Structure And Flame-retardant Properties Of Environmentally-friendly Nonhalogen Flame Retardant Rigid Polyurethane Foam

Rigid polyurethane foams(RPUF),with excellent performance on thermal conductivity,mass and shock absorption,is widely used in heat insulation area.Unfortunately,the feature of flammability for RPUF limits its application.So flame retardant must be used in RPUF matrix to improve its flame retardant property.In this work,1-butyl-3-methyl-imidazole phosphate ionic liquid(IL)and 3-(N-diphenyl phosphate)amino propyl triethoxy silane(DPES),were prepared firstly.Then the influence of expanded graphite(EG),IL,EG modified with IL(IL-EG)and mixture of IL-EG and DPES(IL-EG/DPES)on the properties of RPUF,such as foam structure,thermal stability,flame resistance,micromorphology and mechanical properties,were investigated systematacially,and the mechanism of antiflaming was studied as well.Unmodified EG was added into the RPUF matrix and the mechanical properites,thermal stability and flammability of composites were investigated.The results showed that the average size of foams became large and nonuniform with the increase of EG content,and foams broken as well.The compression strength of RPUF observed a climbing tendency when loading EG by no more than 10 phr.Thermogravimetic analysis(TGA)revealed the initial decomposition temperature of RPUF declined by increasing EG,which means a bad performance on thermal stability.Meanwhile,flammability tests illustrated that the values of heat release rate(HRR),smoke release rate(SRR),total heat release(THR)and total smoke release(TSR)of RPUF all decreased with adding EG,and the time to ignition(TTI),limit oxygen index(LOI)were enhanced at the same time.Synthetically,EG could form an effective wormlike expandable charcoal isolated layer in RPUF matrix,which leads to an improvement of antiflaming performance for composites.A phosphonium flame retardant,1-butyl-3-methyl-imidazole phosphate ionic liquid(IL),was synthesised firstly,then the component and structure of IL were characterized by Fourier transform infrared spectrometer(FTIR)and 1H nuclear magnetic resonance spectrum(1H-NMR).The impacts of different IL contents on mechanical properties,thermal stability and flammability of RPUF composites were studied.The results indicated that IL could promote the formation of isolated charcoal layer on the surface of RPUF with the help of its decomposed products as phosphoric acid and metaphosphoric acid.This made an improvement on the performance of antiflaming for composites.Meanwhile,lots of noninflammability gases and free radical terminators(PO· or HPO·)would be obtained from the decomposition of IL.These exhibited as gaseous phase fire retardants could decrease the smoke release.The parameters of HRR,THR and TSR achieved the lowest values when adding IL with 15 phr,and TTI or LOI approached to the best points as well.On the other hand,the foams' average diameters got bigger when increasing IL continuously,which results in the worse performance on compression strength and thermal stability of RPUF composites.In general,the effect of improving antiflaming performance on RPUF by pure IL is not as good as that by pure EG.Modified fire retardant IL-EG was prepared firstly,and then mechanical properties,thermal stability and flammability of different RPUF/IL-EG composites were researched.The results revealed that RPUF filled with IL-EG presented better than pure EG or pure IL system in fire resistance at the same formula,which implies a good synergistic effect exists in the IL-EG system.IL could improve the interface compatibility among EG to RPUF matrix and catalyze the formation of residual charcoal to make a pyknotic and isolated layer.Besides,IL could release noninflammability gases and free radical terminators under degradation,which were good for the antiflaming properties of RPUF.In summary,with the increase of IL-EG content,the compression strength,LOI,TTI,HRR,THR,TSR of composites were all improved obviously unless the thermal stability.A N-P intumescent flame retardant,3-(N-diphenyl phosphate)amino propyl triethoxy silane(DPES),was synthesised and its structure was studied firstly through FTIR and 1H-NMR.After that,the properties of RPUF/IL-EG/DPES composites at different ratios were investigated systematically.The results presented that hydroxy on the surface of EG could react with –Si O(C2H5)of DPES,which made it easy to form isolated residual carbon layer.–NH of DPES could also react with isocyanate group of PAPI to improve the fire-retardant properties of composites.Meanwhile,the noninflammability gases and free radical terminators that come from the degradation of IL could also make a positive effect on the antiflaming feature of RPUF,as well as the release of poisonous gas,such as HCN,CO.When fixing the ratio of DPES/IL-EG at 1:1 with a totally content 20 phr,the values of LOI,THRR,THR were improved by 13.2%,60% and 45% respectively comparing to that of pure RPUF.The compression strength and thermal stability of RPUF composites were enhanced significantly at the optimum ratio,which implied a good synergistic effect.