Effect of Modified Halloysite/Expandable Graphite Addition on Thermal and Intumescent Properties of the Fire-Resistant Paints for Steel

Abstract The article presents results of the research on the influence of halloysite and its modified versions in a configuration with expandable graphite on thermal stability, integrity and intumescence of the fire-resistant paints for steel based on the epoxy resin and ammonium polyphosphate/pentaerythritol/melamine (APP/PER/MEL) system. The preliminary scanning electron microscope (SEM) analysis showed that halloysite modified with sulfuric acid (M2) has the best surface expansion. Nanotubes increased their volume and nanoplates were more delaminated. Temperature tests of the fire-resistant paints and subsequent SEM analysis confirmed these results, as a homogeneous structure with 50-fold multiplication was obtained for the sample with modified halloysite M2/expandable graphite, while the sample with pure halloysite/expandable graphite multiplied only 15-fold. Thermogravimetry/ differential scanning calorimetry (TG/DSC) analysis showed that the modified halloysite can significantly change the course of thermograms, even at low addition (7 wt%), and the mass loss can be reduced by up to about 13 wt%. The obtained results showed that the modified halloysite can successfully cooperate with expandable graphite and can be introduced into the intumescent system without deteriorating the physicochemical properties of the coating.