📄 chemistry

Experimental study on foam drainage of AFFF: Additive regulation, thermal transition, and fire-extinguishing verification

This study investigates the synergistic effects of additives and the dual regulatory mechanism of temperature on AFFF foam drainage kinetics to establish a quantitative relationship with fire-extinguishing performance, ultimately enabling the successful design of high-efficiency, eco-friendly foam formulations that meet national standards.

Original authors: Yun Zhang, Zijie Yin, Yan Zheng, Fangting Tian, Yiming Xu, Zhongqing Liu, Zongheng Chen, Jieqing Zheng, Meiwei Huang, Yong Guo

Published 2026-06-29

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CC BY 4.0

Original authors: Yun Zhang, Zijie Yin, Yan Zheng, Fangting Tian, Yiming Xu, Zhongqing Liu, Zongheng Chen, Jieqing Zheng, Meiwei Huang, Yong Guo

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: The "Goldilocks" Foam

Imagine you are trying to put out a fire on a pool of oil. You throw a blanket of foam on top of it. This foam isn't just a fluffy cloud; it's a complex, wet sponge made of billions of tiny bubbles.

The secret to this foam working isn't just that it covers the fire; it's that it slowly "sweats" water onto the burning oil. This water creates a thin, protective film that stops the fire from breathing.

The problem? If the foam is too dry, it can't make enough water film. If it's too wet, it drains too fast and collapses before it can do its job. This study is all about finding the perfect "Goldilocks" zone for how fast that foam should drain its water.

The Ingredients: The Team Players

The researchers were testing a specific type of foam agent (AFFF) that uses a special "star" ingredient called STAR-2157/2470. To make this foam work, they mixed in other helpers:

K12 (The Heavy Lifter): Think of this as a surfactant that helps the foam hold its shape. The study found that adding a little bit of K12 helps the foam stay together longer. But, like adding too much salt to a soup, adding too much K12 actually makes the foam fall apart faster.
Xanthan Gum (The Thickener): This is a common food additive (used in ice cream to keep it smooth). In the foam, it acts like a thickener, making the liquid inside the bubbles sticky and slow-moving. This slows down the water draining out.
The Synergy: The researchers discovered that K12 and Xanthan Gum work together in a weird, non-linear way. You can't just add more of both to get better results. If you have a lot of thickener, adding more K12 doesn't help much. It's a delicate dance where the right mix is crucial.

The Heat Factor: Temperature's Double Personality

Foam doesn't just sit in a lab; it has to work on a hot fire. The researchers tested how heat changes the foam's behavior, and they found temperature plays a "double agent" role:

Scenario A: The Thick Soup (High Viscosity)
If the foam is thick (lots of Xanthan Gum), heat acts like a blender. As the temperature rises, the thick liquid gets thinner and runnier. This makes the water drain out faster. Heat always speeds things up here.
Scenario B: The Thin Water (Low Viscosity)
If the foam is thin (little to no Xanthan Gum), heat acts like a temporary bodyguard. A little bit of warmth helps the soap molecules move around and pack tighter, making the bubble walls stronger. This actually slows down the drainage at first. But if you keep heating it up (getting too hot), the liquid gets too thin, the walls break, and the foam collapses instantly.
- The Result: For thin foams, the drainage time goes up (gets slower) then down (gets faster) as it gets hotter. It's a non-straight line.

The Fire Test: Why Speed Matters

The team built 25 different foam recipes and tested them on a small oil fire. They measured two things:

Extinguishing Time: How fast did the fire go out?
Burnback Time: How long did it take for the fire to reignite after the foam was applied?

The Findings:

Too Slow: If the foam drains too slowly (too much thickener), the water can't reach the oil fast enough to make the protective film. The fire stays alive.
Too Fast: If the foam drains too quickly, the water film forms, but the foam structure collapses immediately. The fire reignites almost instantly.
Just Right: The researchers found a "sweet spot." For their specific foam recipe, the perfect time for 25% of the water to drain out was 5.9 minutes (give or take 12 seconds).

The Conclusion

The study proved that you can't just guess how to make fire-fighting foam. You have to engineer the drainage rate carefully.

By tweaking the amount of thickener (Xanthan Gum) and the helper surfactant (K12), and understanding how heat changes the mix, they successfully created two new foam formulas that met national safety standards. These formulas drain at the perfect speed: fast enough to put out the fire quickly, but slow enough to keep the fire from coming back.

In short: They turned the art of making fire foam into a precise science, finding that the best foam isn't the thickest or the thinnest, but the one that drains at exactly the right pace.

Technical Summary: Experimental Study on Foam Drainage of AFFF

Problem Statement
Aqueous film-forming foam (AFFF) extinguishes flammable liquid fires through a dual mechanism: the formation of a foam layer and a continuous water film supplied by foam drainage. While the foam layer provides initial coverage, the water film is not pre-existing; it relies on the dynamic drainage of liquid from the foam structure. In practical firefighting scenarios, the rate of foam drainage must be dynamically balanced with the rate of water film evaporation at high temperatures. If drainage is too slow, the foam lacks mobility and the water film is insufficiently replenished; if too fast, the foam layer collapses prematurely, leading to re-ignition. Current research has largely focused on single variables under ambient conditions, lacking a direct quantitative correlation between drainage kinetics, formulation composition, temperature effects, and actual fire-extinguishing efficiency. This study addresses the gap in understanding how formulation additives and ambient temperature regulate drainage to optimize AFFF performance.

Methodology
The study employed a systematic experimental approach involving formulation design, physical characterization, and fire-extinguishing validation:

Materials and Formulations: The study utilized a commercial fluoroether betaine surfactant (STAR-2157/2470) as the base. Various hydrocarbon surfactants (K12, CAB-35, APG0810, CTAB) and xanthan gum (as a foam stabilizer) were blended to create 16 initial formulations (Series B) and 4 temperature-study formulations (Series C). A final set of 25 formulations was designed to validate the drainage-performance correlation.
Physical Characterization: Surface and interfacial tensions were measured using a bubble pressure tensiometer and rotary drop tensiometer to calculate the spreading coefficient ( $S$ ).
Drainage Kinetics: A Dynamic Foam Analyzer (DFA100) was used to measure cumulative drained liquid volume, 25% drainage time, and liquid content at different heights. Foam microstructure (bubble size and shape evolution) was captured via imaging.
Temperature Regulation: A custom apparatus with a heated glass funnel and thermocouple array simulated the thermal effects of a hot oil surface. Tests were conducted at 26°C, 40°C, 50°C, and 60°C to analyze temperature coupling with formulation components.
Fire-Extinguishing Verification: Standardized fire-extinguishing tests were conducted on a 0.25 m² pan with 120# industrial solvent oil. Key metrics included extinguishing time ( $t_1$ ) and 100% burnback time ( $t_2$ ), compared against Chinese National Standard GB 15308−2006 ( $t_1 \le 1.2$ min, $t_2 \ge 10$ min).

Key Contributions and Results

Additive Synergy and Non-Linearity:
- Among hydrocarbon surfactants, Sodium Dodecyl Sulfate (K12) was found to be the most effective at delaying foam liquid separation, followed by CAB-35 and APG0810.
- A nonlinear synergistic effect was observed between K12 and xanthan gum. While both retard drainage, excessive addition of K12 (particularly in low xanthan gum concentrations) can actually accelerate drainage rather than delay it.
- Foam microstructure analysis revealed a negative correlation between initial bubble size and drainage time: smaller initial bubbles and higher initial liquid content ( $S_1$ ) resulted in better drainage retardation.
Dual Regulatory Mechanism of Temperature:
- The study identified a dual mechanism by which temperature affects drainage, dependent on the system's viscosity:
  - High-Viscosity Systems (with xanthan gum): Increasing temperature consistently accelerates drainage by reducing solution viscosity, thereby weakening the stabilizing effect of the polymer.
  - Low-Viscosity/Stabilizer-Free Systems: Temperature exhibits a non-monotonic effect. A moderate temperature rise (up to 40–50°C) initially delays drainage by enhancing the Marangoni effect and surfactant mobility, leading to a tighter interfacial film. However, further heating (to 60°C) reduces surface tension and accelerates film rupture, causing drainage to accelerate. Consequently, the 25% drainage time in these systems first increases and then decreases as temperature rises.
Quantitative Correlation with Fire-Extinguishing Performance:
- Fire-extinguishing experiments demonstrated that neither extremely slow nor extremely fast drainage is optimal.
- Formulations with very slow drainage (high xanthan gum) maintained long burnback times but failed to extinguish fires quickly due to poor foam mobility and insufficient water film replenishment.
- Formulations with very fast drainage (low xanthan gum) extinguished fires slowly or failed to maintain coverage, leading to short burnback times.
- Optimal Range: For AFFF formulations containing STAR-2157/2470, a 25% drainage time of 5.9 ± 0.2 minutes was identified as the optimal range to satisfy both extinguishing time and burnback time standards. Two specific formulations (ZY-14 and ZY-17) were successfully screened that met national standards ( $t_1 \le 1.2$ min, $t_2 \ge 10$ min) within this drainage window.

Significance
The paper claims to provide a foundational basis for designing high-efficiency and eco-friendly AFFF agents by establishing a quantitative relationship between drainage kinetics and fire-extinguishing performance. By validating that drainage rate must be controlled within a specific "sweet spot" rather than simply minimized, the study offers a formulation design strategy that moves beyond single-variable optimization. The identification of the dual temperature mechanism and the nonlinear synergy between K12 and xanthan gum provides critical insights for developing AFFF agents that remain effective under varying ambient and fire-surface temperatures. The successful screening of formulations meeting national standards using this drainage-control methodology confirms the practical utility of the proposed approach.