Study On Flame Retardant Of Polyurethane Foam Modified By Layered Double Hydroxides

Flexible polyurethane foam is a unique organic polymer material,which has been widely used in various fields due to its excellent performance of heat insulation,high rebound and sound absorption.However,flexible polyurethane foam burns easily in air,which will cause fire accident.And it greatly limits the application of flexible polyurethane foam.Therefore,it is particularly necessary to study the flame retardant property of polyurethane foam in order to reduce the probability of fire accidents caused by polyurethane foam.As people’s awareness of environmental protection is gradually strengthened,the preparation of green flame retardants has gradually become an important research direction in the field of material flame retardants.In this paper,inexpensive and environmentally friendly hydrotalcite compounds were selected as flame retardants.The dihydrogen phosphate was inserted into carbonate Mg-Al hydrotalcite layer by ion exchange method.And then the thermal stability,flame retardant and smoke suppression properties of flexible polyurethane foams with modified hydrotalcite were investigated.The modified hydrotalcite was characterized by X-ray diffraction（XRD）and the results showed that the dihydrogen phosphate root intercalation was successful.Five different heating rates were selected to carry out TG analysis tests on the samples,and the three methods of Coats-Redfern,Flynn-Wall-Ozawa and Kissinger were also used for pyrolysis kinetics analysis.The results showed that the thermal stability of the sample was improved and the sample was not easy to be decomposed when the activation energy of the sample increased after modification.When the amount of flame retardant was 15%,the initial decomposition temperature of the foam was increased by 25℃ and the carbon residue quantity was increased by 9%.The flame retardant property of modified polyurethane foam was researched by limiting oxygen index method and cone calorimeter test.The LOI of the blank sample was only 17%and its LOI increased to 25.4%when the modified hydrotalcite added amount reached 15%.The peak heat release rate（PHRR）of the sample decreased by 74.9kW/m2 and the total heat release（THR）decreased by 9.7MJ/m2 when the heat radiation intensity was 35kW/m2.The results showed that the formation of dense carbon layer was promoted by the addition of phosphorus to the hydrotalcite modified by dihydrogen phosphate root intercalation during the combustion of flexible polyurethane foam,which played an excellent flame retardant effect.By comparing the effects of different amounts of flame retardants on the polyurethane foam,it was concluded that 15%of modified hydrotalcite was the most appropriate amount.The types and concentrations of poisonous and harmful gases in the modified samples were measured by cone calorimeter test,smoke density chamber and flue gas analyzer.The total amount of flue gas released by the modified sample after combustion was reduced by 157.7m2/m2,and the maximum concentration of carbon monoxide（CO）gas decreased from 51.3mg/m3 to 23.8mg/m3.On the basis of the data obtained,the addition of modified hydrotalcite significantly reduced the concentration of flue gas and inhibits the formation of harmful gases such as CO.