Nano-ZnO modified geopolymer composite coatings for flame-retarding plywood

Herein the nano-ZnO/melamine polyphosphate (MPP) co-doped silica fume-based geopolymer composite coatings is fabricated for flame-retarding plywood. Its flame-retarding mechanism is investigated by microstructural characterizations and pyrolysis kinetics. The results show that an appropriate dosage of nano-ZnO (0.47 wt%) enhances flame retardancy, evidenced by the fire performance index increased to 2.98 s·m2·kW−1 from 1.10, the fire growth index (FGI) decreased from 0.48 to 0.23 kW·m−2·s−1, the flame retardant index (FRI) climbs from 1 to 2.79. Because the doped ZnO initiates the formation of ceramic-like Si/C/P residues, the as-formed ZnP4O11 is determined through the reactions between MPP and nano-ZnO. The ceramic-like reactions make the pyrolysis Eα rise from 204.30 to 255.61 kJ·mol−1 at 800 ∼ 1000 °C, according to the as-identified three-stage deceleration function (F3) of pyrolysis kinetics, resulting in the resilient and interpenetrating residues with a formaldehyde adsorption rate of 56%. It seeks effective recycling of metallurgical solid waste for preparing ecological flame-retarding coatings, proposing an efficient approach for quantitatively probing the Si/C/P residues.