Tuesday, 1 April 2014

Itac use chlorine as a compound

Elizabeth Henderson
Product Development Manager
This month’s blog discusses an element used by Itac only as a compound – chlorine. Every day we all encounter sodium chloride as crystalline table salt, scattered on crisps and peanuts. Salt played a major role in the development of the science of crystallography, as its structure was the first to be determined by the scattering of X-rays. Understanding of the chemistry of the Earth’s atmosphere has increased dramatically during recent decades and many chlorine compounds formerly used in industrial applications have been identified as causes of harm to the ozone layer and upper atmosphere. But the unique properties of chlorine mean it still plays a role in our specialised materials – we use modern control methods to minimise escapes of volatile chemicals and whenever possible we replace chlorine compounds with less harmful products.
Gaseous chlorine readily forms chlorine radicals in the presence of UV light, and this very reactive species plays a major part in the flame retardant products we make at Itac. In a fire there’s very little UV light and gaseous chlorine is hard to use efficiently, so we use chlorine-containing polymers to deliver chlorine radicals into the flames. The polymers contain carbon-chlorine bonds which are broken to release the radicals into the fire gases. These gases are a mixture containing hydrocarbons which react with the chlorine radicals to form hydrogen chloride gas. This key species reacts with hydroxyl radicals also in the fire gases to give water and regenerate the chlorine radical. The water is a stable material so hydroxyl radicals cease to be active, and the chlorine radicals are regenerated to carry on working.
At Itac most of the flame retardant coatings we produce are for textile applications, and we introduce the chlorine compounds used along with other flame retardant technologies, either by using a chlorinated polymer (eg Neoprene) for the binder system or by incorporating a halogenated oil into a more conventional polymer mix. Use of a conventional hydrocarbon means a plentiful supply of fire gases to react with the chlorine radicals. The fibre used for the textile has a powerful effect on the combustion behaviour, and the classification of the fire performance of the finished textile depends on both the fabric and the coating.

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