Polyvinyl Chloride

Polyvinyl chloride is one of the most important thermoplastic materials. Polyvinyl chloride is finding wide application both in industrial and agriculture productions and in daily life for its benefits and advantages.

Polyvinyl Chloride is finding wide application both in industrial and agriculture productions and in daily life, owing to its rich resources, low costs, good mechanical properties and corrosion resistance.

Generally speaking, polyvinyl chloride is obtained by the polymerization of monomer vinyl chloride, or in more detail, it is prepared by heating water emulsion of vinyl chloride in the presence of a small amount of benzoyl peroxide as catalyst in closed vessels under pressure. Thus, monomer vinyl chloride is the foundation of polyvinyl chloride.

There are a lot of ways to obtain monomer vinyl chloride. Mainly it is obtained by reacting acetylene with hydrochloric acid gas, or by reacting ethylene obtained by cracking petroleum with chlorine to form ethane bichloride, then cracking it to give vinyl chloride.

Polyvinyl chloride is obtained as a white fluffy powder which, when hot molded alone, can be converted into a hard, horny mass. When it is hot masticated with 50 to 100 percent of its weight of plasticizer, a profound change in properties is brought about. This plasticized PVC is rubbery and is extremely tough and flexible. PVC decomposes fairly readily when overheated, therefore temperatures must be carefully controlled during processing.

Polyvinyl chloride has a succession of large negative chlorine atoms on alternate carbon atoms, which stiffen the main chain by both steric hindrance and electronic repulsion and also provide intermolecular attraction between adjacent chains. The configuration is also fairly regular, producing 5% to 10% crystallinity. Altogether these forces produce fairly rigid, strong products that have good chemical resistance and soften gradually at higher temperatures. The high crystalline melting point, however, makes for difficult process ability, and the aliphatic chlorine atoms permit dehydrochlorination, which produces poor thermal stability. Polyvinyl chloride is more important in plasticized form.

With variety of plasticizer and stabilizer, PVC can be made in soft, rigid or transparent form, which can be molded by injection or extrusion into many items such as raincoats, curtains, toys, and radio components.