High-temperature decomposition chemistry of trimethylsiloxane surfactants, a potential Fluorine-Free replacement for fire suppression

Per-and polyfluoroalkyl substances (PFAS) have become global environmental contaminants due to being notori-ously difficult to degrade, and it has become increasingly important to employ suitable PFAS alternatives, especially in aqueous film-forming foams (AFFF). Trimethylsiloxane (TriSil) surfactants are potential fluorine-free replacements for PFAS in fire suppression technologies. Yet because these compounds may be more susceptible to high-temperature decomposition, it is necessary to assess the potential environmental impact of their thermal degradation products. Our study analyzes the high-temperature degradation of a truncated trimethylsiloxane (TriSil-1n) surfactant based on quantum mechanical methods. The degradation chemistry of TriSil-1n was studied through radical formation and propagation initiated from two prominent pathways (unimolecular and bimolecular reactions) at both 298 K and 1200 K, a relevant temperature in flames and thermal incinerators. Regardless of the pathway taken and temperature, all radical intermediates stemmed from the polyethylene glycol chain and primarily formed stable poly-dimethylsiloxanes (PDMS) and small organics such as ethylene, formaldehyde, and acetaldehyde, among other products. The major degradation products of TriSil-1n resulting from high-temperature thermal degradation as predicted by this study would be relatively less harmful to the environment compared to PFAS incineration/com-bustion products from previous research, supporting the replacement of PFAS with TriSil surfactants.

Automated summary

This study analyzed the high-temperature degradation of a truncated trimethylsiloxane (TriSil-1n) surfactant and found that the degradation products of TriSil-1n are relatively less harmful to the environment compared to PFAS incineration/combustion products from previous research, supporting the replacement of PFAS with TriSil surfactants.