PVC ( Polyvinyl chloride )

 

Polyvinyl chloride
Density 1380 kg/m3
Young's modulus (E) 2900-3400 MPa
Tensile strength(σt) 50-80 MPa
Elongation @ break 20-40%
Notch test 2-5 kJ/m2
Glass temperature 87 °C
Melting point 212 °C
Vicat B1 85 °C
Heat Transfer Coefficient (λ) 0.16 W/m.K
Linear Expansion Coefficient (α) 8 10-5 /K
Specific heat (c) 0.9 kJ/(kg·K)
Water absorption (ASTM) 0.04-0.4
 
Polyvinyl chloridePolyvinyl chloride, (IUPAC über Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. 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 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. 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. The material is often used for pipelines in the water and sewer industries because of its inexpensive nature and flexibility.

Preparation
Polyvinyl chloride is produced by polymerization of the monomer vinyl chloride, as shown.

History
Polyvinyl chloride was accidentally discovered on at least two different 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 (Polyvinyl Chloride) 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.

Applications

Electric wires
PVC is commonly used as the insulation on electric wires; the plastic used for this purpose needs to be plasticized. In a fire, PVC-coated wires can form HCl fumes; the chlorine serves to scavenge free radicals and is the source of the material's fire retardance. However, these (intentional) fumes can also pose a health hazard in their own right. Frequently in applications where smoke is a major hazard (notably in tunnels) PVC-free LSOH (low-smoke, zero-halogen) cable insulation is used.

Pipes
Polyvinylchloride is also widely used for producing pipes. About 90% of all PVC pipes are used for drainage and for protecting/containing cables in buildings

Unplasticized polyvinyl chloride (uPVC)
 
Modern "Tudorbethan" house with uPVC gutters and downpipes, fascia, decorative imitation "half-timbering", windows and doors.uPVC is often used in the building industry as a low maintenance material, particularly in the UK, and in the USA where it is known as vinyl.The material comes in a range of colours and finishes, including a photo-effect wood finish, and is used as a substitute for painted wood, most obviously for window frames and sills when installing double glazing in new buildings or to replace older single glazed windows. It has many other uses including fascia, and siding or weatherboarding. The same material has almost entirely replaced the use of cast iron for plumbing and drainage, being used for waste pipes, drainpipes, gutters and downpipes.

Due to environmental concerns use of PVC is discouraged by some local and authoritiesand in countries such as Germany and The Netherlands.

Health and safety
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Phthalate plasticizers
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. Vinyl IV bags used in neo-natal intensive care units have also been shown to leach DEHP (Bis(2-ethylhexyl) phthalate), a phthalate additive. In January 2006, the European Union to placed a ban on six types of phthalate softeners in toys (See directive 2005/84/EC). In 2003, the US Consumer Product Safety Commission (CPSC) denied a petition for a similar ban in the United States however, 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 this information is preliminary and further study is needed.

According to MIT professor Dr. Makhlook Singh, the properties of PVC may be useful for biological applications as well. He noted the fungi Indiamycetes seems to bond well with the surface of PVC and begins to break down the carbon chains of the PVC. The fungus soon dies, but it leaves behind a toxin resin coating that has been shown to reduce Concentrations of many types of bacteria. He is excited about new pharachological use of this resin. However, further tests will be needed to determine the usefulness of this toxic resin.

According to some medical studies, the plasticizers added to PVC may cause chronic conditions such as scleroderma, cholangiocarcinoma, angiosarcoma, brain cancer, and acroosteolysis. PVC has been used in many products for many years and still there is not proof of significant harmful effects from exposure. There have been studies, some cited in this article, that indicate links with certain medical problems and exposure to PVC products.

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.Alternative plasticisers are being developed but in many cases these alternatives remain significantly more expensive and their technical performance varies. It is also worth noting that some, though not all, of the alternatives pose significant health risks.

In November 2005, one of the largest hospital networks in the U.S., Catholic Healthcare West, signed a contract with B.Braun for vinyl-free intravenous bags and tubing.[8] According to the Center for Health, Environment & Justice[3] in Falls Church, VA, which helps to coordinate a "precautionary" "PVC Campaign", a slew of major corporations including Microsoft, Wal-Mart, and Kaiser Permanente announced efforts to eliminate PVC from products and packaging in 2005.


Vinyl chloride monomer
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 UK 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.

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."

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.

Dioxins
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. The European Industry, however, asserts that it has improved production processes to minimize dioxin emissions. 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. The US EPA estimate of dioxin releases from the PVC industry (based on industry estimates) more than doubled between 1995 and 2000.

The largest well-quantified source of dioxin in the US EPA inventory of dioxin sources is barrel burning of household waste. Studies of household waste burning indicate consistent increases in dioxin generation with increasing PVC concentrations.According to the EPA dioxin inventory, landfill fires are likely to represent an even larger source of dioxin to the environment. A survey of international studies consistently identifies high dioxin concentrations in areas affected by open waste burning and a study that looked at the homologue pattern found the sample with the highest dioxin concentration was “typical for the pyrolysis of PVC”. Other EU studies indicate that PVC likely “accounts for the overwhelming majority of chlorine that is available for dioxin formation during landfill fires.”

The next largest sources of dioxin in the EPA inventory are medical and municipal waste incinerators. Studies have shown a clear correlation between dioxin formation and chloride content and indicate that PVC is a significant contributor to the formation of both dioxin and PCB in incinerators.

PVC is not typically recycled due to the prohibitive cost of regrinding and recompounding the resin compared to the cost of virgin (unrecycled) resin.

The thermal depolymerization process can safely and efficiently convert PVC into fuel and minerals, according to the company that developed it. It is not yet in widespread use.