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Why does the fresh-keeping bag leak oil?
The main purpose of fresh-keeping bag is to isolate bacteria and viruses and ensure that food will not rot. Therefore, according to the design, the fresh-keeping bag should be able to penetrate small and medium molecules, otherwise it would not be a fresh-keeping bag. Completely isolated from gas and water, food will also be stuffy and form another kind of corruption under low oxygen conditions. Ideally, the fresh-keeping bag is not isolated from oxygen, so that anaerobic bacteria can not survive. At the same time, it is isolated from bacteria, and ordinary aerobic bacteria floating in the air can not enter food.
After careful study, it can be found that the instructions of fresh-keeping bags generally introduce indicators such as oxygen permeability and air permeability. Why do oxygen, carbon dioxide and water molecules penetrate plastic films? Because the polymer compounds that make up the plastic film, such as polyethylene, are composed of many molecular chains, and there are large or small gaps between them for molecules to pass through. The molecular weight of carbon dioxide and oxygen is tens, and the molecular weight of oil is hundreds. To ensure that most holes can pass through oxygen and water molecules, it is inevitable that some large holes can slowly squeeze oil molecules through. Therefore, the fresh-keeping bag is oily.
However, the fresh-keeping bag can still isolate bacteria. Because of the small virus and the total molecular weight of 100000 to million, the oily fresh-keeping bag still has the function of fresh-keeping. Now there are even fresh-keeping bags specially marked with micropores, which have better air permeability and can still isolate bacteria. It can be seen that the principle of fresh-keeping bags is that the molecular weight of bacteria virus is much greater than that of oxygen and water, and plastic "sieves" are used to reduce the probability of bacteria invading food. As for the formation of this screen hole, it does not affect the work of the fresh-keeping bag. The molecular weight of oil is close to oxygen and far away from bacteria, so it can seep through the fresh-keeping bag.
The polymer compounds that make up the plastic film have voids that can pass through oxygen and water molecules, and oil molecules will also pass through such holes. This is the reason why the fresh-keeping bag leaks oil. Its purpose is to isolate bacteria and viruses, and oil molecules are not within the range of interception. So we can only accept this fact helplessly. Perhaps with the development of science and technology, the gap between polymers can be controlled more accurately, and then the problem of oil leakage in fresh-keeping bags can be solved.
