Plastic wrap can be divided into three categories. The first is polyethylene, or PE for short, which is mainly used for food packaging. The fruit and vegetable films we usually buy, including semi-finished products bought in the supermarket, are made of this material; The second is PVC, which can also be used for food packaging, but it has a certain impact on human safety; The third is polyvinylidene chloride, PVDC for short, which is mainly used for the packaging of some cooked food, ham and other products. Among the three kinds of fresh-keeping films, PE and PVDC are safe to human body and safe to use. However, PVC fresh-keeping film is not suitable for heating and can not be used for cooked food. Therefore, PE fresh-keeping film should be selected when purchasing fresh-keeping film.
From a physical point of view, the fresh-keeping film has moderate oxygen and moisture permeability, which can adjust the oxygen and water content around the fresh-keeping products, block dust, and prolong the shelf life of food. Therefore, it is necessary to choose different preservative films for different foods.

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