Performance of different water-based resins in the formulation of intumescent coatings for passive fire protection

In civil construction, intumescent coatings are widely used in steel structures, because in a fire, this material loses approximately half of its elastic modulus at 500°C. The use of these paints is essential to ensure the structural safety of the construction as well as that of humans. The phenomenon of intumescence in paints occurs when they are subjected to high temperatures forming a carbonaceous layer that expands on the surface of the coating, with the main purpose of serving as a thermal insulator of the substrate. The development of paints with low impact on the environment has been stimulated due to restrictions on the emission of volatile organic compounds imposed by government agencies. Therefore, the development of water-based intumescent paints has become essential to meet these guidelines. In the present work, intumescent coatings were developed with different water-based resins: epoxy, acrylic and alkyd. The paints were formulated using expandable graphite as a blowing agent and expanded char source, ammonium polyphosphate as an acid source and lignin as a carbon source. The formulations were applied to steel substrates and exposed to burning tests to verify fire resistance, and in addition, the samples were characterized by combustion microcalorimetry, thermogravimetric analysis and pyrolysis coupled with gas chromatography and mass spectrometry. The carbonaceous layers were characterized by optical microscopy, scanning electron microscopy with dispersive energy spectroscopy, X-ray diffraction and Raman spectroscopy. The results of combustion microcalorimetry showed that the formulations containing lignin released less heat than the others. No toxic gases were detected in the pyrolysis of epoxy and acrylic system paints. The X-ray diffraction and Raman analyses proved the formation of thermally stable compounds in the carbonaceous layer.