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A review of recent developments in the applications and actions of intumescent ®re-retardance is given. An attempt has been made to classify the main systems of importance such as melamine, ammonium polyphosphate, melamine phosphate, pentaerythritol phosphate, sodium silicate, vermiculite, expandable graphite and microbeads. They are de®ned in terms of the Berthelot number which is the product of heat of vaporization or decomposition and volume of gases evolved. In principle, only two kinds of gases are produced from this group, namely water vapour and ammonia (from melamine). The heats of decomposition are readily calculated from heats of formation. An important aspect which is not included in the Berthelot number is the ignition residue in the shape of glassy foam or a cellular enamel. # 2000 Society of Chemical Industry Keywords: intumescent;¯ame retardant; plastic; vermicular graphite; sodium silicate; intumescent paint; thermal insulation INTRODUCTIONThe term intumescence derives from medicine and means swelling under in¯ammation. Intumescent compounds and formulations are those which expand in the case of ®re under the in¯uence of heat. The number of intumescent compounds and formulations available is still much larger than cases of commercial applications. In recent developments intumescent agents for paints 1,2 are not only used as coatings but are also incorporated directly into plastic materials. Flame-retarded polyole®nes 3 and polyamides 4 are produced by this technology, for example melamine phosphates are added to glass-reinforced polyamides to meet a V-0 classi®cation in the UL 94 test, UL 94 is one of the most important UL standards relating to ®re safety test methods and requirements and contains several ®re tests for plastics.

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The combustion kinetics of a laminate with intumescent behavior were determined by thermogravimetry for heating rates between 5 and 20 K/min and a final temperature of 873 K. The devolatilization stage consists of three consecutive first-order reactions that can be associated with the release of (1) water vapor (from aluminum trihydrate), ( 2) HCl (from polychloroprene), and (3) a gaseous mixture (from expansible graphite), followed by charring. The corresponding activation energies are 114, 140, and 83 kJ/mol. The second stage is the heterogeneous combustion of the active part of the intumescent char. This process is described by a one-step reaction whose rate presents a power-law dependence (n ) 1.98) on the solid conversion and an activation energy of 182 kJ/mol. The thermal response of a composite system that uses the intumescent material as a coating for thin steel slabs was also investigated. For external temperatures of 625-1025 K, the sequential chemico-physical changes undergone by the intumescent coating highly affect the dynamics of steel heating.

Under the influence of heat intumescent paints with stoichiometric compositions decomposed to defined compounds: Ammonium polyphosphate degraded to polyphosphoric acid and ammonia. Polyphosphoric acid reacted with pentaerythritols and glycerol to cyclic phosphoric acid esters, which were identified as the blowing agents. Melamine and polyphosphoric acid combined to melamine polyphosphate and dipolyphosphate. In further degradation of polyphosphoric acid, it dehydrated to phosphorus pentoxide, which reacted with titanium dioxide further to titanium pyrophosphate. Intumescent paints with higher efficiency could be developed by the addition of glycerol, which reacted to phosphoric esters with lower temperatures of decomposition.