In our daily life, we are exposed to plastic bags every day, which is an essential part of our life. However, few friends know the material of plastic bags.1. PlasticThere are also plastics used in food packaging in my country15species or6species, such as polyethylene, polypropylene, polystyrene,the pet,PA,PVDC,EVA,PVA,EVOH,pvc, ion-bonding resins, etc., among whichPVA,EVOH,PVDC,the pet,PAGood oxygen resistance,PVDC,PP,PEGood moisture resistance,P.S.Good radiation resistance such as aromatic nylon,PE,EVAWait, low temperature resistantPOETER,PAetc.; high temperature and low temperature resistant ionomer resins,PA,the petetc., with good oil resistance and mechanical properties, such asthe pet,PAWait. Different types of plastics have different monomers, different degrees of polymerization, different types and amounts of additives, and different properties, even different brands of the same plastic have different properties. Therefore, it is necessary to choose the appropriate plastic or the combination of plastic and other materials according to the needs. Improper selection will lead to a decline in food quality and even loss of food value.2. Composite materialsPlastic packaging bag composite material is a flexible packaging material with a wide variety of applications. Currently, the plastics used for food packaging are30There are hundreds of types of multilayer composites containing plastics. Composite materials are generally2-6layer, but special needs can be achieved10layer above. The scientific and rational use of plastic, paper or paper towels, aluminum foil and other substrates can almost meet the packaging requirements of various foods. For example, the shelf life of Tetra Pak milk made of multi-layer materials such as plastic cardboard, aluminum plastic and plastic can reach half a year to one year. Some high barrier meat cans have a shelf life of up to3Years, the shelf life of compound packaging cakes in some developed countries can reach1more than a year. One year later, the nutrition, color, aroma, taste, shape and microbial content of the cake still meet the requirements. In the design of composite packaging, special attention should be paid to the selection of each layer of base material, the collocation must be scientific and reasonable, and the comprehensive performance of each layer combination must meet the overall requirements of food packaging.