The barrier polymers used in multilayer bottles and containers have very low gas permeability values compared to other commercial polymers such as PE (polyethylene) and PP (polypropylene).
They do not have physical properties that allow them to use as packaging produced from a single material, or are too expensive to use alone.
For these two main reasons above, barrier polymers are used as thin layers in multilayer packaging. Thermoform (heat forming) or coextrusion — they may be manufactured by blowing (inflating) molding methods. Their main task is to reduce the oxygen permeability of the packaging of oxygen-sensitive products. Some of the barrier polymers are also good for chemicals. They can also be used as solvent barriers and barriers that prevent aroma loss in food.
EVOH (ethylene vinyl alcohol copolymer), PA (polyamide) and PVDC (polyvinyl dichloride) polymers are often used to increase barrier properties in rigid plastic packaging.
Areas Used in Rigid Plastic Packaging
- Ketchup Bottles
- Mayonnaise Bottles
EVOH (Ethylene Vinyl Alcohol Copolymer)
EVOH polyvinyl is based on alcohol. Polyvinyl alcohol has very low oxygen permeability when pure. However, this polymer can be easily soluble in water. Therefore, it is not enough material alone to produce hard plastic packaging. By combining with ethylene, vinyl alcohol becomes processable by creating copolymer, thus increasing its resistance to water vapor. However, as the ethylene content increases, so does gas permeability. For this reason, in the rigid plastic packaging industry, copolymers with an ethylene amount of 30% — 40 are preferred.
EVOH (ethylene vinyl alcohol copolymer) is one of the most widely used oxygen barrier polymers in multi-layer PE (polyethylene) and PP (polypropylene) rigid plastic packaging. EVOH can also be used as a solvent barrier in many multilayer plastics.
PA (Polyamide / Nylon)
Polyamides, known as Nylon 6 and Nylon 66, are often used as gas barriers in flexible packaging applications.
Nylons are very resistant to chemicals. For this reason, the multi-storey HDPE bottles preferred for the packaging of pesticides and similar substances use nylon as the solvent barrier and the innermost layer that comes into contact with the product. Polyamide or nylon has very low oxygen permeability and can also be used in multilayer bottles where the oxygen barrier is required.