Detection and production :


About 80% of production involves suspension polymerization. Emulsion polymerization accounts for about 12% and bulk polymerization accounts for 8%. Suspension polymerizations afford particles with average diameters of 100 – 180 μm, whereas emulsion polymerization gives too much small particles of average size around 0.2 μm. VCM and water are presented into the reactor and a polymerization initiator, along with other additives. The reaction vessel is pressure tight to contain the VCM. The contents of the reaction vessel are continually mixed to keep the suspension and ensure a uniform particle size of the PVC resin. The reaction is exothermic, and thus needs cooling. As the volume is decrease during the reaction (PVC is denser than VCM), water is continually added to the mixture to maintain the suspension.

The polymerization of VCM is begun by compounds called initiators that are mixed into the droplets. These compounds break down to start the radical chain reaction. Typical initiators contain dioctanoyl peroxide and dicetyl peroxydicarbonate, both of which have brittle O-O bonds. Some initiators start the reaction rapidly but decay quickly and other initiators have the opposite result. A mixture of two different initiators is often used to give a uniform rate of polymerization. After the polymer has grown by about 10x, the short polymer precipitates inside the droplet of VCM, and polymerization continues with the precipitated, solvent-swollen particles. The weight average molecular weights of commercial polymers has a range which start from 100,000 to 200,000 and the number average molecular weights range begin from 45,000 to 64,000.

Once the reaction has run its course, the resulting PVC slurry is degassed and stripped to eliminate extra VCM, which is recycled. The polymer is then passed through a centrifuge to remove water. The slurry is further dried in a hot air bed, and the resulting powder sieved before storage or pelletization. Normally, the resulting PVC has a VCM content of less than 1 part per million. Other production processes, for example micro-suspension polymerization and emulsion polymerization, making PVC with smaller particle sizes (10 μm vs. 120–150 μm for suspension PVC) with slightly dissimilar properties and with different sets of applications.