Expandable Graphite Flame Retardant (Intumescent Graphite)

Expandable Graphite (EG) is an intercalation compound of graphite in which sulfuric acid or acetic acid molecules are inserted between graphite layer planes. On exposure to fire or heat (typically above 150–200°C), the intercalated acid vaporizes and causes the graphite layers to expand rapidly — up to 300–500 times the original volume — creating a worm-like expanded graphite structure. This expansion generates a thick, insulating, and cohesive char layer that acts as a physical barrier between the flame and the substrate, dramatically reducing heat transfer and combustible gas generation.

Expandable graphite is a highly effective halogen-free flame retardant for rigid and flexible polyurethane (PU) foam systems, producing the lowest smoke density and smoke toxicity among practical FR approaches for PU foam. In rigid PU insulation foam for construction (PIR/PUR panels), EG at 3–8 phr provides EN 13501-1 Class B or Class B-s2 fire performance. It is also used in flexible PU foam for furniture and in PU sealants and adhesives for construction joints requiring fire resistance ratings under EN 1366 or ASTM E814.

In unsaturated polyester and epoxy resin systems, expandable graphite can be combined with APP and melamine for synergistic intumescent performance. EG provides the physical char expansion and barrier effect, while APP provides the acid for esterification. In pultruded UPR profiles and sandwich panels, EG at 10–20 phr combined with ATH or APP achieves Class B1 or Class 1 fire performance ratings for construction products.