Sodium lignosulfonate improves the compatibility of melamine polyphosphate with graphite-containing alkali-activated cenospheres-based coating for flame-retarding plywood

Abstract

Cenospheres, a common industrial solid waste generated by coal-fired power plants, have become a significant environmental concern due to their emissions. This has created a need for practical solutions. In response, a novel organic-inorganic hybrid coating, the melamine polyphosphate@sodium lignosulfonate@graphite-containing alkali-activated cenospheres-based coating (MPP@LS@FG-ACC) has been synthesized using the sol-gel method for flame-retarding plywood. The research demonstrates that an appropriate LS (1.00 wt%) pretreated MPP improves its compatibility with the inorganic siliceous coating, enables more phosphorus-containing groups within MPP to participate in the as-formed Si-P-C flame retardant, which transforms into interpenetrating, robust, and nonflammable resilient residues during burning. Consequently, the flame retardancy is enhanced, as evidenced by a reduction in the peak heat release rate (from 98.65 to 63.73 kW·m−2), an increase in the flame retardancy index (from 1 to 2.58), and a decrease in smoke production by approximately 49 %. Additionally, the Z.-L.-T. Three-dimensional diffusion-reaction model governs the composite coatings' pyrolysis. Kinetics calculations clarify that an appropriate LS makes its Eα rise from 94.13 to 122.89 kJ·mol−1 at 970–771 ℃, corresponding to enhanced thermal stability for blocking heat and fire. Hence, this research presents an effective strategy for enhancing the compatibility of MPP by LS pretreatment and proposes an efficient approach for reusing cenospheres, improving the flame retardancy of cenospheres-derived building materials.