Pyrolysis Kinetics And Flame Spread Characteristics Studies Of Typical Polymers

The pyrolysis and flame spread processes are two important studies during the initial and developing combustion stages respectively,which should be paid more attentions for their meaningful importance.Pyrolysis study of material is the fundamental of flame spread,and can determine the intensity of fire disaster.The radiation can be emitted from flame to pyrolysis surface,which will intensify materials pyrolysis speed.Materials' pyrolysis and flame spread draw lots of attentions from fire researchers.As commonly used functional materials,polymer materials are widely used in external thermal insulation system and inner-door decoration,which also makes them to be the most popular materials in fire research area.When polymer surface is exposed to external heat flux,these exposed materials can degrade and generate combustible gas,which can escape from materials' surface by bubbling.When generated combustible gas mixes with oxygen,the mixture gas can be easily ignited when meeting with spark.Meanwhile,the generated flame can transfer heat to pyrolysis surface in terms of heat conduction,convection,and radiation.Virgin materials will produce combustible gas continuously after be heated,when the combustible gas accumulates with high concentration,the front gas will be ignited by flame.Such procedure repeats over and over again,which is the step and mechanism of flame spread.Compared with other combustible solids like wood and cotton,polymers are synthesized artificially,easy to be ignited,and generate poisonous gases.Also thermoplastics materials burning will lead to melting and dripping phenomena,which will accelerate the flame spread process.Pyrolysis is the first step of materials' burning,while kinetics study is the fundamental study of pyrolysis.By materials' kinetics,we can explore the reaction rate and mechanism.In this study,we select XPS(extruded polystyrene)and PU(polyurethane)as representatives of one-step and multi-step reactions respectively to explore the polymer degradation kinetics.By genetics algorithm,each reaction could be separated from the total mass loss,and kinetics triplet of each reaction were also calculated.The calculated kinetics results were compared with traditional isoconversional kinetics method,including KAS method,FWO method,and Friedman method.The reactive and product mass loss variations were calculated theoretically,so to verify the accuracy of calculation,TG-MS and FTIR were employed to monitor the variation of these products.The theoretical and experimental results were compared eventually.For flame spread,we explore the sample size effects on horizontal and upward flame spread configurations theoretically and experimentally.Firstly,three typical polymers,PMMA,XPS and EPS were selected for horizontal flame spread testing.Different width and thickness were chosen,and lowest flame spread rate at a certain range of sample width was found for three materials.Then a flame spread model based on heat transfer feedback analysis was developed to explain the occurrence of this lowest flame spread rate.The model points that this lowest flame spread rate was caused by the competition of convection and radiation feedback,whose variation trend has the same variation with flame spread rate.Then PMMA sheets with different width and thickness were selected to conduct concurrent flame spread upwardly.And the results were compared with previous studies.For the reason that upward flame spread is mainly controlled by convection,which is driven by natural buoyancy.Then a model based on Reynolds hypothesis was developed to predict the mass loss rate.And a close prediction can be obtained compared with experimental results.This mass loss prediction model can be used for upward wall flame burning and horizontal forced flow burning.Finally,the dimensionless flame heights for horizontal and upward configurations were scaled with dimensionless heat release rate.