Performance of phosphorylated tannin-based intumescent coatings in passive fire protection

The aim of this study was to evaluate the performance of intumescent coatings based on chemically modified tannin in passive fire protection. For this purpose, chemical modification of tannins was carried out with phosphorus pentoxide or phytic acid. Following this, a set of paints were formulated, each of which contained one of the tannins in combination with expandable graphite and ammonium polyphosphate as pigments. The chemical modification of the tannins was evidenced by Fourier transform infrared spectroscopy analysis, and the thermal protection of mild steel samples coated with the prepared organic coatings was evaluated after the exposure of samples to a Bunsen torch. During the tests, temperature data and thermographic images of the steel surface were collected. The coatings and the chemically modified tannins were also evaluated using thermogravimetric analysis and microscale combustion calorimetry. It was found that all coatings provided good fire protection, and the temperature of the steel substrate after 30 min of the experiment did not exceed 130°C in the formulations where only the chemically modified tannin with the expandable graphite was used.