PVC (Molecule of the Month for April 2007)
Polyvinyl chloride, Polychloroethene
Polyvinyl chloride (PVC) is a widely used thermoplastic polymer. Most of PVC manufactured is used in construction. As a building material, PVC is cheap and easy to assemble. In recent years, PVC has been replacing traditional building materials such as wood, concrete and clay in many areas. Despite appearing to be an ideal building material, concerns were raised about the costs of PVC to the natural environment and human health. There are many uses for PVC. As a hard plastic, it is used as vinyl siding, magnetic stripe cards, window profiles, gramophone records (which is the source of the name for vinyl records), pipe, plumbing and conduit fixtures. The material is often used in Plastic Pressure Pipe Systems for pipelines in the water and sewer industries because of its inexpensive nature and flexibility. It can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates. In this form, it is used in clothing and upholstery, and to make flexible hoses and tubing, flooring, to roofing membranes, and electrical cable insulation.
Polyvinyl chloride is produced by polymerization of the monomer vinyl chloride, as shown. Since a significant proportion of its mass is chlorine, creating a given mass of PVC requires less petroleum than many other polymers.
Many vinyl products contain additional chemicals to change the chemical consistency of the product. Some of these additional chemicals called additives can leach out of vinyl products. Plasticizers which must be added to make PVC flexible have been an additive of particular concern. Because soft PVC toys have been made for babies for years, there are concerns that these additives leach out of soft toys into the mouths of the children chewing on them. In January 2006, the European Union placed a ban on six types of phthalate softeners used in toys. A new process of PVC Recycling is being developed in Europe and Japan called Vinyloop®. This process consists of recovering PVC plastic from composite materials through dissolution and precipitation.
Update by Karl Harrison
(Molecule of the Month for April 2007 )