Preparation And Characterization Of Phosphorus Flame Retardants With Aromatic Structure And Their Effects On Flame Retardancy And Smoke Suppression Of Epoxy Resin

Epoxy resin(EP)is a commonly used thermosetting resin.Due to its special molecular structure and properties,it is widely used in aerospace,automotive machinery,sporting goods and other fields.However,epoxy resin is flammable,accompanied by a large amount of black smoke and toxic gases such as CO and NO in the combustion process,which limits its application in many aspects.In order to develop high-performance epoxy resins(EP),Four new phosphorus flame retardant polyol polymers with aromatic structure,such as PODOE,PODSE,PSDSE,PSDOE were synthesized by melt blending from 9,10-dihydro-9-oxaphenanthr-ene-10-oxide(DOPO),itaconic acid(ITA),phosphorus pentasulfide(P₂S₅),and p-benzoquinone(HQ)as reactants.The molecular structures of the four polymers were characterized by Fourier transform infrared spectroscopy(FTIR),~1H NMR,¹³C NMR and ³¹P NMR.The thermal stability of the four polymers was analyzed by thermogravimetry(TG).The carbon residue of PODSE and PSDSE at 700?is higher than that of PODOE and PSDOE.The reason is that the structure of polyol contains sulfur,which helps to improve its thermal stability and charring ability.Add PODOE alone or compound APP to EP to explore the modification of flame retardant and smoke suppression of EP.The thermal stability,combustion and mechanical properties of EP composites were analyzed by TG,limiting oxygen index(LOI),vertical combustion(UL-94)and mechanical tests.The results show that both PODOE and PODOE/APP can promote the carbonization of EP,slow down the thermal degradation behavior of EP composites and improve their thermal stability.When PODOE/APP is added,the combustion performance is improved,and UL-94 can reach V-0 level.Compared with PODOE,PODOE/APP system modified EP composites have stronger mechanical capacity.Cone calorimetry(cone)test,cone calorimetry infrared spectroscopy(CC-FTIR),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS)and Raman spectroscopy(Raman)were used to analyze the flame retardancy and flame retardant mechanism of EP materials.The results show that PODOE/APP can effectively reduce the heat release rate(HRR),total heat release(THR),smoke generation rate(SPR)and total smoke release(TSR)of EP matrix materials,The safety and fire resistance of EP composites are improved.PODOE decomposes phosphoric acid,polyphosphate and esterifiable polyols after heating,which can promote the dehydration and cross-linking of EP materials into carbon,and the carbon residue layer can effectively inhibit the release of flue gas and heat transfer.At the same time,the thermal decomposition of NH₃and CO₂ by app can reduce the generation and release of volatile combustibles in the gas phase,so that the material has good flame retardant and smoke suppression effects.PODSE and PSDOE were separately added to EP to modify the flame retardancy of EP.The results showed that when the addition amount was 20%,the LOI values of PODSE and PSDOE were 25%and 28.5%respectively,but UL-94 only reached grade V-1.T_5%,T_50%and T_max in the two decomposition stages of the two flame retardant systems have the same changes,and there are obvious differences in the amount of carbon residue.Both flame retardants can effectively inhibit the release of smoke and the generation of heat.There are many pores on the surface of PODSE-EP residual carbon,and the carbon layer generated by PSDOE-EP is more dense and has better shielding effect.According to the analysis of Raman and XPS,there are differences in the flame retardant mechanism between the two flame retardants.PSDOE generates more polyphosphate and pyrophosphoric acid compounds,which makes EP composites have better carbonization ability.A large number of PODSE and PSDOE will agglomerate in EP,which destroys the continuity between intermolecular chains and weakens the interaction between molecules,thus affecting the mechanical properties of the composites.PSDSE was compounded with APP to form a composite flame retardant,which was added to EP to explore the flame retardant effect and smoke suppression effect of synergistic flame retardant of nitrogen,phosphorus and sulfur.The results show that the charring ability and thermal stability of PSDSE/APP are stronger than that of PSDSE.After adding PSDSE/APP,the flame retardant effect changes significantly,and UL-94 can reach V-0 level.The addition of PSDSE/APP can effectively reduce the heat generation of EP matrix and inhibit the release of smoke.Through the further study of residual carbon by TG-FTIR,SEM,XPS and Raman,it is found that some phosphorus containing compounds(S=P-O)produced by PSDSE in the condensed state promote the formation of carbon and form a physical protective layer,so that the material has a good smoke suppression effect.APP will decompose and produce some sulfur-containing and nitrogen-containing non combustible gas(SO₂,NH₄)products,Oxygen dilutes the combustion of combustible gases in the surrounding environment.The EP composite has better flame retardant effect.