Recycling cenospheres to construct chitosan bonded-ammonium polyphosphate/dipentaerythritol hybrid geopolymer coatings for flame-retarding plywood

Cenosphere is an industrial solid waste produced by coal-fired power plants. Its large discharge has resulted in significant environmental problems, and how to solve this problem has become a top priority. In this research, chitosan (CS) bonded-ammonium polyphosphate (APP)/dipentaerythritol (DPER) are employed to construct cenospheres-based geopolymer coatings using the sol-gel method for flame-retarding plywood. The experimental results indicate that an appropriate pretreatment of APP with CS (0.40 wt.%) facilitates the formation of geopolymer coatings, resulting in non-combustible resilient residues during combustion, its effectively block heat and fire sources, significantly decreasing the peak heat release rate from 108.89 to 90.61 kW·m-2 and reducing about 80 % of smoke production. Meanwhile, the three-level chemical reaction model is identified to govern the hybrid coatings' pyrolysis. The calculations clarify that an appropriate CS increases its Eα from 266.03 to 345.16 kJ·mol-1 at 727 ∼ 1000 °C, corresponding to enhanced thermal stability. Furthermore, the yielded residues exhibit a formaldehyde adsorption rate of 71.6%, attributed to the formation of interpenetrating networks. Incorporating CS-pretreated APP in cenospheres-based coatings for designing Si-C-P hybrid coatings provides an effective method for recycling cenospheres and promotes the development of sustainable building materials.