Ethylene is a hydrocarbon with the formula C₂H₄or H₂C=CH₂. It is a colorless flammable gas with a faint "sweet and musky" odor when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds), and the simplest unsaturated hydrocarbon after acetylene (C₂H₂).
Ethylene vinyl alcohol (EVOH) is a formal copolymer of ethylene and vinyl alcohol. The copolymer is prepared by polymerization of ethylene and vinyl acetate to give the ethylene vinyl acetate (EVA) copolymer followed by hydrolysis. EVOH copolymer is defined by the mole % ethylene content: lower ethylene content grades have higher barrier properties; higher ethylene content grades have lower temperatures for extrusion.
The plastic resin is commonly used as an oxygen barrier in food packaging. It is better than other plastics at keeping air out and flavors in, is highly transparent, weather resistant, oil and solvent resistant, flexible, moldable, recyclable, and even printable. It is also used as a hydrocarbon barrier in plastic fuel tanks.
The production of EVOH is a two-step process of polymerization and saponification. EVOH is produced by the controlled hydrolysis of ethylene vinyl acetate copolymer.
The highly polar OH groups increase the intermolecular mobility. The polymer randomly distributes ethylene and vinyl alcohol units. The ratio of ethylene to vinyl alcohol determines the end product characteristics. The lowest ethylene or the highest vinyl alcohol content is used to get high barrier properties, whereas the highest ethylene content or the lowest vinyl alcohol leads to better flexibility.
EVOH copolymers are produced by first co-polymerising ethylene with vinyl acetate and then hydrolyzing the copolymer to form ethylene vinyl alcohol.
Ethylene and vinyl acetate are polymerized using an initiator/activator complex and ethylene-vinyl acetate copolymer (EVAc) is saponified to ethylene vinyl alcohol copolymer.
For a co-extrusion process two or more materials have to be extruded through a single die with two or more orifices arranged in a way, that the hot thermoplastic masses merge and weld together into a laminar structure before chilling. Each material is fed to the die from a separate extruder, but the orifices may be arranged so that each extruder supplies two or more plies of the same material. Co-extrusion can be employed in film blowing, free film extrusion and extrusion coating processes. The advantage of co-extrusion is that each ply of the laminate imparts a special desired characteristic property, such as stiffness, heat-sealability, impermeability or resistance to some environment, all of these properties would be impossible to attain with any single material.
EVOH with different kind of Ethylene content can be applied in various barrier products by the fabrication process method of blown or cast co-extrusion, co-extrusion lamination, co-extrusion coating to form bottles, sheet, sheet (thermoforming), films, cast films, pipes or fibres.
EVOH is used in a liquid embolic system in interventional radiology. Dissolved in dimethyl sulfoxide (DMSO) and mixed with a radiopaque substance; ethylene vinyl alcohol copolymer is used to embolize blood vessels.
The global total capacity to make EVOH is 132000 metric tonnes per annum .
The United States is the world’s largest EVOH resin producer with a capacity of 60,000 metric tonnes per annum, accounting for around 45.45% of the world total. Belgium comes next with a capacity of 24000 metric tonnes , accounting for around 18.18%.
Global demand trend
EVOH resin demand is steadily expanding, particularly for food packaging applications and for automobile fuel tanks.
The increase in EVOH resin demand was earlier centered primarily in industrialized nations, such as Japan and the U.S, as well as in Europe. Increase in demand is expected in emerging markets such as South America as well as China and other Asian markets.
EVOH resin processing methods adopted by extrusion companies:
· Monolayer film extrusion (blown or cast)
· Co-extruded film extrusion (blown or cast)
· Co-extrusion blow molding
· Co-extrusion coating
· Injection molding
Producers and Suppliers of EVOH in India
· Graphic Innovations
· L.D International
· Plast Alloys India Ltd
· V P Traders
· Texas Oil Corp
· R S Overseas Pvt. Ltd.