Short answer
EVOH blocks oxygen via dense hydrogen bonding in its crystalline regions; but it is hydrophilic, and above ~60% RH its barrier collapses, so it must be protected between hydrophobic layers such as PE.
Why EVOH blocks oxygen so well
- Ethylene units give processability; vinyl-alcohol units form dense hydrogen bonds;
- Dense chain packing leaves little path for oxygen;
- Dry-state OTR can be ~1000x lower than typical PE.
The weakness: humidity
| Relative humidity | Oxygen barrier |
|---|---|
| Dry (0-60%) | Excellent |
| High (80%+) | Drops sharply (10x+) |
High-moisture foods release water internally, weakening EVOH — hence the sandwich structure.
Typical coextruded structure
PE / tie / EVOH / tie / PE
Note for molded-fiber lamination
EVOH is often the inner barrier layer coextruded before lamination. For MAP, confirm moisture management of the whole structure; a single EVOH layer is unsuitable for wet/fresh applications.
Data & limits
OTR varies strongly with EVOH ethylene content, thickness and humidity. Provide application humidity and target shelf life; DNW engineers help design the layer stack.