Objective In order to improve the flame retardant properties of wood, and extend the application of bio-based flame retardant materials in wood, we prepared expandable composite flame retardant coatings using all-bio-based materials (chitosan/gelatin/phytic acid), and explored the properties in the wood application.

Method The composite intumescent flame-retardant coating (CGPx) was prepared by chitosan/gelatin as the film-forming substance and water as the solvent, and was prepared according to the mass ratio of chitosan, gelatin, phytic acid of 3∶2∶(0−1.5). The flame-retardant coating layer of wood was prepared by coating it on the wood surface. Scanning electron microscopy and Fourier transform infrared spectroscopy were used to analyze the morphology and elemental distribution of the coating layer. A pencil hardness tester and an adhesion test were used to evaluate the hardness and adhesion of the coating layer. Scanning electron microscopy, thermogravimetric test, combustible fire test, and cone calorimetry test were used to comprehensively evaluate the thermal stability, flame retardancy of the treated wood. Finally, scanning electron microscopy and Fourier transform infrared spectroscopy were used to analyze the morphology and elemental distribution of the residual charcoal and to analyze the flame retardant mechanism.

Result CGPx showed excellent adhesion and hardness on wood, with the CGP1.5 group achieving an adhesion rating of Class 1 and a pencil hardness of 7H. CGPx wood showed excellent thermal stability, with the CGP1.5 group achieving a residual charcoal rate of 44.2%. CGPx wood showed excellent flame resistance in fire and combustion tests. In the cone calorimetry test, the peak heat release rate of the CGP1.5 group was reduced by 34.3%, the time of the peak rate was delayed to 284 s, the total heat release was reduced by 15.5%, the CO and CO₂ release rates were also reduced, the fire index was 0.189 and the flame growth index was 0.708. The flame retardancy of the treated wood was enhanced.

Conclusion The treatment coated wood with all-biobased flame-retardant coatings, can effectively improve the thermal stability and flame-retardant properties of wood, and enrich the green and sustainable flame retardant system of wood.