Foamed PVC is the common name for polyvinyl chloride (PVC). Since polyvinyl chloride itself is hard, more foaming agents need to be added, so it is sometimes called foamed PVC.

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

Molecular weight: about 50,000 to 120,000

According to the amount of plasticizer added to polyvinyl chloride, it can be divided into hard, semi-hard and soft polyvinyl chloride. The plasticizer added to hard polyvinyl chloride is generally less than 10%, 10 to 30% for semi-hard, and 30 to 50% for soft. Its physical and mechanical properties also vary with its components. In general, polyvinyl chloride 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 through blister forming; soft PVC can be used as gaskets for beverage caps and four-screw bottle caps (commonly known as drip molding); rigid PVC can be processed into plastic pipes, plates, etc. ?

2. Main health issues: PVC itself is non-toxic, but its monomers and degradation products are highly toxic, and the content of plasticizers in PVC is relatively high. ?

(1) Toxicity of vinyl chloride monomer and degradation products: PVC resins 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 by the gastrointestinal tract, part of it is excreted through the respiratory tract, and the other part is decomposed into chloroethanol and monochloroacetic acid. It can also bind to deoxyribonucleic acid (DNA) in the body. It mainly produces toxic effects on the nervous system, bones and liver. Research results show that vinyl chloride monomer and its decomposition products are carcinogenic. There are epidemiological survey reports on human angiosarcoma. Therefore, all countries have set 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 1 mg/kg; France, Italy and Switzerland also stipulate that the migration amount in food should not be greater than 0.05 mg/kg. China's GB4803-94 "Sanitary Standard for Polyvinyl Chloride Resins for Food Containers and Packaging Materials" and GB9681-88 "Sanitary Standard for Polyvinyl Chloride Molded Products for Food Packaging" stipulate that the content of vinyl chloride monomer in polyvinyl chloride resins and molded products for food packaging should be controlled below 5 mg/kg and 1 mg/1 respectively.

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

(3) Migration of plasticizers: A large amount of plasticizers are used in polyvinyl chloride molded products, especially semi-rigid and soft polyvinyl chloride, some of which are highly toxic. In addition to plasticizers, additives such as stabilizers and ultraviolet absorbers must be added when producing polyvinyl chloride molded products. These additives will also migrate into food. Therefore, great attention must also be paid to the toxicity of the added additives. It should comply with the provisions of GB9685-94 "Sanitary Standard for the Use of Additives for Food Containers and Packaging Materials".

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