亚中文字幕国产综合_自拍av影片色欲色_亚洲日韩av免费_欧美人成网址18禁止久久影院_一级高清视频www_6080yy无码一区二区播放_黄色淫片免费看_亚洲午夜一区在线观看_美国特级oo毛片免费香蕉_日日碰狠狠躁

    In today's life. The rhythm is very fast. Many foods are packaged in plastic bags and eaten directly and conveniently. Modern food packaging materials mainly include plastic, paper, composite materials (plastic/plastic, plastic/paper, plastic/aluminium, foil/paper/plastic and other types of multi-layer composite materials), glass bottles, metal cans and so on. Today's packaging bags are mainly made of composite materials and plastic packaging.
    1. Composites
    Composite material is a kind of soft packaging material with the most kinds and the most widely used. At present, there are more than 30 kinds of plastics used in food packaging, and there are more than 100 kinds of multi-layer composite materials containing plastics. Composite materials generally use 2-6 layers, but special needs can reach 10 or more layers. The combination of plastics, paper or paper machine, aluminum foil and other substrates can meet the packaging requirements of almost all kinds of food. For example, the shelf life of milk packaged in Lele can be as long as six months to one year, which is made of     plastic/cardboard/aluminium plastic/plastic and other multi-layer materials. The shelf life of some canned meat with high barrier can be as long as 3 years, and that of some composite packaging cakes in developed countries can be more than one year. After one year, the nutrition, color, fragrance, taste, shape and microbial content of cakes still meet the requirements. In the design of composite packaging, special attention should be paid to the selection of substrates for each layer, the collocation must be scientific and reasonable, and the comprehensive performance of each layer combination must meet the comprehensive requirements of food packaging.
    2. Plastics
    There are fifteen or six kinds of plastics for food packaging in China, such as PE, PP, PS, PET, PA, PVDC, EVA, PVA, EVOH, PVC, ionic bond resin, etc. Among them, there are PVA, EVOH, PVDC, PET, PA, etc. with high oxygen resistance, PVDC, PP, PE with high moisture resistance, PS aromatic nylon with radiation resistance, PE, EVA, POET and PA with low temperature resistance, and ionic bond resins, PA, PET with good oil resistance and mechanical properties, such as high temperature sterilization and low temperature resistance, such as PET, PA, etc. Various plastics have different molecular structures, degree of polymerization, types and quantities of additives, and different properties, even though different brands of the same plastics have different properties. Therefore, it is necessary to select suitable plastics or combinations of plastics and other materials according to the requirements, and improper selection may lead to deterioration of food quality or even loss of edible value.
    The above content is about the use of more composite materials and plastic bags in packaging materials, hoping to help you, plastic bags for our life has provided great convenience, in addition to food, such as clothing is used more, as well as express packaging bags.