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Polyvinyl chloride

Polyvinyl chloride (PVC) is a widely-used plastic. In terms of revenue generated, it is one of the most valuable products of the chemical industry. Globally, over 50% 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 have been raised about the environmental and human health costs of PVC.

Polyvinyl chloride is produced from its monomer, vinyl chloride (chemical formula CH2=CHCl). PVC is a hard plastic that is made softer and more flexible by the addition of plasticizers, the most widely used being phthalates.

There are many uses for PVC including vinyl siding, window profiles, gramophone records (hence the ones made of this material are sometimes called vinyl records) pipe/plumbing/conduit fixtures, bean bags; and, in its soft form, for clothing, upholstery (car seats), flooring, roofing membranes, electrical cables, etc.

 

Atomic structure

 
H H H H H H \ / | | | | C == C --> ... -- C -- C -- C -- C -- ... / \ | | | 
| Cl H Cl H Cl H Vinyl chloride monomer Polyvinyl chloride polymer 

History

Polyvinyl chloride was accidentally discovered on at least two occasions in the 19th century, first in 1838 by Henri Victor Regnault and in 1872 by Eugen Baumann. On both occasions, the polymer appeared as a white solid inside flasks of vinyl chloride that had been left exposed to sunlight. In the early 20th century, the Russian chemist Ivan Ostromislensky and Fritz Klatte of the German chemical company Griesheim-Elektron both attempted to use PVC in commercial products, but difficulties in processing the rigid, sometimes brittle polymer blocked their efforts.

In 1926, Waldo Semon of B.F. Goodrich developed a method to plasticize PVC by blending it with various additives. The result was a more flexible and more easily processed material that soon achieved widespread commercial use.

Health and safety

Most vinyl products are believed to be generally harmless when used properly. However, some of the additives and softeners can leach out of certain vinyl products. Even though 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. Vinyl IV bags used in neo-natal intensive care units have also been shown to leach DEHP (di-2-ethyl hexyl phthalate), a phthalate additive. In December 1999 the European Commission placed a temporary ban on the use of phthalate additives in PVC toys for children under the age of three. This was a precautionary measure taken because no validated test method existed at the time to determine the true level of migration of phthalates from individual toys. In 2003 the US Consumer Product Safety Commission (CPSC) denied a petition for a similar ban in the United States but in the USA most companies have voluntarily stopped manufacturing PVC toys for this age group or have eliminated the phthalates. In a draft guidance paper published in September 2002, the US FDA recognizes that many medical devices with PVC containing DEHP are not used in ways that result in significant human exposure to the chemical. However, FDA is suggesting that manufacturers consider eliminating the use of DEHP in certain devices that can result in high aggregate exposures for sensitive patient populations such as e.g. neonates. However, alternative softeners have not been properly tested to determine whether they are safe. Other vinyl products like brand new car interiors, shower curtains, and flooring, to name a few, initially release chemical gases into the air. Some studies indicate that this outgassing of additives may contribute to health complications, but the information on this is preliminary and needs further study.

According to some medical studies, the plasticizers added to PVC may cause chronic conditions such as Raynaud's syndrome, scleroderma, cholangiocarcinoma, angiosarcoma, brain cancer and acroosteolysis.

In the late 1960's, Dr. John Creech, and Dr. Maurice Johnson, were the first to clearly link and recognize the carcinogenicity of vinyl chloride monomer to humans; workers in the polyvinyl chloride polymerization section of a B.F. Goodrich plant near Louisville, Kentucky, were diagnosed with liver angiosarcoma, a rare disease. Since that time, studies of PVC workers in Australia, Italy, Germany, and the U.K. have all associated certain types of occupational cancers with exposure to vinyl chloride. The link between angiosarcoma of the liver and long-term exposure to vinyl chloride is the only one which has been confirmed by the International Agency for Research on Cancer.

The environmentalist group Greenpeace has advocated the global phase-out of PVC because they claim dioxin is produced as a byproduct of vinyl chloride manufacture.

In 2004, a joint Swedish-Danish research team found a very strong link between allergies in children and the phthalates DEHP and BBzP, commonly used in PVC. On the other hand, a study by the US Institute of Medicine "Cleaning the Air" concluded that there is "insufficient evidence of a link" between phthalates in vinyl flooring and childhood asthma.

The European Industry, however, has improved production processes to minimize dioxin emissions. Alternative plasticisers are being developed but these alternatives remain significantly more expensive and their technical performance is sometimes not as good as for phthalates.

Resin identification code

The symbol for polyvinyl chloride developed by the Society of the Plastics Industry so that items can be labelled for easy recycling is:

The Unicode character for PVC is U+2675 (HTML ♵).

See also

External links


 

 

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