Polyvinyl chloride is a polymer material that uses one chlorine atom to replace one hydrogen atom in polyethylene. A thermoplastic resin polymerized from vinyl chloride under the action of an initiator is a homopolymer of vinyl chloride. Polyvinyl chloride is the world's largest plastic product with low price and wide application. Polyvinyl chloride resin is white or light yellow powder.
PVC resin was produced in the 1930s, and it was the largest output of plastics in the world for a long period of time. With the development of polyolefin plastics, it is now the second largest. Has excellent chemical stability and flame retardant properties.
Classification
It is the largest and most important petrochemical raw material for chemical building materials. Based on polyvinyl chloride resin and adding one or more auxiliary components with certain functions, it is called polyvinyl chloride plastic, which is divided into rigid polyvinyl chloride plastic, soft polyvinyl chloride plastic, polyvinyl chloride plastic Vinyl paste, etc.
About the Production Process
PVC is synthesized from vinyl chloride by free radical polymerization. From suspension polymerization, emulsion polymerization and bulk polymerization, suspension polymerization is the main method, accounting for about 80% of the total output of PVC. In the industry, the PVC production process is generally distinguished according to the obtaining method of ethylene monomer, which can be divided into calcium carbide method and ethylene method. According to different production methods, PVC pure powder is divided into general-purpose PVC resin, high polymerization degree PVC resin, and cross-linked PVC resin.
General-purpose PVC resin is formed by the polymerization of vinyl chloride monomer under the action of an initiator. High degree of polymerization PVC resin refers to the resin obtained by adding a chain extender to the vinyl chloride monomer polymerization system.
Cross-linked PVC resin is a resin that is polymerized by adding a cross-linking agent containing diene and polyene to the vinyl chloride monomer polymerization system.
Is PVC resin safe?
Polyvinyl chloride resin is a kind of high molecular polymer, which is generally less toxic. Thermal decomposition occurs only at high temperatures to generate atmospheric hydrogen and olefin gases that are harmful to the human body. PVC itself is not toxic. However, the main auxiliary materials such as plasticizers and antioxidants added are toxic. The plasticizers in daily PVC plastics mainly use dibutyl terephthalate, dioctyl phthalate, etc. These chemicals All are toxic, and lead stearate, an antioxidant for polyvinyl chloride, is also toxic. Lead will be precipitated when PVC products containing lead salt antioxidants come into contact with ethanol, acetaldehyde and other solvents. Polyvinyl chloride containing lead salt is used as food packaging and when it encounters fried dough sticks, fried cakes, fried fish, cooked meat products, cakes and snacks, lead molecules will diffuse into the oil, so polyvinyl chloride plastic bags cannot be used. Contained food, especially not oily food.