The hottest Hu Yadong comments on food preservativ

2022-08-19
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Hu Yadong commented on food preservative film materials PE and PVC

the famous chemist Hu Yadong recently described in detail the merits and demerits of the two main materials PE and PVC currently used in food preservative films:

according to the current information, the food preservative films produced in China are mainly made of PE materials, but some supermarket fresh products such as vegetables, fruits and cooked food packaging are largely made of PVC preservative films, More than 80% of these products come from Japan and South Korea. In addition, according to experts, PVC food preservative film is relatively harmful to human body. Harmful substances in this kind of preservative film are easy to be separated out. After entering the human body with food, it has carcinogenic effect on human body, especially interfering with human endocrine, causing women's breast cancer, neonatal congenital defects, male reproductive disorders and even mental diseases. It is precisely because of the serious harm that Europe banned the use of PVC as food packaging materials as early as a few years ago. Japan also eliminated PVC food in 2000 and accelerated the transformation of enterprise packaging. According to the World Packaging Organization Council, the United States, Japan, Singapore, South Korea and European countries have now completely banned the use of PVC packaging materials

however, this kind of food preservative film came into China in 1995. From the beginning, the annual consumption is only a few tons, and the current annual consumption is more than 15000 tons on the electric box of the universal experimental machine base

Hu Yadong said that PE (polyethylene) is a very safe chemical material, which is absolutely no problem for food preservation. In contrast, PVC, that is, polyvinyl chloride, is a polymer of chemical substances called vinyl chloride. Vinyl chloride itself is harmful to human body. Although its polymer polyvinyl chloride is harmless in principle, the polymerization of any chemical substances is not complete. Therefore, a certain amount of vinyl chloride has not been completely polymerized, but it cannot be separated from it. These unpolymerized vinyl chloride is the "culprit" of carcinogenesis of PVC materials

pe and PVC are both hard plastics. In addition to making fresh-keeping film, they have many similar uses. Safety and long service life are the strengths of PE materials. From the analysis of the extraction methods of these two materials, Hu Yadong believes that the production cost of PE should be lower than that of PVC, because it is extracted directly from oil, while PVC has an additional processing process in production. There are also production methods of extracting PVC from alcohol or acetylene, but its cost will be higher

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pvc itself is also relatively hard, but when making products made of PVC, plasticizers are usually added to improve the softness, and products that are thick but also very soft can be made. The harm of PVC fresh-keeping film to human health also comes from the harmful chemical components of plasticizers

but at present, PVC is more widely used than PE, because it has the advantage that plasticizers can be easily added to make it adapt to the requirements of different thickness and softness. Therefore, most of the thicker plastic films used in outer packaging are made by using PV pendulum impact testing machine and the method C that shows the difference between the potential energy before and after impact on the dial. Generally, when using PE materials, plasticizers are not added; If thicker materials are needed, PE is not soft enough, so the fresh-keeping film made of PE is generally very thin. The most familiar thing about the use of PVC material is that it is widely used to make cables. The sleeves we often contact and used to bury wires during decoration are also made of PVC material with a small amount of plasticizer. In this application, PVC material is basically harmless to human body

in the 1960s, Hu Yadong specialized in the research of PVC materials. At that time, the full mixing of PVC and plasticizer was still a scientific problem in China. Hu Yadong said that PVC powder is hard and spherical under the microscope, and it is not easy to mix with plasticizers. The subject of their cooperation with Beijing No. 2 chemical plant is to make PVC powder softer, porous and easy to mix with plasticizers. Hu Yadong said that at that time, phosphophthalic anhydride and phosphophthalic anhydride ester were widely used as plasticizers, mainly for industrial materials. At present, ethylhexylamine (DEHA) is widely used as plasticizer in food fresh-keeping film, which is easier to mix with PVC and can account for a large proportion. The harm of PVC fresh-keeping film to human health also comes from the harmful chemical components of plasticizer. However, compared with phosphophthalic anhydride and phosphophthalic anhydride used in industry before, this plasticizer has a longer service life and relatively less harm to human body because of its stable mixing and difficult decomposition

although PVC is more widely used, PE is better in terms of total use. One of the most famous cables in the world - the submarine cable from Britain to the United States is made of PE. Because the component containing "chlorine" in PVC material is easy to decompose, the cable made of PVC material is easy to age and become brittle, and its service life is relatively low, which cannot meet the service life of 50 ~ 100 years required at that time. The chemical composition of PE is relatively stable and its service life is long. The cable has no much requirements for flexibility. Therefore, PE material is used when making cables. Hu Yadong said that this is probably the most famous "case" of PE materials in use

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