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Expandable Graphite

Expandable graphite is manufactured from flake graphite by treatment with strong acids like sulphuric or nitric acid. The acid is trapped in the crystal layers of the graphite ("intercalated"). When it is heated, the graphite starts to expand up to several hundred cm3 per gram, forming a protective layer for the polymer. Expandable graphite is used in plastics, rubbers (elastomers), coatings, textiles and especially in polymeric foams. To achieve an optimum flame retarding effect, the use of synergists like ammonium polyphosphate or zinc borate is often necessary. The black colour of graphite limits its applicability in some cases.