Study On The Modified Preparation And Anti-reignition Performance Of Hydrophobic And Oleophobic Superfine Ammonium Polyphosphate Dry Powder Fire Extinguishing Agent

Superfine dry powder fire extinguishing agent has become one of the most ideal alternatives of Halon fire extinguishing agent due to its high fire-extinguishing efficiency,environment friendly,good insulation,convenient use,and high security.However,superfine dry powder fire extinguishing agent has the great risk of re-igniting after putting out flammable liquid fires.Superfine dry powder fire extinguishing agent is generally treated by silicon oil to get a property of hydrophobicity.After the treatment,the surface of the particles is coated by a layer of very lipophilic film.When extinguishing an oil fire,the dry powder particles moving to the oil surface with the airflow will quickly sink into the bottom.Because of the little cooling effect of dry chemical,the high temperature of the oil pool drops slowly,causing the combustible vapor volatilizing continuously from the oil surface.Therefore,the local residual flame will spread rapidly to the whole oil surface and cause a reburning.The reburning of class B fire has always been a difficult problem in the application of dry powder fire extinguishing agent.Enhancing the anti-reignition performance of dry powder fire extinguishing agent is an important research direction of dry powder fire extinguishing agent.The re-ignition performance refers to the ability of fire extinguishing agent to suppress the reburning of combustibles for a long time after the fire is put out.Fluorocarbon surfactants are hydrophobic and oleophobic,which are commonly used in the preparation of hydrophobic and oleophobic materials.Previous studies have shown that fluorocarbon surfactant can enhance the anti-reburning performance of dry powder fire extinguishing agent.Fluorocarbon surfactant adsorbs on the surface of dry powder particles through hydrogen bond,which can improve the oil repellency of dry powder and make it float on the oil surface to form a sealing layer to isolate oxygen and inhibit fuel volatilization,so as to achieve the purpose of anti-reburning.However,due to the low binding energy of hydrogen bond,the hydrophobicity of anti-reburning dry powder modified by fluorocarbon surfactant is poor,which requires additional hydrophobic modification process of silicone oil.On the basis of previous studies,a fluorinated acrylate polymer was synthesized as fluorocarbon surfactant.By introducing silane coupling agent structural unit into the fluorocarbon surfactant,the superfine ammonium polyphosphate coated with silica was modified,and the fluorinated acrylate polymer was grafted onto the surface of ammonium polyphosphate particles.The hydrophobic and oleophobic superfine ammonium polyphosphate with good hydrophobic and oleophobic properties was successfully prepared.The main research works were as follows.(1)Selection and formulation optimization of fluorocarbon surfactant.Perfluorooctyl ethyl acrylate(FEA)and vinyltriethoxysilane(TEVS)were selected as fluoromonomers and functional monomers respectively.The effects of comonomers MMA,BA and SA on the modification results of fluoroacrylate polymer(FAP)were studied.The modification results of fluorocarbon surfactants synthesized by different comonomers were compared,and the best formula of fluorocarbon surfactant was selected for subsequent experiments.The effects of monomer ratio and addition amount of FAP on the hydrophobic and oleophobic properties of hydrophobic and oleophobic superfine ammonium polyphosphate(FMAPP)were studied.The optimum monomer molar ratio and addition amount of FAP were determined.(2)Preparation and characterization of hydrophobic and oleophobic superfine ammonium polyphosphate.There are two steps in the preparation process of hydrophobic and oleophobic superfine ammonium polyphosphate.The properties of FMAPP such as SEM,XPS,NMR,TGA and particle size were characterized.The surface morphology,surface composition,thermal degradation,particle size change and modification process of FMAPP were analyzed.(3)Tests on fire extinguishing performance and anti-reignition performance of hydrophobic and oleophobic superfine ammonium polyphosphate dry powder fire extinguishing agent.The fire extinguishing agent consists of FMAPP(80 wt%)and additive(20 wt%).The fire extinguishing performance and anti-reignition performance of hydrophobic and oleophobic superfine ammonium polyphosphate dry powder and ordinary ammonium polyphosphate dry powder were compared.It was found that hydrophobic and oleophobic superfine ammonium polyphosphate dry powder had better fire extinguishing performance and anti-reburning performance.The effect of oil temperature on the anti-reignition performance of hydrophobic and oleophobic superfine ammonium polyphosphate dry powder was studied.It was found that high oil temperature will lead to a rapid decline of oil repellency and loss of anti-rebuming performance in a short tim e.Low oil temperature has little effect on oil repellency and hydrophobic and oleophobic superfine ammonium polyphosphate dry powder still maintains anti reburning performance.The reasons for the decrease of oil repellency caused by high temperature are analyzed:on the one hand,the surface tension of aviation kerosene decreases with the increase of temperature;on the other hand,the high temperature intensifies the molecular thermal movement of fluorocarbon surfactant,which changes the structure of fluorocarbon chain orientation,resulting in the increase of surface tension of hydrophobic and oleophobic superfine ammonium polyphosphate dry powder.