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PVC, THE MATERIAL
PVC is one of the most common, widely used, and earliest plastics developed commercially.
It is formed using two natural resources, salt (57%) and oil (43%). Its use ranges from children's
toys to pipes, to window profiles, cables, and even to blood bags. It is estimated that the recent
world production is of the order of 56 billion pounds/year, of which U.S. production alone
accounts for 14.6 billion pounds, approximately 25%. Both national and international standards
are in place in most countries to control the production, qualities, and use of PVC. There is
practically very little hazard from the use of PVC. PVC has a solid history of more than 50 years
of commercial use. It was first developed in 1926 by Dr. Waldo Semon of BF Goodrich (Vinyl
Institute, 2003). The first commercial use was tried in shock absorber seals in the thirties, but the
rapid use of PVC did not develop well until the 1950s, with the rapid growth of irrigation piping
applications.
Most polymers contain carbon, hydrogen, and oxygen, all of which help combustion, and
thus, in general, polymers are susceptible to fire. However, PVC contains approximately 57%
chlorine by weight, which makes it flame retardant and therefore a preferred material in electrical
conduits and wiring insulation. Because of its minimal toxicity it is used in food wraps.
Moreover, additives used in PVC are closely regulated by the Environmental Protection Agency
(EPA), the Food and Drug Administration (FDA), and the Consumer Product Safety Commission
(CPSC) (Vinyl by Design, 2003).
Manufacture of PVC
Most structural engineers are familiar enough with the manufacturing and processing of steel,
and they are comfortable with its properties experienced through day-to-day structural
applications. Use of PVC for structural purposes may sometimes raise concerns because of the
unfamiliarity of the manufacture and processing of PVC. We will briefly discuss the fundamental
processes involved in PVC manufacture, and then discuss its general properties.
As said before, the manufacture of PVC involves two ingredients: petroleum and salt.
Petroleum or natural gas is put through a process, called cracking, to make ethylene, which is
combined with chlorine to produce ethylene chloride. Another cracking process transforms
ethylene chloride into the vinyl chloride monomer. Finally, through a process known as
polymerization, the monomer is converted into a fine, white PVC powder: vinyl resin. The
manufacturing schematic is given in Figure 1. Figure 2 shows the raw PVC resin powder (Vinyl
Institute, 2003).
The raw resin powder is then combined with other ingredients to achieve various desired
properties. The ingredients are called additives and modifiers. The proportions and the processes
used in combining these ingredients control the final properties of the PVC.
There are many additives used by the PVC industry. They include stabilizers, which prevent
decomposition of the PVC under heat; plasticizers, which reduce the melt velocity for processing;
PVC to develop better impact strength; fillers, which are basically inert materials that help to give
proper density and consistency; and colorants. Other useful additives include UV absorbers,
flame-retardants, antistatic agents, fungicides, odorants, and smoke control agents. There are
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