Polyvinyl chloride (pol-ee-VYE-nul KLOR-ide) is also known as PVC, vinyl, chlorethylene homopolymer, and chlorethene homopolymer. It is the third most commonly produced plastic in the United States, exceeded only by polyethylene and polypropylene. It is offered commercially in a variety of formulations, usually as a white powder or colorless granules. The compound is resistant to moisture, weathering, most acids, fats and oils, many organic solvents, and attack by fungi. It is easily colored and manufactured in a variety of forms, including sheets, films, fibers, and foam.
Carbon, hydrogen, chlorine
Decomposes at 148°C (298°F)
Insoluble in water; soluble in tetrahydrofuran, dimethyllformamide, dimethylsulfoxide
Polyvinyl chloride was first discovered accidentally in 1835 by the French physicist and chemist Henry Victor Regnault (1810–1878). Regnault found that a container of gaseous vinyl chloride (CH2CH=Cl) exposed to the sunlight gradually changed to a white powder. Regnault knew almost nothing about the composition of the powder or how it was formed. Polyvinyl chloride remained a subject of little or no interest to chemists for almost a century. German and Russian chemists made some efforts to find useful applications for the compound in the early twentieth century, without much success. The first patent for the production of the compound was awarded to the German chemist Friedrich Heinrich August Klatte (dates not available) in 1913, but Klatte never marketed the product for commercial use.
Then, in 1926, Waldo Lonsbury Semon (1898–1999), a chemist at B. F. Goodrich, rediscovered polyvinyl chloride, once again by accident. Semon had been assigned the task at Goodrich of finding a substitute for natural rubber as a lining for metal tanks and for finding a material that would bond the rubber substitute to the metal tank. One of the materials he studied was polyvinyl chloride. In his work, Semon did not so much rediscover polyvinyl chloride as to find new ways of working with the material. For example, he found that he could dissolve the compound in various organic solvents, converting them so that they could be molded, extruded, and formed. He also discovered that he could control the properties of the material by altering the amount of solvent used to dissolve powdered polyvinyl chloride.
Goodrich adapted Semon's discovery for two specific applications: shoe heels and the coating on chemical racks. Those applications were not profitable enough for Goodrich to continue making polyvinyl chloride. But Semon continued to look for new ways of adapting the compound for additional applications. He was eventually successful and by 1931 the company had begun to turn out a full line of polyvinyl chloride products in most of the forms currently available.
- The recycling symbol for polyvinyl chloride is the number 3 inside a triangle made of three arrows.
- The environmental group Greenpeace has called for a global ban on the production of polyvinyl chloride because the toxic substance dioxin is released (albeit, in very small amounts) as a byproduct of the compound's production.
HOW IT IS MADE
Polyvinyl chloride is made by polymerizing vinyl chloride (CH2=CHCl). Polymerization occurs when the double bond in vinyl chloride breaks, allowing one molecule of vinyl chloride to combine with a second molecule of vinyl chloride: CH2=CHCl + CH2=CHCl → CH3CHClCH=CHCl. The product of that reaction also contains a double bond, allowing the reaction to be repeated: CH3CHClCH=CHCl + CH2=CHCl → CH3CHClCH2CHClCH=CHCl. Once again, the final product contains a double bond, and the reaction can be repeated again and again and again. The reaction is made possible by using some agent to cause double bonds to break. In the original experiments carried out by Regnault, Klatte, and others, that agent was sunlight. Chemists have long since learned, however, that a variety of chemicals known as peroxide initiators are more effective at breaking double bonds. Peroxide initiators are compounds with an oxygen-oxygen bond (-O-O-). One of the most widely used initiators is benzoyl peroxide (C6H5CO-O-O-C6H5CO).
COMMON USES AND POTENTIAL HAZARDS
An estimated 7 billion kilograms (15.7 billion pounds) of polyvinyl chloride were produced in the United States in 2006. It is available in more than 50 trade names, including Airex, Armodour, Astralon, Benvic, Bonloid, Chemosol, Chlorostop, Dacovin, Dorlyl, Flocor, Lucoflex, Norvinyl, Opalon, Polivinit, Polytherm, Sicron, Takilon, Vinikulon, Viniplast, and Wilt Pruf. About three-quarters of that amount was made in a rigid format that is hard and inflexible. The remaining one-quarter was made in a flexible form, produced by adding materials to polyvinyl chloride that make it soft and pliable. About 75 percent of all rigid polyvinyl chloride (half of all the compound made in the United States) goes to the construction industry. It has replaced older building materials such as clay, concrete, and wood because it is inexpensive, lightweight, resistant to damage by the sun, and easy to assemble. The compound is used to make vinyl siding, windows, plumbing pipes, flooring, electric cables, roofing materials, and insulation for cables and wires.
Flexible polyvinyl chloride is used to make fibers and films for applications such as clothing, upholstery, plastic bottles, medical equipment, lightweight toys, shower curtains, and packaging films. Some of the medical equipment produced from polyvinyl chloride include bags to hold blood and other fluids, artificial heart valves, and tubes used in kidney dialysis. Medical products made from polyvinyl chloride are strong enough to be air-dropped to troops in combat zones. Automobile manufacturers use polyvinyl chloride in body side moldings, interior upholstery, engine wiring, floor mats, adhesives, dashboards, arm rests, and coatings under the vehicle.
The commercial and household products containing polyvinyl chloride are generally regarded as posing no threat to human health. However, a number of questions have been raised about possible health hazards and risks to the environment as a result of the process by which polyvinyl chloride is made, some of its applications, and its eventually disposal. For example, polyvinyl chloride is made from vinyl chloride, which itself is toxic and a carcinogen. People who work with vinyl chloride in production facilities are at risk for developing a form of liver cancer that may be related to exposure to vinyl chloride. Vinyl chloride, in turn, is made from chloride, a very toxic gas that poses health risks to people who work with it.
Some environmental health experts point out that products made of polyvinyl chloride may give off toxic or carcinogenic gases for short periods of time after they have been put into use. For example, shower curtains and automobile upholstery containing polyvinyl chlorides may release hazardous chemicals into the air for a few months after they are first installed.
Some concern has also been expressed about additives used with polyvinyl chloride. For example, some of the substances used to soften the compound belong to a family known as the phthalates, which are known carcinogens with toxic effects. Some health experts point out that infants may ingest small amounts of phthalates from PVC toys they chew on.
Finally, the disposal and destruction of compounds containing polyvinyl chloride may create environmental problems. Burning such products, for example, releases hydrogen chloride gas, a suffocating and toxic gas, into the atmosphere. Enough concern about the health and environmental hazards has arisen that some governmental bodies in Europe have placed limitations on the uses to which PVC products can be put.
FOR FURTHER INFORMATION
"Healthy Building Network." http://www.healthybuilding.net/ (accessed on October 29, 2005).
Meikle, Jeffrey L. American Plastic: A Cultural History. Piscataway, N.J.: Rutgers University Press, 1997.
Thornton, Joe. "Environmental Impacts of Polyvinyl Chloride (PVC) Building Materials." A briefing paper for the U.S. Green Building Council, n.d. Available online at http://www.usgbc.org/Docs/LEED_tsac/PVC/CMPBS%20Original%20Submittal.pdf (accessed on October 29, 2005).
"Vinyl—The Material." The Vinyl Institute. http://www.vinylinfo.org/materialvinyl/history.html (accessed on October 29, 2005).
Polyvinyl chloride, also known as PVC, is a plastic produced by the polymerization of vinyl chloride . It is used with plasticizers to make packaging films, boots, garden hose, etc. Without plasticizers, PVC is used to make pipe, siding, shingles, window frames, toys, and other items. An attractive aspect of PVC for industry is its ability to withstand weathering and its resistance to chemicals and solvents. However, this attractive aspect is the major environmental concern for PVC and many other plastics . The great bulk of such plastic (about 98%) is neither reused nor recycled but occupies ever dwindling landfill space.