| Elongation at break | 20–40% |
|---|---|
| Notch test | 2–5 kJ/m2 |
| Glass temperature | 82 °C[1] |
| Melting point | 100–260 °C[1] |
| Effective heat of combustion | 17.95 MJ/kg |
| Specific heat (c) | 0.9 kJ/(kg·K) |
| Water absorption (ASTM) | 0.04–0.4 |
Polyvinyl chloride, commonly abbreviated PVC, is the third most widely produced plastic, after polyethylene and polypropylene.[2] PVC is widely used in construction because it is durable, cheap, and easily worked. PVC production is expected to exceed 40 million tonnes by 2016.[3] [4]
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, electrical cable insulation, inflatable products and many applications in which it replaces rubber.[5]
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PVC was accidentally discovered at least twice in the 19th century, first in 1835 by Henri Victor Regnault and then 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. Waldo Semon and the B.F. Goodrich Company developed a method in 1926 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.
Polyvinyl chloride is produced by polymerization of the monomer vinyl chloride (VCM), as shown.[6]
About 80% of production involves suspension polymerization. Emulsion polymerization accounts for about 12 % and bulk polymerization is 8 %. In suspension polymerization. Suspension polymerizations affords particles with average diameters of 100 – 180 mm, whereas emulsion polymerization gives much smaller particles of average size around 0.2 mm. VCM and water are introduced into the reactor and a polymerization initiator, along with other additives. The reaction vessel is pressure tight to contain the VCM. The contents of the reaction vessel are continually mixed to maintain the suspension and ensure a uniform particle size of the PVC resin. The reaction is exothermic, and thus requires cooling. As the volumes also contract during the reaction (PVC is denser than VCM), water is continually added to the mixture to maintain the suspension[7]
The reaction is initiated by compounds called initiators. These compounds break down into radicals that then start the radical chain reaction. Typical initators include dioctanoyl peroxide and dicetyl peroxydicarbonate, both of which have fragile O-O bonds. Some iniators start the reaction rapidly but decay quickly and other initiators have the opposite properties, thus a combination of two different intiators is often used. After the polymer chain has grown to about 10x, the short polymer precipitates inside the droplet of VCM, and polymerization continues with the precipitated, solvent-swollen particles. The weight averaged molecular weights of commercial polymers range from 100,000 to 200,000 and the number average molecular weights range from 45,000 to 64,000.
Once the reaction has run its course, the resulting PVC slurry is degassed and stripped to remove excess VCM, which is recycled. The polymer is then passed though a centrifuge to remove water. The slurry is further dried in a hot air bed, and the resulting powder sieved before storage or pelletization. Normally, the resulting PVC has a VCM content of less than 1 part per million. Other production processes, such as micro-suspension polymerization and emulsion polymerization, produce PVC with smaller particle sizes (10 μm vs. 120–150 μm for suspension PVC) with slightly different properties and with somewhat different sets of applications.
The polymers is linear. The monomers are mainly arranged head-to-tail, meaning that there are chlorides on alternating carbon centres.PVC has mainly an atactic stereochemistry, which means that the relative stereochemistry of the chloride centres are random. Some degree of syndiotacticity of the chain gives a few percent crystallinity that is influential on the properties of the material. About 57% of the mass of PVC is chlorine. The presence of chloride groups gives the polymer very different properties from the structurally related material polyethylene.[8]
The product of the polymerization process is unmodified PVC. Before PVC can be made into finished products, it always requires conversion into a compound by the incorporation of additives such as heat stabilizers, UV stabilizers, lubricants, plasticizers, processing aids, impact modifiers, thermal modifiers, fillers, flame retardants, biocides, blowing agents and smoke suppressors, and, optionally pigments.[9]
Most vinyl products contain plasticizers which dramatically improve their performance characteristic. The most common plasticizers are derivatives of phthalic acid. The materials are selected on their compatibility with the polymer, their low volatility, their low toxicity, and their cost. These materials are usually oily colourless substances that mix well with the PVC particles. 90% of the plasticizer market, estimated to be millions of tons per year worldwide, is dedicated to PVC.[9]
Phthalates can be divided into two groups: high and low molecular weight with high molecular phthalates now representing over 80 percent of European market for plasticisers. Low molecular weight phthalates include those with 3-6 carbon atoms in their chemical backbone; the most common types being Di-2-ethylhexyl phthalate (DEHP), Di-butyl phthalate (DBP), Di- isobutyl phthalate (DIBP) and Butyl benzyl phthalate (BBP). They represent about 15% of the European market. High molecular weight phthalates include those with 7-13 Carbon atoms in their chemical backbone, which gives them increased permanency and durability. The most common types of high phthalates include di-isononyl phthalate (DINP) and di-isodecyl phthalate (DIDP). The European market has been shifting in the last decade from low to high phthalates, which today represent over 80% of all the phthalates currently being produced in Europe.
One of the most crucial additives are heat stabilizers. These agents minimize loss of HCl, a degradation process that starts above 70 °C. Once dehydrochlorination starts, it is autocatalytic. Many diverse agents have been used including, traditionally, derivatives of heavy metals (lead, cadmium). Increasingly, metallic soaps (metal "salts" of fatty acids) are favored, species such as calcium stearate.[7]
PVC is a thermoplastic polymer. Its properties for PVC are usually categorized based on rigid and flexible PVCs.
| Property | Rigid PVC | Flexible PVC |
|---|---|---|
| Density [g/cm3][10] | 1.3–1.45 | 1.1–1.35 |
| Thermal conductivity [W/(m·K)][11] | 0.14–0.28 | 0.14–0.17 |
| Yield strength [MPa][10] | 31–60 | 10–25 |
| Young's modulus [psi] | 490,000[12] | |
| Flexural strength (yield) [psi] | 10,500[12] | |
| Compression strength [psi] | 9500[12] | |
| Coefficient of thermal expansion (linear) [mm/(mm °C)] | 5×10−5[12] | |
| Vicat B [°C][11] | 65–100 | Not recommended |
| Resistivity [Ω m][13][14] | 1016 | 1012–1015 |
| Surface resistivity [Ω][13][14] | 1013–1014 | 1011–1012 |
PVC's relatively low cost, biological and chemical resistance and workability have resulted in it being used for a wide variety of applications. It is used for sewerage pipes and other pipe applications where cost or vulnerability to corrosion limit the use of metal. With the addition of impact modifiers and stabilizers, it has become a popular material for window and door frames. By adding plasticizers, it can become flexible enough to be used in cabling applications as a wire insulator. It has been used in many other applications.
Roughly half of the world's polyvinyl chloride resin manufactured annually is used for producing pipes for municipal and industrial applications.[15] In the water distribution market it accounts for 66% of the market in the US, and in sanitary sewer pipe applications, it accounts for 75%.[16] Its light weight, high strength, and low reactivity make it particularly well-suited to this purpose. In addition, PVC pipes can be fused together using various solvent cements, or heat-fused (butt-fusion process, similar to joining HDPE pipe), creating permanent joints that are virtually impervious to leakage.
In February, 2007 the California Building Standards Code was updated to approve the use of chlorinated polyvinyl chloride (CPVC) pipe for use in residential water supply piping systems. CPVC has been a nationally accepted material in the US since 1982; California, however, has permitted only limited use since 2001. The Department of Housing and Community Development prepared and certified an environmental impact statement resulting in a recommendation that the Commission adopt and approve the use of CPVC. The Commission's vote was unanimous and CPVC has been placed in the 2007 California Plumbing Code.
In the United States and Canada, PVC pipes account for the largest majority of pipe materials used in buried municipal applications for drinking water distribution and wastewater mains.[17] Buried PVC pipes in both water and sanitary sewer applications that are 4 inches (100 mm) in diameter and larger are typically joined by means of a gasket-sealed joint. The most common type of gasket utilized in North America is a metal reinforced elastomer, commonly referred to as a Reiber sealing system.[18]
PVC is commonly used as the insulation on electrical cables; PVC 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. While HCl fumes can also pose a health hazard in their own right, HCl dissolves in moisture and breaks down onto surfaces, particularly in areas where the air is cool enough to breathe, and is not available for inhalation.[19] Frequently in applications where smoke is a major hazard (notably in tunnels and communal areas) PVC-free cable insulation is preferred, such as low smoke zero halogen (LSZH) insulation.
uPVC or rigid PVC is extensively used in the building industry as a low-maintenance material, particularly in Ireland, the United Kingdom, and in the United States. In the USA it is known as vinyl, or vinyl siding.[20][21] The material comes in a range of colors and finishes, including a photo-effect wood finish, and is used as a substitute for painted wood, mostly 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 downspouts.[22] uPVC does not contain phthalates or BPA. Most dental retainers and mouthguards are made from uPVC. uPVC does not have the same concerns as flexible PVC. Phthalates are only added to flexible PVC. uPVC is also known as rigid PVC, uPVC is known as having strong resistance against chemicals, sunlight, and oxidation from water.[23]
Polyvinyl chloride is formed in flat sheets in a variety of thicknesses and colors. As flat sheets, PVC is often expanded to create voids in the interior of the material, providing additional thickness without additional weight and minimal extra cost (see Closed-cell PVC foamboard). Sheets are cut using saw and rotary cutting equipment. Plasticized PVC is also used to produce thin, colored, or clear, adhesive-backed films referred to simply as vinyl. These films are typically cut on a computer-controlled plotter or printed in a wide-format printer. These sheets and films are used to produce a wide variety of commercial signage products and markings on vehicles, e.g. car body stripes.
PVC has become widely used in clothing, to either create a leather-like material or at times simply for the effect of PVC. PVC clothing is common in Goth, Punk and alternative fashions. PVC is cheaper than rubber, leather, and latex which it is therefore used to simulate.
PVC fabric has a sheen to it and is waterproof so is used in coats, skiing equipment, shoes, jackets, aprons, and bags.
PVC has been used for a host of consumer products of relatively minor volume compared to the industrial and commercial applications described above. Another of its earliest mass-market consumer applications was to make vinyl records. More recent examples include greenhouses, home playgrounds, foam and other toys, custom truck toppers (tarpaulins), ceiling tiles and other kinds of interior and exterior cladding (see uPC).
PVC can be usefully modified by chlorination, which increases its chlorine content a few percent. The new material is even more rugged and more rigid, but it is expensive and it is found only in niche applications, such as certain hot water heaters and certain specialized clothing. CPVC, as it is called, is produced from aqueous suspensions of PVC particles swollen with chlorinated solvents. Treatment of this mixture with chlorine followed by exposure to UV-light initiates the free-radical chlorination.[7]
PVC is a useful material because of its inertness and this inertness is the basis of its low toxicity: "There is little evidence that PVC powder itself causes any significant medical problems."[7] The main health and safety issues with PVC are associated with "VCM", its carcinogenic precursor, the products of its incineration (dioxins under some circumstances), and the additives mixed with PVC, which include heavy metals and potential endocrine disruptors. "Fear of litigation ... have all but eliminated fundamental research into VCM polymerization."[7]
Probably the greatest impact of PVC on health and safety have been highly positive. It has revolutionized the safe handling of sewage and being affordable, its use is widespread outside of developed countries.[7]
It has been claimed that some plasticizers leach out of PVT products. However plasticizers do not readily migrate and leach into the environment from flexible vinyl articles because they are physically and tightly bound into the plastic as a result of the heating process used to make PVC particles. Vinyl products are pervasive including toys,[24] car interiors, shower curtains, and flooring initially release chemical gases into the air. Some studies indicate that this outgassing of additives may contribute to health complications, and have resulted in a call for banning the use of DEHP on shower curtains, among other uses.[25] The Japanese car companies Toyota, Nissan, and Honda have eliminated PVC in their car interiors starting in 2007.
In 2004 a joint Swedish-Danish research team found a statistical association between allergies in children and indoor air levels of DEHP and BBzP (butyl benzyl phthalate), which is used in vinyl flooring.[26] In December 2006, the European Chemicals Bureau of the European Commission released a final draft risk assessment of BBzP which found "no concern" for consumer exposure including exposure to children.[27]
Risk assessments have led to the classification of low molecular weight and labelling as Category 1B Reproductive agents. Three of these phthalates, DBP, BBP and DEHP were included on annex XIV of the REACH regulation in February 2011 and will be phased out by the EU by February 2015 unless an application for authorisation is made before July 2013 and an authorisation granted. DIBP is still on the REACH Candidate List for Authorisation. The European Union has confirmed that DEHP poses no general risk to human health. The summary of a comprehensive European risk assessment, involving nearly 15 years of extensive scientific evaluation by EU regulators, was published in the EU Official Journal on February 7, 2008 [28] The assessment demonstrated that DEHP poses no risk to the general population and that no further measures need to be taken to manage the substance in any of its key end-use applications. This confirms an earlier opinion of member state experts and an opinion from the EU Scientific Committee for Toxicity, Ecotoxicity and the Environment (CSTEE) adopted in 2004. The only areas of possible risk identified in the assessment relate to
In 2008 the European Union's Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) reviewed the safety of DEHP in medical devices. The SCENIHR report states that certain medical procedures used in high risk patients result in a significant exposure to DEHP and concludes there is still a reason for having some concerns about the exposure of prematurely born male babies to medical devices containing DEHP.[29] The Committee said there are some alternative plasticizers available for which there is sufficient toxicological data to indicate a lower hazard compared to DEHP but added that the functionality of these plasticizers should be assessed before they can be used as an alternative for DEHP in PVC medical devices. Risk assessment results have shown positive results regarding the safe use of High Molecular Weight Phthalates. They have all been registered for REACH and do not require any classification for health and environmental effects, nor are they on the Candidate List for Authorisation. High phthalates are not CMR (carcinogenic, mutagenic or toxic for reproduction), neither are they considered endocrine disruptors.
In the EU Risk Assessment the European Commission has confirmed that Di-isononyl phthalate (DINP) and Di-isodecyl phthalate (DIDP) pose no risk to either human health or the environment from any current use. The European Commission’s findings (published in the EU Official Journal on April 13, 2006)[30] confirm the outcome of a risk assessment involving more than 10 years of extensive scientific evaluation by EU regulators. Following the recent adoption of EU legislation with the regard to the marketing and use of DINP in toys and childcare articles, the risk assessment conclusions clearly state that there is no need for any further measures to regulate the use of DINP. In Europe and in some other parts of the world, the use of DINP in toys and childcare items has been restricted as a precautionary measure. In Europe, for example, DINP can no longer be used in toys and childcare items that can be put in the mouth even though the EU scientific risk assessment concluded that its use in toys does not pose a risk to human health or the environment. The rigorous EU risk assessments, which include a high degree of conservatism and built-in safety factors, have been carried out under the strict supervision of the European Commission and provide a clear scientific evaluation on which to judge whether or not a particular substance can be safely used.
The FDA Paper titled "Safety Assessment of Di(2-ethylhexyl)phthalate (DEHP)Released from PVC Medical Devices" states that [3.2.1.3] Critically ill or injured patients may be at increased risk of developing adverse health effects from DEHP, not only by virtue of increased exposure, relative to the general population, but also because of the physiological and pharmacodynamic changes that occur in these patients, compared to healthy individuals.[31]
In the early 1970s, the carcinogenicity of vinyl chloride (usually called vinyl chloride mononomer or VCM) was linked to cancers in workers in the polyvinyl chloride industry. Specifically workers in polymerization section of a B.F. Goodrich plant near Louisville, Kentucky (US) were diagnosed with liver angiosarcoma also known as hemangiosarcoma, a rare disease.[32] 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. Since that time, it has become accepted that VCM is a carcinogen.[7] Technology for removal of VCM from products have become stringent commensurate with the associated regulations.
PVC produces HCl upon combustion almost quantitatively related to its chlorine content. Extensive studies in Europe indicate that the chlorine found in emitted dioxins is not derived from HCl in the flue gases. Instead, most dioxins arise in the condensed solid phase by the reaction of inorganic chlorides with graphitic structures in char-containing ash particles. Copper acts as a catalyst for these reactions.[33]
Studies of household waste burning indicate consistent increases in dioxin generation with increasing PVC concentrations.[34] 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."[34]
The next largest sources of dioxin in the EPA inventory are medical and municipal waste incinerators.[35] Various studies have been conducted that reach contradictory results. For instance a study of commercial-scale incinerators showed no relationship between the PVC content of the waste and dioxin emissions.[36][37] Other 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.[38][39][40]
In February 2007, the Technical and Scientific Advisory Committee of the US Green Building Council (USGBC) released its report on a PVC avoidance related materials credit for the LEED Green Building Rating system. The report concludes that "no single material shows up as the best across all the human health and environmental impact categories, nor as the worst" but that the "risk of dioxin emissions puts PVC consistently among the worst materials for human health impacts."[41]
In Europe the overwhelming importance of combustion conditions on dioxin formation has been established by numerous researchers. The single most important factor in forming dioxin-like compounds is the temperature of the combustion gases. Oxygen concentration also plays a major role on dioxin formation, but not the chlorine content.Wikstrom, Evalena; G. Lofvenius,C.Rappe,S. Marklund (1996). "Influence of Level and Form of Chlorine on the Formation of Chlorinated Dioxins, Dibenzofurans, and Benzenes during Combustion of an Artificial Fuel in a Laboratory Reactor". Environmental Science & Technology 30 (5): 1637–1644. doi:10.1021/es9506364.</ref>
The design of modern incinerators minimises PCDD/F formation by optimising the stability of the thermal process. To comply with the EU emission limit of 0.1 ng I-TEQ/m3 modern incinerators operate in conditions minimising dioxin formation and are equipped with pollution control devices which catch the low amounts produced. Recent information is showing for example that dioxin levels in populations near incinerators in Lisbon and Madeira have not risen since the plants began operating in 1999 and 2002 respectively.
Several studies have also shown that removing PVC from waste would not significantly reduce the quantity of dioxins emitted. The European Union Commission published in July 2000 a Green Paper on the Environmental Issues of PVC. "[42] The Commission states (page 27) that it has been suggested that the reduction of the chlorine content in the waste can contribute to the reduction of dioxin formation, even though the actual mechanism is not fully understood. The influence on the reduction is also expected to be a second or third order relationship. It is most likely that the main incineration parameters, such as the temperature and the oxygen concentration, have a major influence on the dioxin formation”. The Green Paper states further that at the current levels of chlorine in municipal waste, there does not seem to be a direct quantitative relationship between chlorine content and dioxin formation.
As it resists degradation, waste disposal is an issue for products made of PVC. In the US, less than 1% of PVC was recycled in 1988.[7]
The European waste hierarchy refers to the 5 steps included in the article 4 of the Waste Framework Directive:[43]
In Europe, developments in PVC waste management have been monitored by Vinyl 2010,[44] established in 2000. Since June 2011, it is followed by Vinylplus, a new set of targets for sustainable development.[45] Its main target is to recycle 800,000 tonnes/year of PVC by 2020 including 100,000 tonnes of difficult to reycle waste. One technology for collection and recycling of PVC waste is Recovinyl[46] which reported the recycled tonnage as follows: pipe 25 kT, profile 107 kT, rigid film 6 kT, flexible cables 79 kt and mixed flexible 38 kT.
One approach to address the problem of waste PVC is through the process called Vinyloop. It is a mechanical recycling process using a solvent to separate PVC from other materials. This solvent turns in a closed loop process in which the solvent is recycled. Recycled PVC is used in place of virgin PVC in various applications: coatings for swimming pools, shoe soles, hoses, diaphragms tunnel, coated fabrics, PVC sheets.[47]
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.[48]
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