All About PVC: Applications, Recycling, and Safety Information
Polyvinyl chloride (PVC) is just one of those rare materials that are as popular as they are controversial. Despite how long PVC has been used across various industrial and household applications, the issue of its safety is still hotly debated until today. So far, there hasn’t really been a convincing conclusion to the debates on whether the manufacturing or recycling process of PVC is sustainable, or if you should be using PVC at all.
What are the reasons behind this massive, unending conflict? In this article, we look at all the scientific information on PVC so you can come up with your own informed decision on the matter.
What is PVC?
Polyvinyl chloride, more colloquially known as vinyl, is a synthetic polymer that is composed of carbon, hydrogen, and chloride in its pure form. It was first synthesized in 1872, and how holds the distinction of being the third most common synthetic polymer product right behind polyethylene and polypropylene. PVC is merely a white powder in its pure form but can be enhanced with various additives that alter its characteristics, allowing it to be worked into different objects with varied physical and chemical properties.
How is PVC manufactured?
To fully understand what makes PVC so controversial, we need to know how this material is produced. The backbone for the PVC polymer is composed of numerous vinyl chloride monomers. The stock compound used to produce PVC is usually naphtha or ethylene, both of which are hydrocarbon compounds derived from petroleum products.
In regions where there is a substantial supply, coal has also been used as a starting material for PVC production. However, the calcium carbide process that converts coal to acetylene, which is then converted to vinyl chloride, is much more energy intensive and generates more waste.
Forming a polymer from a solution of vinyl chloride requires a chain reaction that will bind the monomers to each other and form a long-chain structure. This is done by adding an initiator compound, commonly dioctanoyl peroxide or diacetyl peroxydicarbonate. This chain reaction proceeds to form very long PVC chains, often with molecular weights ranging from 45,000 to 64,000 atomic mass units.
When the reaction has stopped, the resulting slurry is degassed to remove excess vinyl chloride and centrifuged to remove water. The slurry is then dried at high temperature to produce the characteristic white powder from which all PVC products are manufactured.
However, unmodified PVC is hardly useful for most commercial and household applications. Through the introduction of additives, PVC can be improved by enhancing its heat stability, impact resistance, UV resistance, flame resistance, and biological suppression. One of the most common additives used with PVC is phthalic acid, a plasticizer hat greatly improves the material’s flexibility and workability.
Why is PVC so popular?
PVC has become a highly popular material due to its sheer versatility. Depending on the additives used, PVC can either be rigid or flexible. As a material for construction, modified PVC has very a high hardness and elastic modulus. It is also a relatively lightweight material compared to wood or concrete panels.
Probably the most popular use of PVC is in pipes for household drainage, gutters, downspouts, and drain pipes. In fact, about half of the world’s PVC can be found underground – buried for municipal water supply and sewerage systems. PVC has the useful characteristics of being inert against chemicals, sunlight, and oxidation from water, making it an affordable and lightweight material for piping.
In the US, the PVC used for municipal water supply is a modified form called chlorinated PVC (CPVC). Although this material has already been approved for transmission of potable water supply since the 1980s, it was only approved by the California Building Standards Code in 2007 for use in residential systems. CPVC is considerably more flexible and has better thermal stability than standard PVC.
PVC can be modified to achieve a variety of finishes, making it an aesthetically pleasing alternative for household fixtures. With its added benefit of being weather-proof, PVC has quickly become popular for replacing painted wood in window frames and sills. Pre-fabricated PVC sheets have also been used for convenient installation of wall claddings and fascia in modern homes. Flexible PVC flooring can be found in practically all hospitals, offices, and schools due to its smoothness, strength, ease of application, and affordability.
The workability and affordability of PVC have also made it a popular material for commercial signage products, including stickers, outdoor road signs, and car racing stripes. Being weather-proof, PVC signs do not deteriorate quickly when exposed to natural elements. Plasticized PVC is commonly used for these applications, as it can be easily cut, expanded, and printed on.
Although the heat and electrical insulation of PVC is inferior compared to other plastics, plasticized PVC remains a fairly popular material for coating of wires and cables. In the past, PVC for these applications have been stabilized with lead, but these have been almost completely phased out in favor of calcium-based alternatives.
PVC is also a highly-used material in the healthcare industry, accounting for about a third of all plastic-based medical devices. Due to flexible PVC being lightweight, transparent, biocompatible, and sterilizable, it has become one of the most preferred materials for containers and tubing for blood and blood components, urine collection, and catheters.
Is PVC recyclable?
PVC is considered a recyclable material, but the recycling process for PVC is made a little more complicated by two critical factors: the high chlorine content of raw PVC and the number of different and potentially hazardous additives uses for commercial PVC. This means that PVC has to be separated and treated differently from other recyclable plastics. Depending on the source of the PVC product, there are two methods by which it can be recycled.
In mechanical recycling, the PVC is merely shredded into very small particles. These particles, called recyclates, are then melted and remolded into different products. Although this process is fundamentally simple, any variations in the types of PVC products being recycled tends to make the results of mechanical recycling unpredictable. Since there are no chemical reactions involved in this process, the results can be a mish-mash of the characteristics of both flexible and rigid PVC products. For these reasons, mechanical recycling is usually reserved for post-industrial PVC waste with more uniform composition.
The second method to recycle PVC is called feedstock recycling. Using a series of chemical processes including pyrolysis, hydrolysis, and heating, recyclable PVC products are converted into their base chemical components. This is a mixture of the hydrocarbons from which PVC was made from along with various additives such as heavy metals and several types of salts. These components can be separated and either reprocessed to create new PVC or burned as fuel for energy.
Due to the complexity of recycling PVC, it has become the least post-consumer recycled plastic per usage amount in the US. According to estimates by the Environmental Protection Agency, less than 1 percent of the 910,000 tonnes of PVC waste generated is recovered for recycling. This discrepancy creates a lot of unnecessary waste, as many experts believe that PVC can be recycled roughly seven times and still retain satisfactory physical and chemical properties.
Which components in PVC are toxic?
There is no doubt that PVC is highly useful, and a majority of professionals in the infrastructure, construction, and healthcare industries can attest to its reliability. However, the controversy surrounding PVC has always been about its image as one of the most “polluting” plastics. Given the scale of PVC use worldwide, the possibility that PVC is a potent pollutant is indeed alarming. Does PVC deserve such a reputation? What are the compounds in PVC that environmentalist consider harmful?
Untreated PVC is natural rigid, so plasticizers need to be added for applications that require more flexible or malleable PVC. About 70% of the plasticizers used in the US are composed of phthalates or the ester form of phthalic acid. Aside from plastic product such as PVC, phthalates can also be found in detergents, adhesives, personal care products, waxes, and paints. Phthalates can even be found in certain foods, particularly in fatty fare such as meats, milk, and butter.
Phthalates are so ingrained into everyday human life that a study conducted by the Center for Disease Control and Prevention has shown that metabolites of phthalates can be found in the urine of most Americans. They are easily released into the environment and are present in high concentrations in both air and water. They do not degrade easily through biological or chemical means.
So, the point is that there are probably phthalates coursing through your body, in the air you breathe, and in the water you drink. The real question is: are phthalates harmful to us or the environment? Unfortunately, after more than four decades of study, no one has come up yet with a conclusive answer to this question. Most studies on phthalates have only been able to determine their effects on animals, which cannot be reliably associated with their effects on humans.
Answering whether phthalates are dangerous or not is made complicated by the fact that there are so many of them. Certain phthalates – DBP, BBP, and DEHP – have been found to cause reproductive system developmental problems or cancers in lab rats and as such, have been banned from toys and products intended for children. Other phthalates, including DiDP and DnOP, have been shown to cause skin irritation in both humans and animals but have not been subjected to as much scrutiny as the previous examples.
It doesn’t provide much assurance, but there has been no study that can prove that phthalates are harmful to humans. If it gives you comfort, you can live with relatively less phthalates by reading product labels and choosing only the phthalate-free options. You can even ask for phthalate-free medical devices when accepting blood donations or when undergoing kidney dialysis. However, living completely phthalate-free is essentially impossible in this day and age.
Dioxins are highly toxic persistent organic pollutants composed of carbon, oxygen, hydrogen, and chloride bonded in an extremely stable ring structure. It has been proven to cause developmental problems in humans, damage the immune system, and cause several types of cancers. Dioxins have also gained notoriety as one of the key components in the highly controversial Agent Orange defoliant. Due to its toxicity, dioxin production and use was banned by the Stockholm Convention in 2001.
Ambient dioxin levels in the environment have decreased sharply in the last three decades, owing in large part to a reduction in air emissions of dioxin from municipal and medical waste incinerators. PVC remains a culprit in contributing to overall dioxin levels. After all, incineration of PVC produced hydrochloric acid (HCl), a dioxin precursor. However, studies have shown that most of the dioxin in incinerated waste is formed due to the reaction of leftover chloride with ash particles in the presence of metal catalysts.
The results of the study indicate that dioxin production can be avoided by allowing all chlorine content in the PVC to be converted to hydrogen chloride. This can be done by ensuring complete incineration. Thus, avoiding dioxin is no longer a matter of WHAT is being burned but rather HOW it is burned. By implementing measures to maximize combustion efficiency, dioxin pollution can be avoided even when incinerating PVC.
3. Vinyl chloride monomer (VCM)
One of the major issues with PVC production is the fact that even its base monomer – vinyl chloride – is a proven carcinogen. People in the 1970s had to learn this the hard way, as workers in the polymerization section of BF Goodrich in Kentucky developed a very rare form of liver angiosarcoma. It is also a very volatile and flammable compound with a rather low flash point of only 78 °C. Upon burning, VCM can produce highly toxic hydrogen chloride gas and carbon monoxide.
Nowadays, most of the vinyl chloride produced is meant for the manufacture of PVC plastics. The most common method of producing VCM involves the reaction of chlorine and ethylene. Due to the toxicity of VCM, stringent regulations have been imposed regarding the removal of VCM from PVC products. Tests also have to be conducted on PVC products to ensure that they contain a minimum possible amount of unreacted VCM.
Lead has been widely used as an additive in PVC (and in other polymers) in the past several decades, as it has been proven to enhance the product’s heat stability, electrical resistance, and water absorption. However, lead has also been to cause nerve damage, kidney problems, infertility, cancer, and a host of other health problems. The biggest problem of using lead as an additive in PVC is the use of PVC pipes in potable water supply puts it into constant contact with chloramine, a chemical used for water treatment. This reaction results in leaching of lead from the PVC and into the water supply.
Recognizing the effects of lead on human health, PVC manufacturers in North America and Europe have voluntarily phased out the use of lead additives. Unfortunately, the rest of the world isn’t as self-regulating. If you are looking for PVC products, you should check for a “lead-free” label, as there is no current global standard on this matter.
5. Environmental concerns
Aside from concerns on their effect on human health, PVC has also been the subject of scrutiny due to its lasting effect on the environment. Upon disposal, PVC tends to degrade over time and develop microcracks. This eventually leads to PVC products getting reduced to plastic microparticles, which tend to soak up persistent organic pollutants around them. While sequestering pollutants can be beneficial to the environment, the problem is that these microparticles frequently in the habitat of animals, resulting in them getting ingested.
To be fair, this problem is not exclusive to PVC. Other common plastic products, such as HDPE, LDPE, and PP, can also break down into microparticles and produce the same effect. In fact, POP absorption has been shown to be magnitudes higher in HDPE and LDPE compared to PVC. Still, this shouldn’t be a matter of choosing between lesser evils, but instead should be about recognizing how our increasing of plastic products inevitably affects the environment that we live in.
Are there safer, more environment-friendly alternatives to PVC?
It’s very difficult, but not impossible, to live without PVC. With many people recognizing the potential problems of PVC, alternatives for common PVC applications are quite easily available. PVC bags and tubing for medical applications can be substituted by silicone or polyurethane. Nitrile and latex gloves have also been proven to be better alternatives to vinyl gloves.
PVC pipes, being very prevalent, are some of the most challenging to replace with non-PVC alternatives. Concrete is a common recommendation but can be very difficult to install. Stainless steel is a little simpler since they come pre-fabricated but is much more expensive. In any case, be careful when looking for metal piping alternatives, since some of then can come with an internal plastic coating that may have the same harmful effect as PVC.
Despite their best efforts in self-regulating, it is clear that PVC manufacturers are still fighting an uphill battle to prove the safety of PVC to humans and the environment. To be fair, it is worth noting that there has been no concrete evidence that PVC is hazardous to humans. Unfortunately, there has also been no strong evidence for the contrary.
In any case, it cannot be discounted that PVC is one of the most reliable and low-cost polymer products and has effectively revolutionized the industry of underground piping and, to a lesser degree, the medical and construction industries. However, like any other plastic, PVC is one material that we need to move past from eventually.