Enhancing performance of mining phenolic filling materials by tailoring closed cell morphology with fly ash geopolymer

Phenolic foam (PF) has attracted growing attention in plugging areas due to its lightweight, flame retardancy and high fillability, yet its friable character and high reaction temperature severely weaken its potentials toward practical coal mining applications. Herein, a novel phenolic composite material filled with modified fly ash (MFA) geopolymer has been proposed to address the above issues. By modifying fly ash (FA) particles with siloxanes, robust interfacial bonding between the organic PF polymer and inorganic geopolymer network has been established, which enables modulation of their micro-morphologies to optimize their macro performances. The foam structure of PF evolves from an open-cell to a closed-cell morphology with the incorporation of MFA, leading to a decreased pulverization ratio (41%) while enhanced mechanical properties (15%). Compared with neat PF, the composite exhibits faster gelation dynamics during curing, with a maximum reaction temperature as low as only 40 °C. PF/MFA composite show high reliability against gas leakage during a laboratory designed coal mine plugging test. Furthermore, the formation of a silica hybrid char layer with higher graphitization degree and a multiple continuous closed-cell structure following the combustion of PF/MFA effectively inhibits the release of combustible volatiles and toxic gases. It is provided that this strategy of geopolymer filled polymer cross-linking networks with tunable morphology opens up an avenue for advanced mining phenolic filling materials.