Meaning
Ethylene vinyl alcohol is a copolymer formed from the polymerization of ethylene and vinyl alcohol. This thermoplastic resin prevents the passage of oxygen and other gases through its molecular chain while remaining resistant to oils and organic solvents. Production involves a hydrolyzation process where the vinyl acetate component is transformed into vinyl alcohol units.
The material density and gas transmission rate depend directly upon the ethylene content of the polymer chain.
Barrier Performance
Oxygen transmission represents the primary metric governed by this polymer in food packaging and fuel line applications. Molecules of gas struggle to migrate through the crystalline structure of the resin, providing a protection layer that maintains freshness or internal pressure. Extrusion processes often place this layer between outer protective skins of polyolefins to guard against moisture sensitivity.
High humidity environments cause the material to absorb water, which drops the barrier effectiveness during operation.
Processing Mechanics
Moulding teams manage the thermal stability of the resin to prevent degradation in the feed throat or nozzle. Temperatures exceeding the recommended limit trigger internal crosslinking, which creates black specs or gels in the finished part. Regrind usage requires strict control because repeated heating cycles diminish the chemical integrity of the chain.
Virgin material offers consistent viscosity for thin wall applications, whereas high levels of regrind cause fluctuations in the flow front and wall thickness.
Cost Economics
Procurement departments weigh the high unit price of the resin against the shelf life benefits it offers for perishable products. Downsizing the thickness of the barrier layer reduces individual part expenditure but creates a risk of leakage if the film experiences mechanical stress. Packaging designs balance the cost of these thinner constructions by adding support from cheaper structural polymers like polypropylene.
Precise dosage control during the coextrusion phase eliminates waste, ensuring the performance per unit remains stable across a long production run.
