What is polyvinyl chloride

What is polyvinyl chloride(PVC)

Polyvinyl chloride (PVC) is the third most produced synthetic polymer plastic in the world (after polyethylene and polypropylene), producing approximately 40 million tons of PVC per year. PVC is a polymer of vinyl chloride monomer (VCM) polymerized in peroxide, azo compound and other initiators or under the action of light and heat according to free radical polymerization reaction mechanism. Vinyl chloride homopolymer and vinyl chloride copolymer are called vinyl chloride resin.

PVC was once the world's largest production of general purpose plastic, the application is very wide. PVC has two types: hard (sometimes abbreviated as RPVC) and soft. Rigid polyvinyl chloride is used for construction pipes, doors and Windows. It is also used to make plastic bottles, packaging, bank cards or membership cards. Adding plasticizers can make PVC softer and more flexible. It can be used for plumbing, cable insulation, flooring, signage, phonograph records, inflatable products and rubber substitutes.

Constituent structure     

Polyvinyl chloride is a polymer material that uses a chlorine atom to replace a hydrogen atom in polyethylene. It is an amorphous polymer containing a small amount of crystalline structure. This material has the following structure: -(CH2-CHCl)n-. PVC is a linear polymer in which VCM monomers are mostly associated with a head-tail structure. The carbon atoms are arranged in a zigzag pattern, and all atoms are linked by sigma bonds. All carbon atoms are sp3 hybrid.

There is a short intertonal structured structure on the PVC molecular chain. The degree of syntactic regularity increases with the decrease of polymerization temperature. Polyvinyl chloride macromolecular structure has head structure, branch chain, double bond, allyl chloride, tertiary chloride and other unstable structures, resulting in poor heat deformation and aging resistance. After pretending to cross-link, this kind of shortcoming can be eliminated.

Main classification    

According to the different application scope, PVC can be divided into: universal PVC resin, high polymerization degree PVC resin, cross-linked PVC resin. General purpose PVC resin is formed by polymerization of vinyl chloride monomer under the action of initiator; High polymerization degree PVC resin refers to the resin which is polymerized by adding chain growth agent in the polymerization system of vinyl chloride monomer; Crosslinked PVC resin is a resin which is polymerized by adding crosslinker containing diene and polyene into vinyl chloride monomer polymerization system.

According to the method of obtaining vinyl chloride monomer, it can be divided into calcium carbide method, ethylene method and imported (EDC, VCM) monomer method (customary ethylene method and imported monomer method are called ethylene method).

According to the polymerization method, PVC can be divided into four categories: suspension polyvinyl chloride, emulsion polyvinyl chloride, bulk polyvinyl chloride and solution polyvinyl chloride. Suspension polyvinyl chloride is the largest variety of production, accounting for about 80% of the total production of PVC. Suspension polyvinyl chloride is divided into six models according to absolute viscosity: XS-1, XS-2... XS-6; XJ-1, XJ-2... , XJ-6. The meaning of each letter in the model: X-suspension method; S-loose type; J-compact type.

According to the plasticizer content, PVC plastic is often divided into: no plasticizer PVC, plasticizer content is 0; Rigid PVC, plasticizer content is less than 10%; Semi-rigid PVC, plasticizer content is 10-30%; Soft PVC, plasticizer content is 30-70%; Polyvinyl chloride paste plastic, plasticizer content of more than 80%.