A thermally stable sodium alginate-based gel foam with intumescent performance for inhibiting coal spontaneous combustion

Fires caused by spontaneous coal combustion pose a serious threat to mine safety. Although sodium alginate-based gel foams have made significant progress in preventing and controlling coal spontaneous combustion, they still suffer from the limitation of being prone to rupture and collapse under high temperatures. Biomass intumescent flame retardants not only have excellent thermal protection performance at high temperatures but also have good compatibility with sodium alginate. Therefore, this study constructed a biomass intumescent flame retardant (PLSL) and incorporated it into a sodium alginate-based gel foam system (TRGF) to prepare an intumescent thermally stable gel foam (PLSL-TRGF). The results indicated that there are hydrogen bonds and electrostatic interactions between PLSL and TRGF. PLSL-TRGF could form an insulating intumescent char layer and deliver excellent fire suppression performance while inhibiting coal spontaneous combustion. In addition, PLSL-TRGF effectively reduced the influence of heat and delayed the temperature rise, with the temperature reduction rate up to 89.30%. At 200℃, the CO inhibition rate of coal treated with PLSL-TRGF increased to 77.41%, and the Cross Point Temperature increased by 8℃ compared with that of treated with TRGF, showing excellent coal spontaneous combustion inhibition performance. Meanwhile, the fire extinguishing efficiency of PLSL-TRGF increased by 83.51% compared with that of TRGF. PLSL‑TRGF mainly works through cooling, oxygen isolation and coverage, free radical capturing, and forming an intumescent char layer at high temperatures to further block the transfer of heat and oxygen. This study provides a novel strategy for the development of high performance gel foams and promotes the advancement of coal spontaneous combustion prevention and control technology.