Polyvinyl chloride

From Freepedia

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.

Contents

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 1835 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 plasticizers 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 neonates. However, alternative softeners have not been properly tested to determine whether they are more or less safe. Other vinyl products, including car interiors, shower curtains, flooring, etc., 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. It is worth noting that PVC products have been widely used for many years without significant, demonstrable health effects.

In the late 1960s, Dr. John Creech and Dr. Maurice Johnson were the first to clearly link and recognize the carcinogenicity of vinyl chloride monomer to humans when 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. All the cases of angiosarcoma developed from exposure to vinyl chloride monomer, were in workers who were exposed to very high VCM levels, routinely, for many years.

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 and from incineration of waste PVC in domestic garbage.

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. It is also unclear whether these alternatives really represent a reduction in health risk.

According to the EPA, "vinyl chloride emissions from polyvinyl chloride (PVC), ethylene dichloride (EDC), and vinyl chloride monomer (VCM) plants cause or contribute to air pollution that may reasonably be anticipated to result in an increase in mortality or an increase in serious irreversible, or incapacitating reversible illness. Vinyl chloride is a known human carcinogen which causes a rare cancer of the liver." [FEDERAL REGISTER Vol. 63, No. 83 (April 30, 1998), pgs. 23785- 23786.]

A front-page series in the HOUSTON CHRONICLE claimed the vinyl industry has manipulated vinyl chloride studies to avoid liability for worker exposure and to hide extensive and severe chemical spills into local communities. [See Jim Morris, "In Strictest Confidence . The chemical industry's secrets," HOUSTON CHRONICLE. Part One: "Toxic Secrecy," June 28, 1998, pgs. 1A, 24A-27A; Part Two: "High-Level Crime," June 29, 1998, pgs. 1,A, 8A, 9A; and Part Three: "Bane on the Bayou," July 26, 1998, pgs. 1A, 16A.]

Vinyl chloride production is also inherently a source of dioxins, a highly toxic substance that can cause cancer and other illnesses in humans even at very low exposure levels. Dioxins are a global health threat because they persist in the environment and can travel long distances. At very low levels, near those to which the general population is exposed, dioxins have been linked to immune system suppression, reproductive disorders, a variety of cancers, and endometriosis. According to a 1994 report by the British firm, ICI Chemicals & Polymers Ltd., "It has been known since the publication of a paper in 1989 that these oxychlorination reactions [used to make vinyl chloride and some chlorinated solvents] generate polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs). The reactions include all of the ingredients and conditions necessary to form PCDD/PCDFs.... It is difficult to see how any of these conditions could be modified so as to prevent PCDD/PCDF formation without seriously impairing the reaction for which the process is designed." In other words, dioxins are an unavoidable consequence of making PVC. Dioxins created by vinyl chloride production are released by on-site incinerators, flares, boilers, wastewater treatment systems and even in trace quantities in vinyl resins. [See Pat Costner and others, "PVC: A Primary Contributor to the U.S. Dioxin Burden; Comments submitted to the U.S. EPA Dioxin Reassessment," (Washington, D.C. Greenpeace U.S.A., February 1995).]

Dioxins are formed in virtually all combustion where the the necessary atoms are available in the fuel. Studies have shown that municipal waste incineration is a much bigger source of dioxin production than the PVC industry. Additional studies have shown that PVC in the municipal waste does not have a significant impact on the amount of dioxin generated.

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: Image:Recycle-resin-logos-lr 03.png

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

See also

External links

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