What kind of material is PVC?

Polyvinyl chloride, referred to as PVC, is a polymer made of vinyl chloride as a monomer through free radical polymerization. Because the electron-withdrawing substituent of the chlorine atom on vinyl chloride is p-π conjugated, has an electron-donating effect, and is not easily attacked by carbanions, so free radical polymerization can only be used. The current PVC polymerization process includes suspension polymerization (above 80%), bulk polymerization (about 7%), emulsion polymerization, microsuspension polymerization, etc.

PVC has good impact resistance, mechanical strength, dielectric properties and other aspects, so it has a wide range of applications and was once the world's largest output of general-purpose plastics. Common products include coatings, pipes, plastic steel, carpets, packaging materials, etc. There are two common preparation methods for PVC monomer vinyl chloride (VCM). One is the addition of acetylene and HCl to produce vinyl chloride. The raw material calcium carbide in this method comes from coal, and it requires a lot of electricity, which consumes a lot of money and costs a lot. high. (Some domestic factories still use this method.) Another method is the ethylene oxychlorination method, in which ethylene and chlorine generate 1,2-dichloroethylene and then crack to generate vinyl chloride. Because the main raw materials come from petroleum and alkali industry, low energy consumption and low cost, it is now gradually replacing the calcium carbide method.

Vinyl chloride is a carcinogen, and polyvinyl chloride contains residual vinyl chloride monomers. Therefore, polyvinyl chloride has certain carcinogenicity and was listed as a third-class carcinogen in 2017. (Common Class 3 carcinogens include gasoline, diesel, naphthalene sanitary balls, etc.) The current PVC production process has been able to ensure that the residual monomer content in PVC is extremely low, and qualified PVC can be safely used in food packaging and other aspects.