“High barrier” is undoubtedly a very ideal property, which is one of the required properties of many polymer packaging materials.
In technical terms, high barrier means very low permeability to low molecular weight chemicals such as gases and organic compounds.
High barrier packaging materials can effectively maintain the original performance of the product, extend the life of the product.
Common High Barrier Material Types
At present, the common barrier material types in polymer materials are as follows:
1. Polyvinylidene chloride (PVDC)
PVDC has excellent barrier to oxygen and water vapor.
PVDC high crystallinity, high density, and the presence of hydrophobic group makes its oxygen transmission rate and the gas permeable rate is extremely low, thus make PVDC has excellent gas barrier property, compared with other materials can be better to extend the shelf life of packaged goods, together with its good printing adaptability, easy to heat sealing, and thus is widely used in food and pharmaceutical packaging.
EVOH is a copolymer of ethylene and vinyl alcohol. This is because the molecular chain of EVOH contains hydroxyl groups, and the hydroxyl groups on the molecular chain are easy to form hydrogen bonds, so that the intermolecular forces are strengthened, the molecular chain accumulation is more compact, and the crystallinity of EVOH is higher, thus having excellent barrier performance.
However, EVOH structure contains a large number of hydroxyl groups with hydrophilicity. It makes EVOH easy to absorb moisture, thus greatly reducing the barrier performance. In addition, high intermolecular cohesion and high crystallinity lead to poor thermal sealing performance.
3. Polyamide (PA)
Generally speaking, nylon has good air resistance, but poor resistance to water vapor, strong water absorption, and with the increase in water absorption and swelling, so that the air resistance, moisture resistance performance drops sharply, its strength and the stability of the package size will also be affected.
In addition, the mechanical properties of nylon, tough wear-resisting, cold and heat resistance, good chemical stability, easy processing, printing, but poor heat sealing.
4. Polyester (PET, PEN)
The most common and widely used barrier material in polyester is PET. PET has excellent barrier performance due to its symmetrical chemical structure, good planar molecular chain, compact molecular chain and easy crystallization orientation.
In recent years, PEN has been applied and developed rapidly, which has good hydrolysis resistance, chemical resistance and uv resistance. The structure of PEN is similar to that of PET, except that the main chain of PET contains benzene ring, while the main chain of PEN contains naphthalene ring.
Due to the larger conjugate effect of naphthalene and benzene ring, higher molecular chain rigidity and more planar structure, PEN has better comprehensive performance than PET.
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