Novel C3N4/PANI@PA for enhancement of fire protection and smoke suppression in intumescent fire retardant epoxy coatings

Abstract Graphitic carbon nitride/polyaniline doped with phosphoric acid (g-C3N4/PANI@PA) hybrids was prepared by polymerising aniline monomer on the surface of g-C3N4 nanosheets, which used an in-situ chemical oxidative polymerisation method. Intumescent fire retardant (IFR) epoxy coatings with g-C3N4/PANI@PA were prepared, and fire resistance and waterproofing performance of coatings were investigated. The energy dispersive X-ray spectrometry image showed phosphorus element dispersing evenly on the fracture surface of epoxy composite with 0.25 wt% g-C3N4/PANI@PA (EP-0.25CP@PA), which indicated that g-C3N4/PANI@PA dispersed in coating evenly. The results of the cone calorimeter test (CCT) showed that the values of peak heat release rate (pHRR), total smoke release (TSR), total carbon monoxide production (TCOP) of pure epoxy resin (EP-0) were 1389.0 kW/m2, 22.6 m2 and 3.6 g, respectively. In addition, the related data of intumescent fire retardant coating (EP-IFR) were 374.8 kW/m2, 12.9 m2, and 2.1 g, respectively. When 0.25 wt% g-C3N4/PANI@PA was introduced into EP-IFR to get EP-IFR-0.25CP@PA sample, the pHRR, TSR, and TCOP values were reduced to 347.3 kW/m2, 7.9 m2, 1.5 g, which were reduced by 75.0%, 65.0%, and 60.0% compared with EP-0, respectively. Furthermore, g-C3N4/PANI@PA could also improve the hydrophobicity of IFR epoxy coatings. The water contact angle increased from 50.0° (EP-IFR) to 84.8° (EP-IFR-0.25CP@PA). It was confirmed that g-C3N4/PANI@PA could improve the fire protection, smoke suppression performance, and waterproof performance of IFR epoxy coating. All of those provide a certain theoretical support for applying g-C3N4/PANI@PA in intumescent fire retardant coatings.