Polyvinyl chloride refers to the polymer that is third-most manufactured polymer. It is produced following a polymerization process using the vinyl chloride as the monomer (Patrick). The polyvinyl chloride is abbreviated as PVC and was accidentally produced Eugen Baumann, a chemist in France in the year 1835 and again in 1872 by Ivan Ostromislensky and his colleague Fritz Klatte. During the two incidents, the vinyl chloride was exposed to sunlight resulting in the production of a white solid in the flask where vinyl chloride was contained. Some of the major uses of PVC include in the construction since its more effective compared to the other materials that were traditionally used such as ironwood or copper in profile and pipe application. It is also useful in plumbing, inflammable products and insulation of electrical cable among other uses (Greenpeace).
Procedures that are employed in the production of PVC include emulsion, suspension and bulk polymerization. Using the suspension polymerization, the particles that are formed have a mean diameter of up to 180μm while using the emulsion polymerization the diameter of the particles formed may be as low as 0.2μm. During the production of the polymers, both the vinyl chloride monomer and water are added into the reactor followed by the initiation of the polymerization process by a polymerization initiator. In addition, other additives are added. Once the process has started, the content in the chamber is mixed continuously just to ensure that uniform particles are formed and at the same time maintaining the suspension. Cooling is necessary during the reaction since the polymerization process is an exothermic reaction. Addition of water during the process is also necessary to maintain the suspension as water is being wasted during the process (Patrick).
For the polymerization initiators to start the vinyl chloride monomer polymerization, they first break down first starting off a radical chain reaction. Some of the polymerization initiators include dicetyl peroxydicarbonate, and dioctanoyl peroxide. These two initiators have the fragile O-O bonds that are used to form radicals. Some initiators have the capability of starting the reaction in a rapid manner and decay very fast while others initiate the reaction slowly but able to stay for a longer time. Different initiators are usually combined in order to provide a uniformed rate of polymer formation. Once the product has attained structures that are 10 times the weight of the monomer, the polymer starts to precipitate while the polymerization process progresses to in the vinyl chloride monomer droplets (Patrick).
Once the polymerization process is complete, the produced PVC is taken through a degassing process and then stripped to eliminate any excess vinyl chloride monomer. The polymer is then taken through a centrifugation process in order to eliminate water and the product is then dried using hot air. The resulting powder is then sieved and stored or pelletized. The size of the particles produced usually depends on the kind of polymerization and the products produced have varying applications depending on the produced PVC (Patrick).
The end product from polymerization is usually a PVC product that is not modified and one that has no specific function. Before using PVC in the production of other products, it requires conversion into a different compound through the addition of additives like the UV-stabilizers, lubricants, heat-stabilizers, processing aids, lubricants, fillers, biocides, smoke suppressors, as well as the thermal modifiers. The kind of additive that is used is usually dependent on the specific use of the material being processed (Patrick).
One of the additives that are added almost in all the vinyl products is the phthalate plasticizers and works to improve the performance characteristic of the vinyl products. The phthalate plasticizers are selected based on their low cost, volatility and compatibility with the vinyl polymers. The heat stabilizers are also added to the PVC products. Addition of heat stabilizers reduces the chances of losing the HCL as the dehydration process begins at a temperature above 70 °C. Some of the heat stabilizers that are used include heavy metal derivatives and the metallic soaps or the metal soaps from fatty acids such as the calcium stearate. The quantity of the additive added varies and may range from 2% to 4%, and the best choice is made depending on the final product application, regulatory authorization, technology available for processing, performance specification, and the cost (Patrick).
Some of the physical properties of the PVC include a density of 1.1-1.45g/cm3, thermal conductivity of 0.14-0.28 W/(m.K), flexibility strength of 10500psi, and resistivity of 1012–1016 depending on the PVC flexibility. The PVC materials have very high mechanical properties. These properties increase as the molecular weight of the product increase but reduce as the temperatures go high. They, however, have poor heat stability at temperatures above 140 °C. At such temperatures, the PVC begins to decompose as its melting point is 160 °C. They offer good electricity insulation properties although due to their increased polar nature they have less isolative properties compared to the non-polar polymers like the polyethylene (Patrick).
Works Cited
Greenpeace. Polyvinyl Chloride. 2013. Online. 1 April 2014. <http://www.greenpeace.org/international/en/campaigns/toxics/polyvinyl-chloride/>.
Patrick, Stuart. Practical Guide to Polyvinyl Chloride. Shawbury: iSmithers Rapra Publishing, 2005. Print.
