Evaluation of the expandable graphite/polyaniline combination in intumescent coatings

In this study, the addition of expandable graphite to paints containing polyaniline (PAN') and ammonium polyphosphate (APP) as pigments was investigated in order to improve the fire protection performance of the intumescent coatings. The corrosion protection on application to mild steel was also evaluated, since PANI is often applied as an anticorrosion agent in organic coatings. The thermal protection of mild steel samples coated with organic coatings containing PANI-ES (emeraldine salt) or PANI-ES/APP, APP and expandable graphite in the formulation was evaluated after sample exposure to a Bunsen torch for 30 min. During the test, thermography images and temperature data for the steel surface were collected. The coatings were also evaluated by thermogravimetric analysis (TGA) and microscale combustion calorimetry (MCC). The corrosion behaviour of samples coated with organic coatings was investigated through electrochemical impedance spectroscopy (EIS) measurements taken in a 3.5% NaCl solution. It was found that all coatings provided good fire protection, and the steel substrate temperature after 30 min of experiment did not exceed 200 degrees C. However, only the coating containing 5% PANI-ES/APP in the formulation showed good protection against corrosion. This behaviour can be attributed to the high porosity of the coatings.