| Polyethylene and polypropylene are the two most widely used general plastics.Manufacturers usually add flame retardants for flame retardant treatment.The pyrolysis and combustion characteristics of flame retardant materials will change compared with pure polymers,so exploring the pyrolysis and combustion characteristics of different flame retardant polymers is of great value for understanding the development and spread of fire in the process of fire investigation.Based on this,eight typical commercial flame retardants,including bromine,intumescent,inorganic phosphorus and nitrogen flame retardants,were selected to prepare flame retardant polyethylene and flame retardant polypropylene samples and carried out pyrolysis and combustion experiments.Taking the flame-retardant samples as the research object,the flame-retardant performance was preliminarily verified by vertical combustion grade test,and the flame-retardant performance of the flame-retardant samples was greatly improved.Then,the pyrolysis weight loss law of the samples was studied by thermogravimetric analyzer.It was found that with the increase of heating rate,the pyrolysis temperature of the samples increased as a whole,the mass residual rate of all intumescent flame retardant samples increased,and the mass residual rate of inorganic phosphorus flame retardant samples decreased（except MRP flame retardant samples）.Compared with pure samples,the peak pyrolysis rate and initial decomposition temperature of most flame retardant samples decreased in varying degrees.After pyrolysis,all bromine and nitrogen flame retardant samples had no mass residue,and the intumescent and inorganic phosphorus flame retardant samples had residual carbon.The pyrolysis temperature and peak value of pyrolysis rate of polypropylene samples were lower than that of polyethylene samples as a whole,and the decomposition temperature of most flame retardants was significantly lower than that of polyethylene,which was close to that of polypropylene and had a higher matching degree.The activation energy of the samples was calculated by Kissinger and FWO method,and the relative deviation of the results was less than 10 %.The law of pyrolysis weight loss of the samples could also provide a reference for judging the flame retardant composition of the materials.The pyrolysis products were analyzed by pyrolysis gas chromatography/mass spectrometry.The total ion flow diagram of polyethylene samples were in the form of "triple peak".Among them,the short chain hydrocarbons of bromine flame retardant samples decreased and the long chain hydrocarbons increased.The hydrocarbon content of intumescent flame retardant samples was the lowest.The short chain hydrocarbons of inorganic phosphorus flame retardant samples decreased,but the long chain hydrocarbons did not increase.The hydrocarbon composition of nitrogen flame retardant samples was close to that of pure polyethylene samples.The content of aliphatic hydrocarbons in polypropylene flame retardant samples decreased significantly and the content of alicyclic hydrocarbons increased significantly.Among them,the content of alicyclic hydrocarbons in bromine flame retardant samples was the highest.The content of alcohols and ketones in intumescent flame retardant samples was the highest.Inorganic phosphorus flame retardant samples had less cyclic products,but higher alcohol and ketone content.Alicyclic hydrocarbons in nitrogen flame retardant samples increased,but aliphatic hydrocarbons did not decrease significantly.There were also some characteristic products in the pyrolysis products of flame retardant samples,which are helpful to trace the flame retardant components of materials and provide a basis for determining the cause of personnel poisoning.Then the combustion behavior of the samples was studied by cone calorimeter.The peak value of heat release rate of flame retardant samples decreased,and the heat release rate of different samples showed different characteristics（such as double peak curve of intumescent flame retardant samples,front single peak curve of inorganic phosphorus flame retardant samples,and rear single peak curve of nitrogen flame retardant samples）.The total heat release of flame retardant samples was lower than that of pure sample,and the total heat release was reduced.The effective heat of combustion showed that the average value of bromine flame retardant samples decreased the most,and the flame retardant effect in gas phase was the best.Except for all bromine flame retardant samples and polyethylene inorganic phosphorus flame retardant samples,the peak smoke production rate of other flame retardant samples decreased.Among all flame retardants,only intumescent and nitrogen flame retardants reduced the peak value of polymer CO release rate.Finally,based on the combustion behavior parameters,the fire risk evaluation model was constructed by analytic hierarchy process-entropy weight method.It was found that the comprehensive fire risk of bromine flame retardant samples was the highest,followed by intumescent and inorganic phosphorus flame retardant samples,and nitrogen flame retardant samples were the lowest,indicating that the possibility of casualties near bromine flame retardant materials is high,and nitrogen flame retardant materials is low. |
