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Expandable graphite: A fire retardant additive for polyurethane coatings
Author(s) -
Duquesne Sophie,
Bras Michel Le,
Bourbigot Serge,
Delobel René,
Vezin Hervé,
Camino Giovanni,
Eling Berend,
Lindsay Chris,
Roels Toon
Publication year - 2003
Publication title -
fire and materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.482
H-Index - 58
eISSN - 1099-1018
pISSN - 0308-0501
DOI - 10.1002/fam.812
Subject(s) - intumescent , ammonium polyphosphate , polyurethane , fire retardant , graphite , materials science , char , coating , composite material , polymer , combustion , organic chemistry , chemistry
The study investigates the mechanism of fire retardancy induced by expandable graphite in a polyurethane coating. A complementary investigation to the spectroscopic study performed previously confirms that little interaction occurs between the matrix and the additive. X‐ray diffraction study demonstrates that the crystalline structure of the graphite is maintained during the intumescent process. The presence of free radicals in the protective shield is then demonstrated but at low concentration compared with classical intumescent systems, such as for example polyurethane/ammonium polyphosphate. Finally, the physical properties of the char are then investigated. Blowing measurement demonstrates the high degree of expansion of the layer which may partially explain the fire retardant performance of expandable graphite in polyurethane. Surface analyses by optical microscopy and optical profilometry also enable a better understanding of the efficiency of expandable graphite. In the absence of a fire retardant additive the coating displays cracks and holes, providing a pathway for oxygen diffusion as well as heat and mass transfer between the flame and the virgin polymer. Both phenomena are limited when expandable graphite is added to polyurethane. Consequently, fire retardancy of expandable graphite results more from a physical than from a chemical action. Copyright © 2003 John Wiley & Sons, Ltd.