A comparative analysis of microstructure, water retention, thermal stability and fire performance between gel and film-forming fluoroprotein firefighting foams

• Synthesis of an environmentally friendly gel foam using guar gum and borax and surfactant composite. • Determination of optimal gel foam formulations with enhanced thermal stability based on orthogonal analysis of foamability. • Better water retention capacity and thermal stability of the gel foam compared to a commercial FFFP firefighting foam. • Investigation of gelling mechanisms, synergistic effects of foaming components and the formation of a 3D network structure. • Evaluation of fire suppression and anti-burnback performance in large pool fire tests against the FFFP. Firefighting foams are commonly used for suppressing and extinguishing large-scale liquid fuel fires. However, traditional foams such as aqueous film-forming foams (AFFFs) and film-forming fluoroprotein foams (FFFPs) have some known limitations including worsened thermal stability under strong radiation and difficulty in biodegradation due to the presence of perfluorooctyl sulfonate. In this study, a new gel foam was developed using bio-based guar gum (GG) and borax (B), in combination with a composite foaming agent of C8-14 alkyl glucoside (APG-0814) and alkyl ethoxy polyglycosides (AEG). The best performed gel formulations were selected based on orthogonal analysis of formability and stability. Subsequently, their microstructure, water retention capacity and thermal stability were evaluated against a commercial FFFP. Finally, fire extinguishing and burnback tests using the gel foams were conducted. Results showed that the formulation with 0.5 wt% composite foaming agent, 0.4 wt% GG and 0.005 wt% B has the overall best performance. Its water retention rate is 56.9 % after 60 min compared to 47.8 % for the FFFP. Whilst its extinguishing time was similar to that of the FFFP, its 90 % burnback time shows a 152.7 % increase compared to the FFFP. The improved anti-burnback performance can be attributed to the stable gel foam skeleton which enhanced both water retention capacity and thermal stability. This research provides not only a holistic approach for assessing fire performance of existing firefighting foams but a basis for further development of firefighting gel foams.