Intumescent systems basics

The effectiveness of intumescent flame retardants is frequently reduced when fillers are added. Interactions can be either chemical or physical. Materials which are basic in character such as aluminium and magnesium hydroxides and calcium carbonate tend to interfere chemically with the phosphoric acid precursor in the intumescent system, presumably forming inorganic phosphates. Such antagonistic behaviour can be easily recognized by an almost complete lack of char formation. 

It has also been diseovered that potassium earbonate enhances the charring of polymers containing pentaerythritol-silica combinations as flame retardants. This has led to the discovery of base-catalysed intumescence of potassium bitartrate. Combinations of potassium bitaitrate and pentaerythritol show improved intumescence but carbon char oxidation by glowing combustion has remained a problem. Base catalysis is an attractive alternative to conventional acid-catalysed intumescent flame retardant systems as it could help to alleviate corrosion problems during polymer processing. Unfortunately, strongly basic residues also catalyse the oxidative destruction of the char-foam at high temperatures. 

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