or stacking) and injection molding. Secondary processing such as thermoforming, vacuum forming and printing with EVOH resin structures or EVOH films can be easily performed. Like other polymers, EVOH resins can be modified by superheating. Coating techniques involving multi-layer coatings or co-extrusion coatings can also be used to produce multi-layer structures, with the resulting structures closely resembling co-extrusion structures. EVOH resin spraying, dipping or roller coating methods can be used. To produce containers for carbonated beverages or to block solvents, flavors or odors. EVOH resins have poor adhesion to most polymers. To overcome this difficulty, specially designed bonding resins or "joining resins" are used. With the exception of nylon, EVOH resin can adhere well to nylon without the use of adhesive resin. (5) New Developments With the growth of rigid, high-barrier plastic packaging, new performance requirements have been put forward for EVOH resins. To meet these needs, EVOH suppliers provide certain brands of products, such as J102 (EVAL Company of the United States - EVALCA) and ST series products of Japanese Goshei Company. These products offer improved processability and wider molding range. Other products, such as US EVAL's F100 and E151, have also been developed that have better viscosities and are better matched to typical polyolefins used in rigid containers. In the field of plastic recycling, EVOH resin has even more advantages. Used high-density polyethylene milk bottles and multi-layer bottles (containing EVOH resin) are blended to produce non-food containers. (6) Application Barrier layer structures containing EVOH resins are used in all hard and flexible packaging and in all types of food processing including aseptic, hot injection and pressure cooking. Products packaged with EVOH-containing materials include: Condiments (soy sauce), tomato sauces, juices, edible batters, meat products, cheese products and processed fruits. Non-food applications include solvents, chemicals and pharmaceutical-related product packaging. Manufacturers of vehicle fuel tanks, fuel lines and air conditioning equipment are evaluating whether to use EVOH structures to reduce hydrocarbon and/or Freon emissions.

Mainly the comparison of process route technology! Industrialization maturity and production scale!