The oxygen resistance of EVOH is obviously higher than that of any other materials, about - 10000 times of that of polyethylene, but it will change with the change of relative humidity. EVOH also has excellent barrier performance to carbon dioxide, nitrogen, helium and other gases. EVOH not only has excellent barrier performance to aroma components, but also has little adsorption capacity on its surface. The performance of PA is the same as EVOH. With the increase of humidity, the oxygen resistance of PA decreases rapidly. At 100% humidity, the oxygen resistance of PA is 1 / 4 of that at 30%. In addition, the size of PA changes when it comes to water, so we seldom see high humidity products directly packaged with PA. PVDC material, due to its symmetrical molecular structure and the existence of hydrophobic chlorine, can ensure that the oxygen permeability does not change with the change of humidity. The results show that the oxygen resistance of EVOH (38%) is better than that of PVDC when the humidity is 0% ~ 70%, and the oxygen resistance performance of PVDC is better than that of EVOH when the humidity is more than 80%. EVOH is a new type of barrier material. Its gas resistance is 100 times higher than that of PA (polyamide), 10000 times higher than that of PE and PP, and more than 10 times higher than PVDC (polyvinylidene chloride) which is commonly used at present. Meanwhile, EVOH has the highest thermal stability among high performance barrier resins.
The most significant characteristic of EVOH resin is its gas barrier effect. It is used in packaging structures to improve flavor and quality retention by preventing oxygen penetration. In the use of inflatable packaging technology, EVOH resin effectively retains the carbon dioxide or nitrogen used to protect the product. Because of the hydroxyl groups in the molecular structure of EVOH resin, EVOH resin has hydrophilicity and hygroscopicity. When the moisture is adsorbed, the barrier performance of the gas will be affected. In the field of packaging, EVOH is made into composite film intermediate barrier layer, which is used in all hard and soft packaging; in the food industry, it is used for aseptic packaging, hot cans and cooking bags, and for packaging dairy products, meat, juice cans and condiments; in non food, it is used for packaging solvents, chemicals, air conditioning structural parts, gasoline barrel lining, electronic components, etc. In terms of food packaging, EVOH plastic containers can completely replace glass and metal containers. Many domestic aquatic companies use nine layer coextrusion film vacuum packaging for seafood export. At the same time, EVOH stretching orientation is also studied in foreign countries. The gas barrier performance of the new EVOH film is three times higher than that of the existing high-performance non stretched EVOH film.
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