PVC Plastics: Polyvinyl Chloride

Manufacture, Properties, Applications, and Environmental Concerns

Plastic pipes

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Polyvinyl chloride (PVC) is a popular thermoplastic that's odorless, solid, brittle, and generally white in color. It's currently ranked as the third most widely used plastic in the world (behind polyethylene and polypropylene). PVC is most commonly used in plumbing and drainage applications, although it's also sold in the form of pellets or as resin in its powder form.

Uses of PVC

The use of PVC is predominant in the home construction industry. It's regularly employed as a replacement or alternative for metal pipes (especially copper, galvanized steel, or cast iron), and in many applications where corrosion can compromise functionality and escalate maintenance costs. In addition to residential applications, PVC is also used routinely for municipal, industrial, military, and commercial projects.

In general, PVC is much easier to work with than metal pipe. It can be cut to the desired length with simple hand tools. Fittings and pipe conduits do not have to be welded. Pipes are connected with the use of joints, solvent cement, and special glues. Another advantage of PVC is that some products to which plasticizers have been added are softer and more flexible, as opposed to being rigid, making them easier to install. PVC is also widely used in both flexible and rigid forms as insulation for electrical components such as wire and cable.

In the healthcare industry, PVC can be found in the form of feeding tubes, blood bags, intravenous (IV) bags, parts of dialysis devices, and a host of other items. It should be noted that such applications are only possible when phthalates—chemicals that produce flexible grades of PVC and other plastics—are added to the PVC formulation.

Common consumer products such as raincoats, plastic bags, children's toys, credit cards, garden hoses, door and window frames, and shower curtains—to name just a few things you'll likely find in your own household—are also made from PVC in one form or another.

How PVC is Made

While plastics are certainly a manmade material, the two main ingredients that go into PVC—salt and oil—are organic. To make PVC, the first thing you have to do is separate ethylene, a natural gas derivative, from what's known as "the feedstock." In the chemical industry, petroleum is the feedstock of choice for numerous chemicals, including methane, propylene, and butane. (Natural feedstocks include algae, which is a common feedstock for hydrocarbon fuels, along with corn and sugarcane, which are both alternative feedstocks for ethanol.)

To isolate the ethanol, liquid petroleum is heated in a steam furnace and put under extreme pressure (a process called thermal cracking) to bring about changes in the molecular weight of the chemicals in the feedstock. By modifying its molecular weight, ethylene can be identified, separated, and harvested. Once that’s done, it’s cooled to its liquid state.

The next part of the process involves extracting the chlorine component from the salt in seawater. By passing a strong electrical current through a saltwater solution (electrolysis), an additional electron is added to the chlorine molecules, again, allowing them to be identified, separated, and extracted.

Now you have the main components.

When ethylene and chlorine meet, the chemical reaction they produce creates ethylene dichloride (EDC). The EDC undergoes a second thermal cracking process, which in turn, produces vinyl chloride monomer (VCM). Next, the VCM is passed through a catalyst-containing reactor, which causes the VCM molecules to link together (polymerization). When the VCM molecules link, you get PVC resin—the base for all vinyl compounds.

Custom rigid, flexible, or blended vinyl compounds are created by mixing the resin with different formulations of plasticizers, stabilizers, and modifiers to achieve desired properties that include everything from color, texture, and flexibility to durability in extreme weather and UV conditions.

Advantages of PVC

PVC is a low-cost material that's lightweight, malleable, and generally easy to handle and install. Compared to other types of polymers, its manufacturing process is not limited to the use of crude oil or natural gas. (Some argue that this makes PVC a "sustainable plastic" since it's not dependent on nonrenewable forms of energy.)

PVC is also durable and is not affected by corrosion or other forms of degradation, and as such, it can be stored for lengthy periods of time. Its formulation can be easily converted into different forms for use across a variety of industries and applications, which is a definite plus. PVC also possesses chemical stability, which is an important factor when PVC products are applied in environments with different types of chemicals. This characteristic guarantees that PVC maintains its properties without undergoing significant changes when chemicals are introduced. Other advantages include:

  • Biocompatibility
  • Clarity and transparency
  • Resistance to chemical stress cracking
  • Low thermal conductivity
  • Requires little to no maintenance

As a thermoplastic, PVC can be recycled and converted into new products for different industries, although due to the many different formulations used to manufacture PVC, it's not always an easy process.

Disadvantages of PVC

PVC can contain as much as 57% chlorine. Carbon—derived from petroleum products—is also often used in its manufacture. Due to the toxins that can potentially be released during manufacture, when exposed to fire, or as it decomposes in landfills, PVC has been dubbed by some medical researchers and environmentalists as the "poison plastic."

PVC-related health concerns are as yet to be statistically proven, however, these toxins have been linked to conditions that include but are not limited to cancer, fetal developmental setbacks, endocrine disruption, asthma, and diminished lung function. While manufacturers point to PVC's high salt content as being natural and relatively harmless, science suggests that sodium—along with the release of dioxin and phthalate—are in fact potential contributing factors to the environmental and health hazards PVC poses.

Future of PVC Plastics

Concerns regarding PVC-related risks and have prompted research into the use of sugarcane ethanol for feedstock rather than naphtha (a flammable oil obtained by the dry distillation of coal, shale, or petroleum). Additional studies are being conducted on bio-based plasticizers with the goal of creating phthalate-free alternatives. While these experiments are still in their initial stages, the hope is to develop more sustainable forms of PVC to lessen the potential negative impact on human health and the environment during the manufacture, use, and disposal stages.

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