Key Takeaways & Executive Findings
- •• Incorporation of modified fly ash geopolymer transforms phenolic foam from open-cell to closed-cell morphology, reducing pulverization ratio by 41% and enhancing mechanical properties by 15%. • The composite exhibits faster gelation dynamics and a significantly lower maximum reaction temperature (40 °C) compared to neat PF, mitigating spontaneous combustion risks. • PF/MFA composite demonstrates high reliability against gas leakage in laboratory coal mine plugging tests, indicating superior sealing performance. • Combustion of PF/MFA forms a silica hybrid char layer with higher graphitization degree and continuous closed-cell structure, effectively suppressing release of combustible volatiles and toxic gases.
Abstract
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.
1. Introduction
Coal spontaneous combustion, driven by oxygen infiltration in semi-open mined areas with fragmented coal and air leakage pathways, has caused catastrophic global incidents [1]. These events not only release toxic gases but also induce ecological degradation, including soil desertification and groundwater contamination [2]. Consequently, there is an urgent need to develop advanced filling and plugging materials to ensure the safety and ecological integrity of mining operations.
Phenolic foam (PF) has been widely used for building insulation and coal mine grouting areas, due to its low density, thermal conductivity, high flame retardancy, and corrosion resistance [3]. In underground coal mining, efficient sealing of high-gas zones and goaf areas is critical to prevent methane explosions and strata collapse [4]. PF has demonstrated exceptional value in high-gas zone filling and underground cavities plugging, particularly for its rapid curing and gas-barrier properties [5]. Despite these advantages, PF faces two critical limitations in practical implementation: (1) inherent brittleness leading to material pulverization during cyclic loading from roof convergence, and (2) excessive exothermic reactions during curing that elevate spontaneous combustion risks in coal-bearing environments [6]. These limitations not only compromise construction efficiency but also necessitate additional safety measures, thereby increasing operational cost.
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Yi Zhang, Xiaotian Nan, Sitong Zhang, Lan Jia, Fengbo Zhu, Wenwen Yu, Qiang Zheng (2025). Enhancing performance of mining phenolic filling materials by tailoring closed cell morphology with fly ash geopolymer. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.06.008
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Frequently Asked Questions
What is the main innovation of this research?
The research introduces a novel phenolic composite material filled with modified fly ash geopolymer, which transforms the foam structure from open-cell to closed-cell, significantly improving mechanical properties, reducing pulverization, and lowering reaction temperature for safer coal mining applications.
How does the incorporation of fly ash geopolymer affect the performance of phenolic foam?
Incorporation of modified fly ash geopolymer enhances interfacial bonding, leading to a closed-cell morphology. This results in a 41% reduction in pulverization ratio, a 15% increase in mechanical properties, faster gelation, and a lower maximum reaction temperature (40 °C), improving safety and reliability.
What are the environmental benefits of using fly ash geopolymer in phenolic foam?
Using fly ash, an industrial byproduct, reduces waste and promotes sustainable material development. Additionally, the composite's improved flame retardancy and reduced toxic gas release during combustion contribute to environmental protection.
How does the PF/MFA composite perform in coal mine plugging tests?
In laboratory-designed coal mine plugging tests, the PF/MFA composite demonstrated high reliability against gas leakage, indicating its effectiveness as a sealing material for high-gas zones and goaf areas.
What is the significance of the closed-cell morphology in the composite?
The closed-cell morphology enhances mechanical strength and reduces pulverization, while also improving gas barrier properties and flame retardancy by forming a continuous protective char layer during combustion.
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