Influence of expandable graphite on fire resistance and water resistance of flame-retardant coatings

Expandable graphite (EG) coating and ammonium polyphosphate–pentaerythritol–melamine (APP–PER–MEL) coating were prepared. Thermal degradation and char formation of the coatings were investigated by differential thermal analysis (DTA), thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results have shown that the anti-oxidation and fire-resistant properties of expandable graphite coating containing EG with size of 74 μm are better than those of APP–PER–MEL coating. The static immersion test was applied to study water resistance of the coatings, and the fire protection test and mechanical test were used to analyse heat insulation and mechanical properties of coatings before and after water immersion. The fire-resistant and mechanical properties of APP–PER–MEL coating were severely damaged by water immersion, whereas EG coating containing 8.5% EG with size of 74 μm could retain the good fire resistance even after 500 h water immersion.