(January 31, 2014)
This article was updated in January 2014. See The PVC Debate: A Fresh Look for all-new interviews, data, and other information on PVC and other plastics.
Table 1. PVC use in building &
construction - 1992 (million pounds)
Polyvinyl chloride is one of our most common synthetic materials. Commonly known as “PVC” or “vinyl,” polyvinyl chloride is a tremendously versatile resin, appearing in thousands of different formulations and configurations. In the U.S. we produced over ten billion pounds of PVC resins in 1992. Among plastics, it is second in quantity only to polyethylene.
PVC is by far the most common plastic used in construction, where 6.3 billion pounds of resin were used in 1992. PVC
(the resin combined with various additives) turn up in applications as varied as sewer pipes, wire sheathing, flooring and weather-stripping (see table).
While some vinyl products such as siding and flooring have long had critics, recently the entire PVC industry has come under fire for environmental reasons. The loudest of these recent attacks are aimed not only at PVC but at the broader issue of chlorine use in industrial society. As reported in recent issues of EBN, Greenpeace is calling for the phase-out of all chlorine-based industries, including PVC, for a range of health and environmental reasons. Groups that are less political than Greenpeace have also spoken out against chlorine use, though not as strongly against PVC in particular. These include the International Joint Commission on the Great Lakes (IJC) and the American Public Health Association (APHA).
In the wake of all this publicity, many builders and architects are questioning the wisdom of specifying materials made from PVC and looking into alternatives. To make intelligent choices, however, especially in such a contentious debate, it’s useful to know some of the background.
PVC is comprised of chlorine, carbon, and hydrogen. The chlorine most often comes from a brine solution of common rock salt (sodium chloride). The chlorine is separated by electrolysis: a strong electric current across the liquid solution attracts sodium ions to the (negatively charged) cathode, while chlorine collects at the anode.
Until recently the electrolysis required the use of liquid mercury as the cathode, and traces of toxic mercury frequently contaminated by-products and liquid effluents. Most manufacturers no longer use mercury; however, in 1992 only 14% of U.S. chlorine production used mercury.
The most common chlorine separation process today, used in 77% of U. S. production, relies on a diaphragm in the electrolysis tank. A newer, membrane-based method is being adopted at all new facilities because it is both more energy-efficient and produces higher value by-products than the other systems. This membrane technology accounts for about 7% of chlorine production.
The PVC industry is the largest single consumer of industrial chlorine worldwide, using about 30% of all chlorine produced. The remainder goes into paper production, pesticides, pharmaceuticals, and a huge range of other products and processes. Some chlorine-based refrigerants and propellants (CFCs and HCFCs) are being phased out due to concern about their damage to the ozone layer.
In addition to chlorine, the electrolysis of salt creates caustic soda (sodium hydroxide), used in making soaps, paper, and rayon, and as a neutralizer in many other industries. While initially chlorine was an unwanted by-product of caustic soda production, demand for chlorine has increased so much that caustic soda has become relatively inexpensive, leading to its use in more and more processes.
PVC resin is 57% chlorine by weight. The rest is hydrogen and carbon, which are derived from fossil fuels: primarily natural gas and petroleum. Almost all PVC today is made from ethylene, which is the petrochemical of choice for many industrial processes. In the U.S. ethylene is made by cracking ethane in a reactor at about 800°C. (Ethane is a lightweight hydrocarbon that is extracted during the refining of natural gas.) Many of the by-products of ethylene manufacture (olefins, diolefins, and methane) are used in other industries. An older process of producing vinyl chloride by combining chlorine with acetylene, while no longer competitive with the ethylene-based process, is still used at one or two existing plants where the large infrastructure investment has locked the manufacturer into that process.
Ethylene and chlorine are combined to make 1,2-dichloroethane (EDC), which is then converted to vinyl chloride. Vinyl chloride, commonly referred to in the industry as VCM (for “vinyl chloride monomer”), is a gas at normal temperature and pressure. The by-product of converting EDC to vinyl chloride is hydrochloric acid.
EDC is made from ethylene and chlorine by two processes: direct chlorination, which uses pure chlorine; and oxychlorination, in which ethylene is combined with hydrochloric acid (see formulas).
The oxychlorination process takes place at higher temperatures and produces many more toxic by-products than direct chlorination; it is done primarily to utilize the hydrochloric acid by-product from the conversion of EDC to vinyl chloride.
PVC is produced by combining vinyl chloride into chains or polymers. Several different processes are used for polymerization, each of which gives the polymer different properties. By far the most common is the suspension process. Vinyl chloride is stirred into water, together with small amounts of methyl cellulose and organic peroxides, agents that initiate polymerization and keep the polymerized particles from conglomerating. The contents of the polymerization chamber have to be stirred vigorously throughout the six- to eight-hour process. In addition, the process must be cooled constantly, since it generates heat on the order of 660 Btus/lb of PVC. Cooling is accomplished by running water through the sides of the polymerization tanks, using about 30 gallons of water per pound of PVC produced.
The process is terminated when about 90% of the vinyl chloride has polymerized. Leftover vinyl chloride monomer is drawn off using a vacuum and largely recovered. Until recently, traces of vinyl chloride remained in the PVC material. The realization that vinyl chloride tended to leach into food or water from PVC containers, combined with the discovery that it is carcinogenic, have led to strict controls on the amount of residual vinyl chloride in PVC, especially containers for food and water.
To meet these requirements, PVC manufacturers have added a separate steam-stripping process to remove almost all residual monomer from the PVC. After the stripping, the PVC is in the form of small particles suspended in water. These are spun dry in a centrifuge and then air-dried before packaging.
Besides the suspension process, two other polymerization processes create PVC for certain applications. An emulsion process is used to produce finer particles of PVC, which are used for vinyl pastes—also called plastisols—from which some vinyl flooring is made. A mass process is simpler, though it is less flexible in terms of adding copolymers (other plastic resins mixed with the PVC to enhance certain properties). Mass polymerization accounts for about 20% of the PVC manufactured in the U.S.
PVC was first produced in a laboratory in 1872. It began to be produced commercially in the 1930s, when techniques for mixing it with plasticizers became known and PVC emerged as a substitute for rubber. During World War II, German scientists developed PVC pipe for water supply systems when material shortages limited conventional pipe supplies.
In the 1950s and 1960s many U.S. companies established facilities for polymerizing vinyl chloride into PVC. At that time the polymerization was done in open vats, requiring relatively little capitalization. High levels of worker exposure to vinyl chloride in the process were not considered hazardous, though they typically produced a narcotic effect. “We used to joke about getting a cheap high from it,” says Professor Rudolph Deanin of the University of Massachusetts at Lowell, who worked in PVC production during that period.
In 1971 a rare cancer of the liver, angiosarcoma, was traced to vinyl chloride exposure among PVC workers, and strict workplace exposure limits were established by the Occupational Safety and Health Administration (OSHA). These restrictions necessitated radical changes in the manufacturing environment— all polymerization vats had to be sealed and controlled. The cost of these changes and the increasing economies of scale enjoyed at larger plants eventually eliminated smaller producers, who either shut down their PVC production facilities or were bought out by the larger producers.
Today the North American PVC market is dominated by about a dozen large manufacturers. A few of these, such as Occidental Petroleum, Inc., operate facilities for all phases of the process, from chlorine and ethylene production to end products. Most, however, purchase some of the refined materials from other producers. Dow Chemical Company produces large quantities of vinyl chloride for sale to other companies but produces no PVC itself.
PVC resin alone is not all that useful. It mixes with additives relatively easily, however, lending a broad range of PVC compounds with various properties. Actual PVC resin often comprises only about 70% of PVC end-products and sometimes as little as 35% or 40%. The PVC may be mixed with other polymer resins during its production (copolymers), or any of a huge range of additives that are mixed in later. The most common additives include plasticizers, which give PVC the flexibility associated with many vinyl products, and stabilizers, which reduce its tendency to degrade under various conditions. The process of mixing these additives with the PVC is called
. Compounding may be done by the PVC manufacturers, by companies specializing in this process alone, or by the producers of end-products.
Plasticizers comprise a huge range of chemicals, mostly derived from fossil-fuel. They are used in all PVC products that require flexibility, such as electrical cables, hoses, gaskets, and vinyl sheet flooring. Plasticizers are used with other plastic resins as well, but the PVC industry consumes the vast majority (about 80%) of all plasticizers. While PVC is inherently fire-resistant because of its high chlorine content, the addition of plasticizers reduces this resistance and makes it necessary to add fire-retardants as well.
The most common traditional plasticizer is known as DOP or DEHP (for di-2-ethylhexyl phthalate). About nine million tons of DOP are produced annually worldwide. DOP was identified as a suspected carcinogen in 1987, and its use in medical blood bags was suspended when it was found to be leaching into the stored blood. There are also concerns about DOP released into the environment. The EPA’s Toxic Release Inventory (TRI) reports that over one million pounds of DOP were released into the air in 1991.
Stabilizers are added to PVC to reduce degradation, primarily from heat or ultraviolet light. The main chemical function of stabilizers is to prevent the formation of hydrochloric acid within the PVC (or absorb any that is formed), because the acid promotes degradation of the material.
Traditionally, heavy metals such as cadmium and lead were used as stabilizers. Due to concerns about the toxicity of these elements, the industry has been switching to alternatives for many applications. Nevertheless, a recent article in
reports that 15% of all the cadmium in municipal solid waste incinerator ash comes from PVC products. Lead also continues to be used in large-diameter pipes and in insulation for electrical cables (see page 15). Common replacements for these metals are calcium-zinc and barium-zinc formulations. Higher costs and technical difficulties are the reasons cited for not using these alternatives in all applications.
The list of other additive categories for PVC products is lengthy: processing aids, impact modifiers, pigments, inert fillers such as chalk, lubricants that aid in extrusion, flame retardants, smoke suppressants, biocides. These additives are generally used in much smaller quantities than the plasticizers and stabilizers, and most of them are also used in compounds based on other (non-PVC) plastic resins.
Table 2. Raw materials and energy consumed in the production of one metric tonne of PVC resin
1. Co-product credits assume some of the resources and energy can be attributed to the useful by-products of the process.
Table 3. Raw materials and energy consumed in the production of one metric tonne of PVC resin (by stage of production)
Resources consumed in the manufacture of PVC resin consist primarily of salt and fossil fuels as feedstock, and energy used in the processing. PVC production consumes less hydrocarbon than most plastics, which are almost 100% fossil-fuel derived.
Table 2 provides estimates of the resources and energy used in PVC production. As these figures apply to pure PVC, the resource consumption of end-products may differ greatly, depending on the additives used. Table 3 breaks down the energy and resource inputs according to the primary steps in the production process.
Table 4. Process-related emissions from production of PVC resin
Notes: The critical volumes data refer to amounts of water or air that would be contaminated to maximum allowable levels per the Swiss ministry. These data offer a means of comparing the relative significance of each type of emission.
Table 4 provides figures compiled by the Swiss Agency for Environment, Forest and Landscape (BUWAL) of emissions from the production of PVC.
These figures refer only to direct emissions from the manufacturing process, not to indirect emissions such as those from generating the energy used in the process. While some of the categories are too general to use for detailed pollution assessments, they do provide order-of-magnitude figures for the various emissions. These data refer only to the manufacture of PVC resin, not the additives which commonly comprise 20% to 50% of PVC products, and in some cases are another source of toxic contamination.
Most mercury emissions are from the mercury-based chlorine production process, which is gradually being replaced by newer methods. Nevertheless, concerns about mercury contamination have led to an international agreement in Europe calling for all mercury-based chlorine production to be phased out there by 2010.
Vinyl chloride was not considered particularly hazardous until the early 1970s, and emissions were not carefully controlled or monitored. After its carcinogenicity was discovered, however, vinyl chloride became one of just ten industrial substances to be controlled under the National Emission Standards for Hazardous Air Pollutants (NESHAP), which was superseded in 1990 by the Clean Air Act. According to the EPA’s toxic release inventory, fugitive and stack emissions of vinyl chloride in 1991 totalled just over one million pounds. Based on national production of 4.6 million tons, the rate of emissions was 0.22 lbs. of vinyl chloride per ton of PVC resin produced.
While there is no doubt regarding the carcinogenicity of long-term, high-level exposure to vinyl chloride, its health risk at lower exposure levels remains controversial. Industry representatives point out that prior to discovery of the cancers, PVC workers did not experience particularly negative symptoms or toxic effects other than light-headedness. Some studies, however, indicate that vinyl chloride may have a role in other cancers as well as possible birth defects.
Dr. Kenneth Rosenman of Michigan State University authored a 1988 study that found a correlation between birth defects of the central nervous system and exposure to ambient levels of vinyl chloride in communities adjacent to PVC factories. Asked about the many workers who were exposed to much higher vinyl chloride levels, Dr. Rosenman responds, “I’m not aware of any studies that have looked at reproductive effects among workers’ offspring.”
Vinyl chloride emissions are closely regulated and controlled, and yet large-scale releases do occur. The most common instance is when the polymerization process has to be terminated quickly due to operator error or power failure. Hilry Lantz of the Louisiana Department of Environmental Quality worked in PVC production at Georgia Gulf until last year. He describes how, during periodic power failures due to storms, they “had valve releases to control pressure. With no refrigeration you can’t control the pressure.” According to Professor Deanin of the University of Massachusetts, blowing out a whole batch of vinyl chloride is sometimes the only way to save a reactor. “If your power fails, the heat from the process could blow up the whole plant,” says Deanin.
More mysterious is the contamination of groundwater with vinyl chloride. In 1986 a lawsuit in Plaquemine, Louisiana ended with the relocation of an entire community adjacent to a Georgia Gulf PVC factory. All records were sealed as part of the settlement, but EBN spoke with Darrell Stevens of Ecology Consulting, who did environmental testing for the citizens‘ group. He reports having found “indoor vinyl chloride concentrations on the order of several hundred parts per billion” in people’s homes. Stevens attributes the vinyl chloride levels to contaminated groundwater running under the houses.
Some of the most serious allegations against PVC stem from the increasing evidence of long-term health and environmental damage caused by persistent organo-chlorines in the environment. These substances include dioxins, furans, and polychlorinated biphenyls (PCBs). There is convincing, though not definitive, evidence linking these toxins to increased breast cancer rates in women, lower sperm counts and reproduction-related birth defects in men, and a host of ailments affecting wildlife, particularly species high on the food chain. Much of the concern is focussed on disruption of the endocrine system, because severe health effects are likely even at very low levels of exposure to the toxins.
An April 1993 report from the European Council of Vinyl Manufacturers acknowledges that certain dioxins are formed when hydrochloric acid is mixed with ethylene to form EDC (oxychlorination). According to Ronald Cascone, a researcher at Chem Systems, Inc. of Tarrytown, New York, these dioxins are not of concern, as they appear in minute quantities among a range of other toxic substances, all of which must be handled appropriately. Focusing only on the dioxins “is like picking the fly-specks off of horse-dung,” says Cascone. Toxic wastes, including dioxins, appear in the crude EDC, in wastewater from the reaction, and in gases emitted from the reaction. According to the European report, all three of these sources are now carefully controlled, with nearly all the toxins destroyed by incineration and other means.
Having just completed a detailed survey of the industry for the Vinyl Institute, Cascone feels confident that on the whole these toxic wastes are treated appropriately. Cascone himself designed a system that is in use at two facilities to convert some of these wastes into dry-cleaning solution by combining them with additional chlorine.
Dioxin quantities are commonly measured by their toxic equivalents (TEQ) relative to the most toxic form, 2,3,7,8 TCDD. While the European report acknowledges that even with all the controls in place, minimal dioxin releases continue, other observers agree with Cascone that PVC manufacture is not a significant source of dioxin contamination. According to Dr. Len Ritter of the Canadian Centre for Toxicology, the real culprits are persistent pesticides (most of which are now banned in the U.S., but whose effects are still being felt), and chlorine emissions from the pulp and paper industries. “I’d be very surprised if it were determined that [the PVC manufacturing] process was implicated in this problem,” says Ritter. “[Vinyl chloride] monomer was recognized as a human carcinogen years ago and has been subject to extraordinary regulation since then. Chlorine use in pulp and paper, on the other hand, continues to go largely unregulated, and there are orders of magnitude difference in the emissions.”
A 1989 Danish study reported that doubling the amount of PVC led to a 34% increase in dioxin formation. In a 1987 study in Pittsfield, Massachusetts, however, increasing PVC concentrations caused no corresponding increase in dioxin emissions. Chlorine found in wood and paper may contribute just as much to dioxin formation as that in PVC, according to some researchers. Dioxin formation is affected primarily by the incinerator’s operating conditions. A 1986 Swedish study found that the emissions of certain persistent organo-chlorines could be reduced to 2% of their original level just by optimizing the turbulence and air-flow within the combustion chamber.
Dioxins are created when PVC is burned under less-than-ideal conditions, as in building fires. Ash from fires in PVC warehouses and factories contains dioxin at levels ranging from several to several hundred parts per billion. While isolated incidents of exposure to dioxin may not be a serious health threat to fire victims, such fires can contribute to environmental contamination.
One of the major areas of controversy surrounding PVC in building products is the potential toxicity of the material when it burns. Some have argued that the added danger from PVC in fires is serious enough that we should be keep it out of buildings, while the industry insists it poses no unusual fire hazard. No one disputes that hydrochloric acid and a wide range of other toxics are released when PVC burns. Just how much hydrochloric acid humans can breathe without injury is hotly debated, however. Furthermore, the biggest danger is from decomposing PVC, which releases toxins
it starts burning, and can go unnoticed for a time. “Talking about its [PVC’s] combustibility is grossly misleading,” says Deborah Wallace, a project leader with public service projects at the Consumers Union.
Decomposing PVC is a problem in particular with wiring, which frequently overheats for a long time before it ignites. As the temperature rises further, phthalate plasticizers (such as DOP) give off phthalate anhydride, according to Wallace, which is a heart toxin. After wiring, the most problematic PVC product is wallcoverings, which tend to separate from the wall and quickly decompose at relatively low temperatures. Wallace believes that fire protection codes are too focussed on one type of fire. “They have fixated on one scenario, of fire starting in open space,” she said. As a result, the danger of PVC wiring and plumbing decomposing in walls is not given adequate attention. In response to a “Fact Sheet” from The Vinyl Institute claiming that not one death in the U.S. has been linked to PVC, Wallace lists several autopsies that specifically identified PVC combustion as the cause of death.
At the end of their useful life, products made of PVC pose additional problems. Recycling post-consumer PVC products is difficult because of the wide range of additives and formulations that go into them. Marty Forman of PolyAnna Plastics, Milwaukee, Wisconsin, recycles PVC scraps from a window manufacturer. While he sees no problem with recycling the clean industrial waste, he acknowledges that post-consumer products are a problem. “Some companies buy the dirty bottles, but they lose money on every pound they take. They’re doing it to be a part of the recycling effort,” Forman claims.
Aware of PVC’s poor reputation with recycling, The Vinyl Institute has launched a campaign to encourage recycling and increase awareness of recycled vinyl products. As a result, recycling of PVC is increasing rapidly, though it still lags far behind other common plastics. The industry is also promoting incineration with energy reclamation, which it calls “thermal recycling,” even though the heat content of PVC is much less than that of most other plastics.
Except for the space taken up, landfilling PVC is not usually a problem. Attesting to the stability of PVC in landfills is the fact that most landfill liners are made from PVC. In some cases, though, the additives in PVC can make the waste materials hazardous. Electrical wires are commonly shredded to recover the metals, leaving the PVC material, known as “fluff.” Enough lead leaches out of this fluff (from the stabilizer) that it is now handled as hazardous waste, making it expensive to get rid of. Researchers at Geon Company (formerly BFGoodrich’s vinyl division) are experimenting with ways to recycle the fluff into traffic cones, as an alternative to disposal.
PVC is not only difficult to recycle, it also greatly complicates the recycling of other plastics, particularly polyethylene terephthalate (PET). Clear PVC containers are very difficult to distinguish from those made of PET. During processing the PVC melts at much lower temperatures than the PET and actually starts to burn when the PET is melting. The burnt PVC creates black flecks in the otherwise clear PET material, making it unusable for many applications. Even worse, it can seriously damage the equipment. “PVC becomes hydrochloric acid in the machinery, and it can eat the chrome plating off the machines,” explains Forman of PolyAnna Plastics. Since even a tiny amount of PVC can do expensive damage, optical scanners and other high-tech devices have to be installed at many PET recycling facilities to separate out unwanted PVC containers.
The fact that PVC turns into hydrochloric acid as it burns causes trouble for the incinerators as well. While smokestack scrubbers trap enough of the acid that it is not a serious environmental threat in itself, the acid damages both metal and masonry surfaces in the incinerators, necessitating increased maintenance and replacement of parts. This problem is serious enough that a Japanese company, Calfa Chemical Co., has just introduced a new PVC additive with the sole purpose of reducing hydrochloric acid formation upon incineration of PVC.
PVC piping, first introduced in 1952, is the largest single market for PVC in the United States. More than 3.6 billion pounds of PVC resin were used in piping in 1992 in the U.S., nearly 60% of total PVC used by the building industry. According to the Uni-Bell PVC Pipe Association, “more than 90% of all wastewater sewers being installed [in the U.S.] are made of PVC, and over 70% of all potable water distribution pipes (≤ 12”) are PVC products.” In residential construction, PVC holds a much smaller but still significant market share of hot/cold water piping and drain/waste/vent (D-W-V) piping.
PVC pipe is made with an extrusion process, and pipe fittings are made by injection molding. PVC pipe diameters range from 1/8” to 36”. For pipe that will be used for higher temperature applications or where fire exposure is a concern, such as hot and cold tap water piping and sprinkler systems, a slightly different form of PVC known as CPVC (with an extra chlorine in the polymer chain) is generally used.
Compared with many other applications, the PVC compound used in pipes and fittings is relatively pure: 70% to 95% PVC resin by weight, according to the Uni-Bell PVC Pipe Association. By far the most common additive (up to 20% of the PVC compound) is a simple filler, usually calcium carbonate, that reduces manufacturing cost, stiffens the melt and can provide various strength properties. Other common additives, comprising a fraction of a percent up to 1% or 2%, include heat stabilizers, UV screens, pigments, impact modifiers, and lubricants. Because the pipe needs to be rigid, plasticizers—the most significant additives in many other PVC products—are not added.
So how does PVC compare with other piping materials in use today?
That depends on whom you talk to. The PVC industry will tell you that nothing is better. Indeed, PVC’s light weight, high strength-to-weight ratio, corrosion resistance, durability, low cost, and easy installation are hard to ignore. But PVC is not the only game in town, and for certain uses, other pipe materials have some definite advantages over PVC. Other common materials used for pipe manufacturing are compared with PVC below.
Widely used for waste-drain-vent pipe in houses, ABS or acrylonitrile-butadiene-styrene offers few if any advantages over PVC. ABS resin is lighter than PVC but energy-intensive to produce and more than twice as expensive (as a resin). ABS also has nearly twice the thermal expansion of PVC, and its chemical components, while perhaps not as damaging to the environment as PVC’s, are hardly innocent bystanders, either.
Because ABS pipe must be cost-competitive with PVC even though the resin is a lot more expensive, profit margins in ABS pipe manufacturing are smaller. This leads to cost-cutting shortcuts and material substitutions by manufacturers—sometimes with terrible results. Substitution of low-grade recycled ABS resin for virgin resin by a handful of ABS pipe manufacturers on the West Coast during the 1980s is resulting in catastrophic failure of piping in thousands if not hundreds of thousands of houses.
High-density polyethylene (HDPE) is the least expensive, lightest, and most flexible of the plastics used in piping. Its manufacture from natural gas and crude oil is fairly simple, and the resin can be more easily recycled than almost any other plastic. The ability to manufacture it in long continuous coils rather than short straight sections makes it the material of choice for many buried natural gas and water supply piping applications. For municipal water and sewer systems, it is the preferred material for “trenchless piping,” in which special equipment is used for tunneling a pipe under a highway or from supply mains to a house without having to dig trenches. Polyethylene also lends itself to the highly appropriate practice of relining older, failing concrete, clay tile, or asbestos-cement pipes.
Unfortunately, HDPE has the greatest expansion coefficient of any plastic pipe material, almost three times that of PVC (and 24 times the expansion of vitrified clay pipe)—a property that causes all sorts of problems in applications where temperature fluctuation is common, such as waste piping. HDPE is commonly used in perimeter drain pipe around foundations, but rarely inside houses. A European type of flexible laminated polyethylene piping with a thin layer of metal may soon be accepted for wider use as hot/cold water piping in houses. The composite nature of this piping, however, will make recycling difficult.
. Cast-iron drain pipe is still required by plumbing or fire codes in some areas. Certain organizations with a vested interest in the high amount of labor required in installing cast-iron pipe, such as the California State Pipe Trades Council, have lobbied state legislatures and code officials to slow or block the transition away from cast iron. Cast iron is a durable material, but no more durable than PVC. It has a very low coefficient of thermal expansion (about one-fifth that of PVC). In waste piping, the sound-deadening properties of cast iron also provide some advantage over plastic. On the down side are its heavy weight (four times that of PVC for 4” pipe), its high embodied energy (see table), greater labor cost for installation, and corrosion on the inner surface of the pipe that can lead to failure or restrict flow.
Vitrified clay pipe is the grandfather of the piping industry. There are vitrified clay pipes in use today that are over 170 years old and still in perfectly good shape, according to the National Clay Pipe Institute, which represents seven manufacturers. The expected service life is commonly given as 100-plus years—more than twice that of pipe made from any other material—and several manufacturers offer 100-year warranties.
While clay pipe has seen most of its market share lost to PVC over the past 30 years, there are applications where clay is still the best—and sometimes the only—choice. Fired to 2,000°F to create a smooth, chemically resistant, and highly durable surface, vitrified clay pipe has the lowest thermal expansion coefficient of any pipe material and is extremely resistant to chemical reaction and general wear. These properties make it the only acceptable piping material for many industrial applications, and in a few urban areas it is the only permitted material for sewer pipes. The down side to vitrified clay pipe is its weight (greater than cast iron for 4” pipe), high labor costs for installation, and limited availability in many areas (plumbing supply stores may tell you it isn’t even produced any more). Despite the heavy weight, the embodied energy of clay pipe is lower than that of any comparable piping.
Vinyl siding was introduced in the early 1960s, but did not gain much attention until the 70s. During the 80s and 90s, its use has increased dramatically. Since 1986, its use has doubled, reaching 2.2 billion square feet in 1992. Siding is the second largest market for PVC resin, with 1 billion pounds used in 1992 by about about 20 manufacturers.
While vinyl siding was initially sold almost exclusively for remodeling, today more than a third of vinyl siding is used in new construction.
Vinyl siding is manufactured by coextrusion: two layers of PVC are laid down in a continuous extrusion process. The top layer (weatherable capstock), which comprises about a third of the siding thickness, includes about 10% titanium dioxide, which is a pigment and provides resistance to breakdown from UV light. The lower layer (substrate) is typically about 15% calcium carbonate, which balances the titanium dioxide to keep both extrusion streams equally fluid during manufacturing. A small quantity of tin mercaptan or butadiene (less than 1%) is added as a stabilizer to chemically tie up any hydrochloric acid that is released into the PVC material as the siding ages. Lubricants are also added to aid in the manufacturing process.
Vinyl siding has a mixed reputation in the building industry. It has often been considered a cheap substitute for wood, yet it is favored in some markets because of its lower maintenance requirements—it does not need to be painted or stained as does wood. It does change in appearance as it ages, however. Yellowing, bleaching, and “chalking” all occur as a result of rather complex chemical changes brought on by exposure to heat, UV light, and moisture. Somewhat surprisingly, yellowing occurs to a greater extent in wetter northern climates than in the arid, sunny Southwest, according to a recent article in the
Journal of Vinyl Technology
. Vinyl siding will also become somewhat more brittle over time, though most manufacturers provide a lifetime warranty on their products.
In terms of cost, vinyl siding ranges from $120 to $170 per square (installed cost), according to a recent article in
Plastics in Building Construction
. That is comparable to hardboard and plywood siding, but significantly less than other options such as aluminum ($180 to $300/square), pine ($275/square), or cedar ($350/square) (prices as listed in the article).
A higher priced, but more wood-like,
vinyl siding is reportedly just around the corner. This will be a thicker, co-extruded product that looks and feels more like wood. Some industry experts predict that such a product may capture a “double digit share of the market within a year after introduction,” according to the May 1993 issue of
. Even though the density of this foamed PVC siding (.50 - .59 grams/cc) would be significantly less than that of solid vinyl siding (1.45 g/cc), the greater thickness of the foamed product would result in two to three times as much PVC material use per square foot of siding.
From an environmental standpoint, vinyl siding offers advantages of avoided air pollution that results from painting or staining wood and hardboard siding. It is less energy intensive than aluminum siding but also less recyclable. Vinyl siding can be recycled, but current technology permits recycling only of new vinyl (factory scraps and job-site cutoffs), not old siding removed during remodeling or demolition. At least two companies produce vinyl siding with (pre-consumer) recycled vinyl, according to the Vinyl Institute.
Because of its significantly greater material use (and the environmental impacts relating to PVC production) cellular vinyl siding will be less attractive environmentally than the present solid vinyl siding. Locally milled pine or spruce siding, and various composite siding products with recycled fiber content, may be preferable to vinyl, despite the greater maintenance requirements.
Approximately 420 million pounds of PVC resin were used in 1992 by the wiring industry. PVC is used both as the insulation around individual wires and as the sheathing around a bundle of insulated wires (as in Romex wiring). PVC for this application is compounded with a fairly high percentage of plasticizer (to provide flexibility) and 2% to 6% lead stabilizer, such as lead silicate sulfate or lead phthalate. The stabilizer bonds with free chlorine that is released over time, producing lead chloride. Lead chloride is one of the only chlorine salts that is not soluble in water, according to Tom Williams, a technical service manager at Geon Company, so the wire insulation or sheathing can maintain its electrical insulation properties even when wet.
While the lead compound imparts necessary electrical insulation properties to the wire or cable, its presence can be environmentally detrimental. Not too many years ago it was common practice to burn wire removed from buildings to recover and sell the copper. Such a practice produces smoke from the PVC that would be not only acidic and potentially toxic, but also a source of lead toxicity.
The primary health concern with wire sheathing has to do with fire. Although the chlorine in PVC tends to suppress fire, once it does burn, dangerous chemicals are generated (from the plasticizers and other additives as well as the PVC). In electrical fires, wire sheathing is often the first material to burn. Several prominent subway fires in recent years have lead to new regulations regarding wire and cable in those applications. Such a fire in the London Underground resulted in a total ban of halogenated cables there (i.e., all sheathing that contains chlorine), according to the March 1993 issue of
, and a fire in the New York City subway system lead to new requirements for low-smoke sheathings in certain city applications.
Fire concerns have lead to developments on several fronts. New low-smoke PVC sheathings with long-chain or polymeric plasticizers are available, as are low-acid PVCs with fillers that absorb any free HCl. On another front, halogen-free, low-smoke polyethylene compounds are gaining market share in commercial wiring. Some of this is a result of increasing restrictions on use of wiring with halogenated sheathing, particularly in Germany and a few other European countries. Wire and cable sheathing without halogens is a lot more expensive, though. With residential wiring, the upcharge for non-PVC-sheathed wire could be 250%, according to
. There is also some shift to linear, low-density polyethylene (LLDPE).
Of the 2.6 billion square feet of vinyl flooring shipped in 1992, 61% was for sheet vinyl and 39% tile, according to the Resilient Floor Covering Institute. Sheet vinyl flooring is produced by a “calendering” process in which a layer of PVC compound (PVC resin with plasticizers and other additives such as fungicides) is applied over a backing material—usually an organic fiber such as paper or a foamed plastic material. Vinyl tiles are produced usually by injection molding or dispersion coating. Because they do not need to be flexible, plasticizers are generally not needed, though other additives are.
In 1992, 66% of vinyl flooring was used in residential buildings, 34% in commercial. A 1991 survey conducted for the Resilient Floor Covering Institute showed that vinyl is the dominant type of flooring in residential kitchens, with 73% of the total market (compared with ceramic tile at 7%, carpeting at 10%, and wood/other at 9%). In bathrooms, vinyl flooring was found in 47% of homes, compared with ceramic tile (28%), carpeting (24%), and wood/other (17%).
Relative to the environment and indoor air quality issues, vinyl flooring has little to boast about. Along with the “upstream” concerns about PVC and the various additives, vinyl flooring can offgas chemicals, most vinyl flooring is installed with adhesives, and at the end of its useful life recycling is difficult or impossible.
For several weeks or months after installation, offgassing from flooring adhesives can be hazardous to building occupants. And the VOCs emitted by conventional adhesives contribute to air pollution. Progress is being made with adhesive formulations, however. Many new low-VOC and zero-VOC adhesives have been entering the market. These should reduce risk both to indoor air quality and to the environment.
There are a few recycled vinyl flooring products on the market. Oscada Plastics, Inc. makes both vinyl tile and sheet flooring out of 100% recycled vinyl, according to sales manager Ken Szabo, though their decorative vinyl floor tile includes a wear layer of virgin PVC. Their recycled vinyl sources include auto companies and vinyl scraps from their parent roofing film company. The company does not use sheet flooring as a source of recycled vinyl because of the backings.
As for what happens at the end of its life, sheet vinyl is far less recyclable than vinyl tiles because of the plasticizers and its composite nature (several layers of different materials). Even tiles often have non-vinyl backings that impede recycling. For these reasons, flooring is a PVC building application where shifting to alternate materials should be a high priority. One of Europe’s largest vinyl flooring manufacturers is already doing just that. The Swedish-German Tarkett Group, which uses 176 million pounds of PVC per year, announced in late 1993 that it would begin a gradual shift from PVC to polyolefin-based resins. As reported in
(September 1993), the company cited environmental pressure for the change.
Alternatives to vinyl flooring offer both advantages and disadvantages:
is produced from natural clays, is more durable than vinyl if properly installed, can be laid with non-offgassing portland-cement-based grout, can serve as heat storage in passive solar buildings, and requires almost no maintenance. Additionally, ceramic tiles are available that are made out of such recycled materials as feldspar tailings, auto windshields, and old fluorescent light bulbs. On the down side, ceramic tile produces a surface which can be hard on the feet, and it is more expensive to buy and install.
of concrete or stabilized earth can be very inexpensive and, like ceramic tile, serve to store heat for passive solar heating.
can also be low cost, especially if installed directly over the subfloor. But most carpeting offgasses potentially hazardous chemicals, usually has a shorter lifetime than vinyl, requires the use of underlayment, is often glued down, and is as difficult to recycle as sheet vinyl flooring. Plus, carpeting provides an ideal environment for promoting biological indoor air pollutants (molds, fungi, dust mites, etc.).
can be a very appropriate flooring material, particularly if locally milled hardwood is used from sustainably managed forests. Wood is more expensive than vinyl, though, and must be periodically refinished to keep it looking good. While new water-based polyurethane varnishes are available, most varnishes and other floor finishes still emit large quantities of VOCs. Some wood flooring is made by laminating hardwood veneers onto OSB or other manufactured wood substrates.
Cork and linoleum
flooring products are available from specialty suppliers and are very attractive environmentally. Natural linoleum has been made for generations and is a mixture of linseed oil, cork, wood dust, and dyes. Cork flooring is available in tiles composed of compressed cork chips, but check the products carefully, because some are essentially vinyl flooring with the cork substituting only for the plastic foam layer.
Approximately 280 million pounds of PVC resin were used in vinyl window manufacturing in 1992. Just under half of the vinyl used in windows (130 million pounds) was for all-vinyl window extrusions (called profiles); the rest was for vinyl cladding over wood windows. The American Architectural Manufacturers Association (AAMA), which tracks window manufacturing, reported that residential all-vinyl window production in 1992 totalled 8.6 million units, 22.6% of total window production. All-vinyl windows comprise 35% of the replacement window market, while they hold just under 10% of the new construction market. Since 1986, all-vinyl window production has increased more than 100%, while total window production has increased just 3%. In new construction, the use of all-vinyl windows has grown by 800% during the same period.
So how do vinyl and vinyl-clad windows stack up with other materials in terms of the environment? As cladding, vinyl—which does not require painting—offers the benefit of low maintenance over natural wood, though some new factory paint finishes have improved in durability considerably in recent years.
Solid vinyl windows have been promoted for their durability, but studies done for the Canada Centre for Mineral and Energy Technology call into question some of those claims. The study
Long Term Performance of Operating Windows Subjected to Motion Cycling
found that air leakage through the vinyl casement windows increased 136% (significantly more than the aluminum and fiberglass windows tested, and somewhat more than the wood windows tested). “Visual inspection revealed that unreinforced PVC profiles are subjected to distortion,” concluded the report, adding that this is caused by “the lack of rigidity and the high coefficient of linear expansion of sash members.” Because of the construction of vinyl windows, strength is highly dependent on the extrusion design, and the Canadian study included only a few vinyl windows out of the hundreds that are produced.
Vinyl is projected to garner a growing share of the window market in coming years, according to AAMA. One of the reasons is reduced availability of the old-growth wood that has long been prized by wood window manufacturers. To date, most of the growth in vinyl window production has been at the expense of aluminum windows, but window manufacturers who have traditionally used wood are expected to turn to vinyl as well as other materials for replacing clear pine and fir. In fact, this is one of the building technology areas where we can expect to see the most change over the next ten years. Exactly what role vinyl plays in that transition will depend in part on how accepting users are of vinyl’s environmental record.
Ray-Core's PVC joining system for foam-core panels.
In addition to the applications covered above, vinyl is used in countless smaller building applications. It is also beginning to see use in structural building components.
Ray-Core, Inc., a foam-core panel manufacturer in Lock Haven, PA, is using vinyl extrusions (from post-industrial recycled vinyl) for a unique panel-edge/spline-joint system. Extruded vinyl “studs” at the panel edges are molded into the isocyanurate foam during manufacturing. During installation, a tubular vinyl spline is used to join panels (see illustration).
Going far beyond Ray-Core is Royal Plastics Group of Weston, Ontario. The largest PVC extruder in North America, Royal Plastics has developed an entire vinyl housing system with snap-together modular wall and roof panels. Wall panels are designed to be filled with concrete. The system includes other vinyl components , such as vinyl windows and decorative vinyl exterior wall facings in imitation brick, stone, and wood. John Garbin of the company said that the company expects to receive necessary code approvals in the U.S. in about 12 months and is already “very active off-shore.” According to various articles about Royal Plastics, the company has big plans for their housing system. The idea is to produce very small, low-cost units that will find large markets in Third World countries. The company is expected to build three or four plants annually outside of Canada in coming years, each of which could produce 18-20,000 houses per year.
At this point, we are left with more questions than answers. So what does all this mean? Is the PVC phase-out called for by Greenpeace justified? What would be the economic implications of such a phase-out? Greenpeace and the International Joint Commission on the Great Lakes have responded to significant environmental problems resulting from a class of industrial compounds with a call for their elimination. There is merit to addressing the problem of chlorine-related pollution and health problems in a broad manner as they are doing. One cannot ignore the million-plus pounds of vinyl chloride gas or the million-plus pounds of the plasticizer DOP emitted into the atmosphere each year. Or the 15% of cadmium emissions from municipal solid waste incineration that comes from PVC products. Or the evidence (controversial though it may be) linking PVC production and disposal to dioxin, PCB, and furan emissions.
To the credit of the chlorine and PVC industries and government regulatory bodies, however, vast improvements have been made in manufacturing processes over the past twenty years, and many of the worst environmental offenders (DDT, dieldrin, and CFCs, for example) are already gone or on their way out. The residual vinyl chloride gas in PVC products has been reduced to (perhaps) insignificant levels, compared with two decades ago. The environmental and health risks associated with PVC are greatest at the two ends of its lifetime: during manufacturing and disposal (if by incineration). Most PVC products are safe to use and some offer significant durability, cost, and maintenance advantages compared with competing products.
Concerning the costs of a chlorine phase-out both Greenpeace and the chlorine industry have exaggerated or blatantly misled the public. An often-quoted report by the Charles River Associates (CRA), which was commissioned by the Chlorine Institute, estimates the cost of eliminating chlorine to be $102 billion per year in higher product costs. A cursory look at these cost estimates shows that half of all chlorine use could be eliminated for $4 billion per year and 96% of the chlorine could be phased out for $18 billion per year. $53.6 billion of the $102 billion CRA total is attributed to the cost of eliminating chlorine from pharmaceuticals (representing just 1.3% of chlorine use), which no party has explicitly suggested.
For builders and architects, our recommendation is not to avoid vinyl altogether, but to seek out better, safer, and more environmentally responsible alternatives. Also, keep an eye on the PVC debate. A process has been put into motion that will take many years or even decades to unfold. Newer, safer, materials will almost certainly be developed by industries that are increasingly aware of environmental concerns. It is hoped that this article will provide the background needed for you to understand this debate as it unfolds and to make changes in your design or construction practice when it makes sense to do so. We’ll keep you posted.
For more information:
Uni-Bell PVC Pipe Association
2655 Villa Creek Drive, Suite 155
Dallas, TX 75234
National Clay Pipe Institute
P.O. Box 759
Lake Geneva, WI 53147
Royal Building Systems, Ltd.
Royal Plastics Group
4301 Weston Road, Suite 200
Weston, ON M9L 2Y3 Canada
The Vinyl Institute
Division of The Society of the Plastics Industry, Inc.
Wayne Interchange Plaza II
155 Route 46 West
Wayne, NJ 07470
Resilient Floor Covering Institute
966 Hungerford Dr., Suite 12B
Rockville, MD 20850
Greenpeace Chlorine Campaign
16 North Boylan Ave.
Raleigh, NC 27603
Canada Centre for Mineral and Energy Technology
Energy, Mines and Resources Canada
562 Booth St., 9th Floor
Ottawa, ON K1A 0E4
January 1, 1994
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