Investigation On Seawater-resistant Aqueous Film-forming Foam Based On Short-chain Fluorocarbon And Hydrocarbon Surfactants

Aqueous film-forming foam(AFFF)can form a closed water film and foam layer on the surface of hydrocarbon fuels during the fire extinguishing process.The dual function of foam and water film quickly controls and extinguishes fire.It was considered to be the most efficient fire extinguishing technology for large-scale open-air liquid fires.AFFF was not only used on land but also widely used in offshore workplaces.As AFFF was promoted worldwide,people have gradually discovered that perfluorooctane sulfonate(PFOS)is contained in the long-chain fluorocarbon surfactants which are the core component of AFFF.PFOS can seriously pollute the environment and threaten the survival of animals and plants.As a result,the application of traditional AFFF has been greatly restricted.In response to this problem,domestic and foreign researchers have committed to finding or developing alternatives to the long-chain fluorocarbon surfactants and hoped to develop a new environmentally friendly AFFF.So far,researchers have focused on the development of fluorine-free formulations,or substituting short-chain fluorocarbon surfactants for long-chain ones.However,the existing research is far from mature,and the performance of the formulations needs to be improved.For the fluorine-free formulations,it is impossible to form a water film on the surface of the liquid fuel,so they have been out of the category of "aqueous film-forming foam".Fluorine-free foams are mainly suitable for fighting forest fire or other solid fires.Therefore,our research will focus on the short-chain fluorocarbon surfactants,and developing AFFF formulations based on the short-chain fluorocarbon and hydrocarbon surfactants system.Then,testing and evaluating the performance of the AFFF formulations,in addition to taking into account the seawater resistance of the formulations.The main research contents and results are as follows:(1)Research on the short-chain fluorocarbon and hydrocarbon surfactants system and AFFF formulations.Determining the types and concentration of fluorocarbon and hydrocarbon surfactants are the basis for developing AFFF formulations.For this reason,two short-chain fluorocarbon surfactants with high surface activity(FS-50 and Cap1157),were selected through literature research and preliminary experiments.The two are compounded with anionic(SDS and AOS),nonionic(APG0810)and amphoteric(CAB-35)hydrocarbon surfactants,respectively.By testing the surface activity,viscosity and foam properties of the single surfactants and the mixed systems,determining the appropriate concentration range of short-chain fluorocarbon and hydrocarbon surfactants in AFFF formulations.Formulating AFFF formulations,and conducting fire extinguishing and burn-back experiments,and then screening the formulations according to the national standard(GB15308-2006).The results show that there was a synergistic interaction between FS-50 and the four hydrocarbon surfactants.The surface activity and foam properties of the mixed systems were significantly improved.The reason is that FS-50 changes the micellar aggregation behavior of the hydrocarbon surfactants,promoting the improvement of the performance of the mixed system.It is found that the series of AFFF formulations based on FS-50/APG0810 systems have the best performance and when the foaming ratio is between 7-10,the fire extinguishing and burn-back performance of the formulations are the best.(2)Research on the influence of inorganic salts on the performance of short-chain fluorocarbon and hydrocarbon surfactants system.To better explore the seawater resistance of the AFFF formulations,we selected three main inorganic salts in seawater(CaCl2,KCl and NaCl),and deeply explored the influence of three inorganic salts on the surface activity and foam properties of FS-50/SDS,FS-50/APG0810 and FS-50/CAB-35 systems.The results show that CaCl2,KCl and NaCl had almost no effect on the surface activity and foam properties of FS-50/APG0810 and FS-50/CAB-35 systems.While FS-50/SDS system was greatly affected by the inorganic salts:three inorganic salts enhanced the surface activity of the system;CaCl2 and KCl significantly weakened the foaming and foam stability of the system,whereas NaCl had little effect on the foam properties of the system.In addition,this study revealed the foam stabilizing and defoaming mechanism of CaCl2 and KCl on SDS(anionic hydrocarbon)foam:low concentration defoamed due to "bridging" effect of KDS,and high concentration stabilized foam because forming the crystals KDS and Ca(DS)2 blocked the plateau border.(3)Research on the effect of artificial seawater on the performance of three typical AFFF formulations.According to the effects of three inorganic salts on the performance of the short-chain fluorocarbon and hydrocarbon surfactants system,we further explored the effect of artificial seawater on the performance of AFFF formulations based on FS-50/SDS,FS-50/APG0810 and FS-50/CAB-35 systems.The results show that the performance of AFFF containing FS-50/SDS system was greatly impaired by seawater,while the formulations based on FS-50/APG0810 and FS-50/CAB-35 systems could better resist the adverse influence.The reason for this is the inorganic salts in seawater could not decrease the concentration of nonionic or amphoteric hydrocarbon surfactants.In particular,the AFFF formulations based on FS-50/APG0810 system showed excellent performance whether they were diluted with deionized water or artificial seawater.