Study On Aging Degradation Behavior And Lifetime Prediction Of Aqueous Film Forming Foam

Aqueous film forming foam(AFFF)is an effective extinguishing agent for liquid fuel(Class B)fires.The core component of AFFF is fluorocarbon surfactant.And hydrocarbon surfactant is usually added as foaming agents.In addition,the functional additives such as tackifier and cosolvent are generally added.Due to the high chemical stability of fluorocarbon surfactants,the storage life of AFFF is much higher than that of protein and synthetic foam.However,there are still risks of performance degradation and aging failure of AFFF during long-term storage.Therefore,it is necessary to study the aging and degradation behavior of AFFF under storage conditions and predict the performance changes at room temperature.In this thesis,a series of AFFF formulations were designed to establish the relationship between components and performance.The degradation behavior of the components of AFFF during aging was analyzed by accelerated thermal aging of the samples at 90 ℃.The time-temperature equivalence of AFFF aging was established based on the Arrhenius equation.And the performance change of AFFF during room temperature aging was predicted.(1)A series of AFFF formulations were designed by adjusting the formulation ratios of fluorocarbon surfactants,hydrocarbon surfactants and various functional additives.The p H,surface tension,viscosity,freezing point and foaming ratio of the samples were tested to establish the relationship between the components and performance of AFFF.With the increase of fluorocarbon surfactants concentration,the surface tension of AFFF decreases and the foaming ratio increases.With the increase of hydrocarbon surfactants concentration,the foaming ratio of AFFF increases.With the increase of viscosity increaser concentration,viscosity rises and foam ratio decreases.And the freezing point decreases with the increase of pour point depressant.(2)Accelerated aging of AFFF samples was performed at 90 ℃.The changes of p H,surface tension,viscosity,freezing point and foaming ratio were tested during the aging process.The changes of surfactants content after aging were characterized by liquid chromatography-mass spectrometry(LC-MS).And the accelerated aging of alkyl glycosides(APG),alkyl betaine(AAB)and modified cellulose was carried out in different p H environments.The results showed that during AFFF aging,the p H increased due to urea degradation,the viscosity decreased due to the degradation of modified cellulose,and the foaming ratio decreased due to the degradation of AAB and APG.The p H change of the solution has a significant impact on the degradation behavior.The p H rise caused by urea degradation will accelerate the degradation of APG,AAB and modified cellulose to varying degrees.(3)The AFFF samples were subjected to accelerated aging at60～90 ℃.The changes of p H,viscosity and foaming ratio during the aging process were tested.The time-temperature equivalence of AFFF aging was constructed using the kinetic fitting method and the time-temperature superposition method to predict the performance changes at room temperature.Comparing the prediction results with the data of natural aging,the time-temperature superposition method accurately predicted the p H and viscosity changes of room temperature aging,while the prediction results of the kinetic fitting method had some deviations.According to the prediction results of time temperature superposition method,after 8 years of storage at room temperature,the p H of AFFF samples will rise to 9.62,the viscosity will drop to 35.4 c P,and the foaming ratio will drop to 7.37 times.The p H of the sample no longer meets the relevant provisions of Chinese national standard.