Polyvinyl Chloride (PVC) is a thermoplastic material that is used in a myriad of products including water pipe and electrical conduit. It is a polymer whose long chain molecules are made from the building blocks of vinyl chloride. Additives are used to enhance the properties of PVC for specific applications. Finished products come in a number of colours, are tolerant to ultraviolet light, and have various degrees of flexibility.
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The two raw materials used in the manufacture of PVC are seawater and oil. Salt derived from seawater is used to make chlorine gas and petroleum oil is the original source for ethylene gas. Chlorine and ethylene are the two main ingredients needed to make PVC.
Chlorine is produced from a saline solution by the process of electrolysis. A solution of sodium chlorine, or common table salt, is placed in a container with electrodes. When electric current is applied, the positive electrode attracts chloride ions in the solution where they combine to form chlorine gas.
Ethylene is a colourless and odourless gas with the chemical formula C2H4. It is highly flammable and can cause explosions if mishandled. It is produced commercially from the refining of petroleum.
The chlorine and ethylene gases are combined to produce ethylene dichloride which is converted at high temperatures to vinyl chloride (CH2=CHCl). The vinyl chloride molecules are then polymerised to form the PVC resin. Other compounds are added to improve its appearance and physical and chemical properties. The finished product is formed into pipe or other products where it hardens as it cools.
A number of compounds can be added to raw PVC. The most common additives are pigments to add colour, UV inhibitors to protect the material from being degraded by prolonged exposure to sunlight, and plasticisers to adjust the degree of flexibility of the specific product. Most plasticisers come from a chemical group called phthalates.
Toxicity of Materials
Chlorine in the gaseous form is dangerous because it is a severe irritant to the skin, eyes, and respiratory system. Ethylene chloride compounds that are made in the manufacturing process and not converted into polymers are known to be carcinogenic. There are remnants of these compounds that are not combined in the finished PVC which makes water pipe and other products potentially hazardous as well. The phthalates that are used as to increase plasticity are also very toxic.
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