Polyvinyl Chloride (Pvc)
Polyvinyl chloride (PVC) is a macromolecule that results from the free-radical polymerization of vinyl chloride. First discovered in the early 1870s, PVC has become widely distributed second only to polyethylene in annual production volume. It has many desirable characteristics finding use as a construction material, packaging resin, and textiles coating.
The discovery of PVC was first described in 1872. It was found when a container of vinyl chloride was exposed to sunlight and a white solid was produced. This material was of interest because it was resistant to degradation by potassium hydroxide or water. From 1912 to 1926 German scientists attempted to process PVC into more usable products. In 1926, it was found that when PVC was boiled in tricresyl phosphate it became elastic. This new reaction made PVC an important material and produced the first thermoplastic elastomer.
Depending on the grade required, PVC can be produced by a variety of techniques including suspension, emulsion, solution, microsuspension, and mass polymerization. Suspension polymerization is the most often used procedure. It involves the suspension of monomer particles in water. Stabilizers prevent coalescence while the polymerization reaction proceeds. After 80-90% of the reaction is complete, excess monomer and water is removed and the polymer is dried with hot air.
The bulk properties of PVC depend on the production method. It can be produced as droplets suspended in water, a thin membrane, a powder or crystals. To improve the workability of PVC resin various ingredients are added to the resin including stabilizers, impact modifiers, lubricants, plasticizers, biocides and flame retardants.
PVC is employed in a variety of applications. The principle market for PVC is as a base material for pipes and fittings. It is also used as a weathering material because it is less damaged by exposure to sunlight. PVC makes an excellent resin for clear bottles that hold consumer products. In addition, PVC is used as an insulating material for cables and wires.
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