|MadSci Network: Chemistry|
Pyrolysis (heating till smoke evolves) of PVC causes the production of char and tar and the formation of chlorinated hydrocarbons, mainly chlorobenzene. Incineration of PVC leads to the formation of chlorinated dibenzodioxines and dibenzofuranes in the flue gas. Thermal degradation of PVC in an inert atmosphere produces HCl-gas, gaseous and liquid hydrocarbons, char and an inorganic solid residue, originating from additives. In a steam atmosphere at high temperatures the char fraction will not accumulate, like in pyrolysis, but will be converted to carbonmonoxide and hydrogen. The inorganic solids will be separated from the product gas, HCl can be recovered and the high caloric hydrocarbon residue can be used for energy recovery. By virtue of its chlorine content, PVC has inherent flame retardant properties, and it is therefore unlikely that a spark from a welder's torch could ignite PVC cables for example. An interesting fact with regard to PVC products is the deterioration of old toys made of PVC such as Barbie dolls. Old Barbie dolls sometimes develop green patches on their skin. The culprit is not PVC but plasticizers added to it to make it flexible. An interesting article can be found at http://www.natmus.dk/cons/lab/barbie/bb.htm. In summary melting and subsequent evolution of smoke does result in toxic products being evolved. IF you need info on the toxicity of the chemicals I had listed above you can look up what are called MSDS sheets on the web. MSDS stands for Materials Safety Data Sheets. Goto www.google.com and type “MSDS Sheets” in the search box. Hope this helps.
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