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2018

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What is foamed PVC

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Foamed PVC is the common name of polyvinyl chloride (polyvinyl chloridem, PVC). Since polyvinyl chloride itself is relatively hard, it needs to add more foaming agent, so it is sometimes called foamed PVC.

1. Physical and chemical properties: Polyvinyl chloride is polymerized from vinyl chloride as a monomer.

Molecular weight: about 50,000~120,000

According to the amount of plasticizer added to PVC, it can be divided into hard, semi-rigid and soft PVC. The plasticizer added to hard PVC is generally <10%, semi-rigid is 10-30%, and soft is 30-50%. Its physical and mechanical properties also vary with its components. In general, PVC has the characteristics of good chemical resistance, high mechanical strength, good insulation and low price. PVC semi-rigid sheets can be processed into plastic boxes by blister; soft polyvinyl chloride can be used as gaskets for beverage caps and four-spin bottle caps (commonly known as drop plastic); rigid polyvinyl chloride can be processed into plastic tubes, plates, etc. wait.

2. Main hygienic problems: polyvinyl chloride itself is non-toxic, but its monomers and degradation products are highly toxic, and the content of plasticizer in polyvinyl chloride is relatively high.

(1) Toxicity of vinyl chloride monomer and degradation products: PVC resin and molded products often contain a certain amount of vinyl chloride monomer, which can migrate into food when in contact with food. After vinyl chloride is absorbed through the gastrointestinal tract, part of it is excreted through the respiratory tract, and the other part is decomposed into chlorohydrin and monochloroacetic acid. It can also combine with deoxyribonucleic acid (DNA) in vivo. Mainly toxic to the nervous system, bones and liver. The research results show that vinyl chloride monomer and its decomposition products are carcinogenic. There are epidemiological investigation reports of human angiosarcoma. Therefore, all countries have regulations on the residual amount of vinyl chloride monomer in polyvinyl chloride resin. For example, Japan, the United States, the United Kingdom, France, the Netherlands, Italy, Switzerland and other countries stipulate that it should be less than 1mg/kg; France, Italy, and Switzerland also stipulate that food The migration amount should not be greater than 0.05mg/kg. my country's GB4803-94 "Hygienic Standards for Polyvinyl Chloride Resins for Food Containers and Packaging Materials" and GB9681-88 "Hygienic Standards for Polyvinyl Chloride Molded Products for Food Packaging" stipulate that polyvinyl chloride resins for food packaging and vinyl chloride single Body content should be controlled below 5mg/kg and 1mg/1 respectively.

(2) Toxicity of halogenated hydrocarbons: According to the preparation method of vinyl chloride monomer, polyvinyl chloride is divided into two types: acetylene method polyvinyl chloride and ethylene method polyvinyl chloride. Due to different synthesis processes, the halogenated hydrocarbons contained in polyvinyl chloride are also different. Acetylene-based polyvinyl chloride contains 1,1-dichloroethane, while ethylene-based polyvinyl chloride contains 1,2-dichloroethane, and the latter is 10 times more toxic than the former. Therefore, GB4803-94 "Hygienic Standards for Vinyl Chloride Resin Used in Food Containers and Packaging Materials" stipulates that in acetylene method polyvinyl chloride resin, the residual amount of 1,1-dichloroethane should be less than 150mg/kg; The residual amount of 1,2-dichloroethane in the resin should be less than 2mg/kg.

(3) Migration of plasticizers: A large amount of plasticizers are used in PVC molded products, especially semi-rigid and soft PVC, some of which are more toxic (see Table 5.1). ??????? In addition to plasticizers, additives such as stabilizers and ultraviolet absorbers are also added when producing PVC molded products, and these additives will also migrate to food. Therefore, it is also necessary to pay great attention to the toxicity of additives. It should meet the requirements of GB9685-94 "Hygienic Standards for the Use of Auxiliaries for Food Containers and Packaging Materials".