Expandable Graphite

Expandable Graphite is a specialised intercalation compound produced by treating natural flake graphite with oxidising agents, typically a mixture of sulphuric acid and nitric acid, or sulphuric acid and hydrogen peroxide, under controlled conditions. The treatment intercalates sulphate or other species between the graphene layers of the graphite crystal structure, creating a staged intercalation compound that retains the layered structure of the parent graphite but contains reactive guest molecules between the layers.

When heated above the onset temperature, typically 150 to 220°C depending on the grade, the intercalated species decompose rapidly, generating gas that forces the graphene layers apart and causes the graphite to expand dramatically in the direction perpendicular to the basal plane. Expansion ratios of 150:1 to 300:1 are typical for commercial grades, producing a worm-like, low-density expanded graphite structure that acts as an effective thermal insulator and physical barrier to flame spread.

When incorporated into a polymer matrix or coating, the expansion of the graphite particles upon heating creates a thick, coherent char layer, known as an intumescent char, that insulates the underlying substrate from heat and prevents the spread of flame. The char is mechanically stable and resistant to collapse, maintaining its insulating function throughout a fire event.

Expandable Graphite is available in grades differentiated by particle size, expansion ratio, and onset temperature. Coarser grades typically exhibit higher expansion ratios; finer grades provide better dispersion in polymer matrices. ROCC Global sources Expandable Graphite from established producers in Asia Pacific and Europe, with expansion ratio verification and particle size analysis provided for each consignment.

Expandable Graphite is used as an intumescent flame retardant additive across passive fire protection applications. In firestop systems, including intumescent strips, collars, and pillows used to seal penetrations in fire-rated walls and floors, it is the primary active ingredient, expanding on exposure to heat to seal the penetration and prevent the passage of fire and hot gases. In intumescent coatings applied to structural steelwork, it contributes to the formation of a thick, insulating char layer that delays the heating of the steel section and extends the time to structural failure in a fire. In flexible polyurethane and polyethylene foams used in construction sealing applications, it provides intumescent fire performance that causes the foam to expand and seal gaps upon exposure to heat. In rigid polymer compounds and engineering plastics, it is used in combination with other flame retardants to achieve the required fire performance classification under standards such as UL 94 and EN 13501.