What are the forms of plastic packaging that can be seen in life?

As long as we touch food, we can see the figure of plastic packaging. The reason why plastic packaging can become an indispensable part of the food system is that the plastic material is small in density, light in weight, transparent or opaque, and easy to form and process as long as the mold is replaced, different varieties of containers are easy to form mass production. But it also has a lot of shortcomings such as: plastic deformation at high temperature surface hardness is low and easy to wear; It will degrade and become brittle under light oxygen and hot oxygen. Poor electrical conductivity, easy to produce electrostatic accumulation and even pollution links. But in spite of this, it has brought great convenience to our lives. Alan. According to Aaron Brody, a food packaging consultant and associate professor of food science at the University of Georgia, the plastic revolution in food packaging began in the 1960s. Plastic is chosen because it is lighter than glass, stronger than paper, and cheaper. But as Brody points out, "there is no universal plastic." Many of the packaging bags we come into contact with are made from a combination of different types of food packaging plastics. We can see a variety of forms of plastic packaging in our lives, and there are several common ones: potato chip packaging bags its main component is a kind of plastic called "oriented polypropylene". "It's a good moisture barrier," Brody explains. In the packaging of potato chips, moisture is crucial, "because the chips absorb moisture and start to spoil." Nobody is going to like wet crisps." For further reinforcement, many potato chip bags also have a thin layer of aluminum added to the inner layer. The trade name and nutritional information are printed on the outer layer, while a layer of polyethylene is sandwiched between the inner and outer layers. Brody also said that most companies inject nitrogen into the bags before they are sealed. "This will prevent the chips from crushing." While oxygen oxidizes the fat in the chips, creating the flavor, nitrogen doesn't cause any of the chemical reactions that ruin the flavor. Food companies often spend a lot of time designing packaging with the goal of best preserving every product they sell. That's what the army does, too. In previous reports, the Army has used a packaging to extend the shelf life of sandwiches to two years. The salad bag is the same as the potato chip bag, that is, the ready-to-eat vegetable salad bag is also made of polypropylene, and is also injected with a bag of nitrogen gas. Unlike potato chips, salad leaves need to breathe a little oxygen, which is why they have tiny holes in their bags. "Small holes allow oxygen to come in and carbon dioxide to come out," Brody said. He added that the bags often have a thin anti-fog layer on the inside, "so that condensation does not occur and consumers can see the beautiful green leaves." When making many plastic packages, manufacturers worry not only about how to keep the air out, but also how to keep the water vapor inside. This is important in the packaging of ice cream, for example, Brody says. A tub of ice cream must be easy to open and close, but it must also have a tight seal that keeps the moisture inside and keeps the texture smooth. Stored in the refrigerator, sublimation sometimes occurs, which is the phenomenon that water goes directly from a solid to a gas. "Once sublimated water is lost, it cannot be restored, whereas ice cream can become sandy and clumpy if it loses water." "Brody said. Certainly, as food expert Herbert. According to Stone, even after all the research and development, most plastic packaging is still not able to preserve food in extreme environments. Stone is a food industry consultant and past president of the Institute of Food Technicians. "When food companies use plastic containers, they have to make sure they don't change the taste of the food," Stone said. He added that plastic is not an inert material and can react with other chemicals. And unlike many glass or metal products, it also allows air to pass through. Have you ever left a plastic water bottle in a hot car for too long? Then it probably tastes funny. But the reason is not what you might think: it's not because the chemicals in the plastic leach into the water. Stone explained that small amounts of air can penetrate plastic, and when the temperature increases, the movement of air will also be accelerated. Heat also speeds up chemical reactions. When the chemicals in the bottle react with each other, or with substances in the external environment, the water in the bottle will taste strange. Leave a bottle of soda in a hot car, and the carbonation will quickly escape from the bottle. "All that's left is the sodas." "Plastic is convenient, but it's not a panacea," Mr. Stone said. In addition to being technically limited, all the plastic packaging we use today generates a lot of waste. In 2012 alone, the United States generated 14 million tons of plastic waste that used to be bags and containers. Plastic doesn't biodegrade easily, so it sometimes ends up in the ocean, which not only harms Marine life, but can even contaminate seafood. While many types of plastic can already be recycled, the shiny packaging that contains multiple layers of plastic is difficult to recycle because different types of plastic are disposed of separately at recycling stations.