What is Polyvinyl Chloride (PVC), and What is it Used For?
Polyvinyl Chloride (PVC) is one of the most commonly used thermoplastic polymers in the world (next to only a few more widely used plastics like PET and PP). It is a naturally white and very brittle (prior to the additions of plasticizers) plastic. PVC has been around longer than most plastics having been first synthesized in 1872 and commercially produced by B.F. Goodrich Company in the 1920s. By comparison, many other common plastics were first synthesized and became commercially viable only in the the 1940s and 1950s. It is used most commonly in the construction industry but is also used for signs, healthcare applications, and as a fiber for clothing.
PVC is produced in two general forms, first as a rigid or unplasticized polymer (RPVC or uPVC), and second as a flexible plastic. Flexible, plasticized or regular PVC is softer and more amenable to bending than uPVC due to the addition of plasticizers like phthalates (e.g. diisononyl phthalate or DINP). Flexible PVC is commonly used in construction as insulation on electrical wires or in flooring for homes, hospitals, schools, and other areas where a sterile environment is a priority, and in some cases as a replacement for rubber. Rigid PVC is also used in construction as pipe for plumbing and for siding which is commonly referred to by the term “vinyl” in the United States. PVC pipe is often referred to by its “schedule” (e.g. Schedule 40 or Schedule 80). Major differences between the schedules include things like wall thickness, pressure rating, and color.
Some of PVC plastic’s most important characteristics include its relatively low price, its resistance to environmental degradation (as well as to chemicals and alkalies), high hardness, and outstanding tensile strength for a plastic in the case of rigid PVC. It is widely available, commonly used and easily recyclable (categorized by resin identification code “3”).
What are the Characteristics of Polyvinyl Chloride (PVC)?
Some of the most significant properties of Polyvinyl Chloride (PVC) are:
Density: PVC is very dense compared to most plastics (specific gravity around 1.4)
Economics: PVC is readily available and cheap.
Hardness: Rigid PVC is very hard.
Strength: Rigid PVC has extremely good tensile strength.
Polyvinyl Chloride is a “thermoplastic” (as opposed to “thermoset”) material which has to do with the way the plastic responds to heat. Thermoplastic materials become liquid at their melting point (a range for PVC between the very low 100 degrees Celsius and higher values like 260 degrees Celsius depending on the additives). A major useful attribute about thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Instead of burning, thermoplastics like polypropylene liquefy, which allows them to be easily injection molded and then subsequently recycled. By contrast, thermoset plastics can only be heated once (typically during the injection molding process). The first heating causes thermoset materials to set (similar to a 2-part epoxy) resulting in a chemical change that cannot be reversed. If you tried to heat a thermoset plastic to a high temperature a second time it would simply burn. This characteristic makes thermoset materials poor candidates for recycling.
Why is Polyvinyl Chloride (PVC) used so often?
Rigid PVC in particular has very high density for a plastic making it extremely hard and generally very strong. It is also readily available and very economical which combined with the long-lasting characteristics of most plastics make it an easy choice for many industrial applications like construction.
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