Synergistic Flame Retardant TPU Using Four Kinds Of Citrate With Ammonium Polyphosphate

TPU has high tensile strength and wear resistance,but its flammability limited its further application.Ammonium polyphosphate(APP)had been proved to have a good flame retardant effect on TPU,but there were still some problems,such as low flame retardant and smoke suppression efficiency,poor compatibility with TPU matrix and deterioration of mechanical properties of TPU composites.It was one of the important research contents in the field of fire safety materials to further improve the flame retardant and smoke suppression efficiency of APP to TPU through synergistic flame retardant technology.In view of the above problems,four kinds of citrate,such as nickel citrate(NC),cobalt citrate(Co C),copper citrate(Cu C)and yttrium citrate(YC),were synthesized in this paper,and further four kinds of citrate and ammonium polyphosphate(APP)flame retardant TPU composites were prepared.The flame retardancy and thermal degradation performance of TPU composites were studied by Cone calorimeter test(CCT),Scanning electron microscope(SEM),Laser Raman spectroscopy(LRS),X-ray photoelectron spectrometer(XPS),Limiting oxygen index(LOI),Vertical combustion test(UL-94),Thermogravimetric-Infrared spectroscopy(TG-IR)and Gas chromatography-mass spectrometry(GC-MS).The main conclusions were as follows:1.Study on flame retardant TPU with NC and APP.NC reduced the heat release and improved the char forming performance of TPU/APP composites.Compared with TPU/APP,the p HRR and THR values of TPU/APP/NC 0.125 decreased by 30.4 and71.7%respectively,and the char residues of TPU/APP/NC system were higher than that of TPU/APP by more than 70%.The char layer of TPU/APP/NC system was more compact and continuous,and the graphitization degree was further increased.Compared with TPU/APP,the char residue of TPU/APP/NC 0.5 under nitrogen and air increased by 22.8 and 33.6%respectively,and the thermal stability of the material was improved.The decomposition product of NC at high temperature was Ni O-Ni,which improved the strength and compactness of char residue.NC changed the decomposition process of TPU/APP,and reduced the amount of CO₂ and-NCO.2.Study on flame retardant TPU with Co C and APP.Co C reduced the heat release and the generation of smoke,and increased the graphitization degree of TPU/APP system.Compared with TPU/APP,the THR and p SPR values of TPU/APP/Co 0.125decreased by 56.8 and 31.5%,respectively,and the char residue increased by 35.2%.TPU/APP/Co C 0.5 had the highest FPI value(0.32 m²s/k W)and the lowest FGI value(2.16 kw/m²s).UL-94 of TPU/APP/Co C system had reached V-0 level.I_D/I_G value decreased from 3.23 of TPU/APP to 3.16,and the graphitization degree was increased.Compared with TPU/APP,the char residue of TPU/APP/Co C 0.5 under nitrogen and air were increased by 19.1 and 49.5%respectively.3.Study on flame retardant TPU with Cu C and APP.Cu C reduced the heat and smoke release of TPU/APP system.Compared with TPU/APP,THR and TSR of TPU/APP/Cu C0.125 decreased by 32.3 and 19.9%,respectively,and char residue increased by 58.7%.TPU/APP/Cu C 0.5 formed a denser char layer and the graphitization degree was increased.Cu C increased the LOI values of TPU composites,and the LOI values of TPU/APP/Cu C system were not lower than 26.5%;the char residue of TPU/APP/Cu C0.5 under nitrogen and air increased to 42.1 and 16.5%,respectively.4.Study on flame retardant TPU with YC and APP.YC improved the char-forming performance of TPU/APP system and reduced the release of heat,smoke,CO and CO₂from TPU composites.Compared with TPU/APP,the values of THR,TSR,CO peak release rate and CO₂ peak elease rate of TPU/APP/YC 0.5 decreased by 49.3,15.3,44.8and 48.6%respectively.The char residues of TPU/APP/YC system were more than 70%higher than that of TPU/APP.TPU/APP/YC 0.5 formed a more compact and smooth char layer,which played the role of heat insulation and smoke suppression;The LOI value of TPU/APP/YC 0.5 increased to 27.5%.Compared with TPU/APP,the char residue of TPU/APP/YC 0.5 under nitrogen and air increased by 34.9 and 50.5%respectively.In summary,citrate effectively reduced the heat and smoke hazards of TPU/APP system.Citrates were decomposed into metal oxides at high temperature,which promoted the decomposition of APP and generated polyphosphoric acid(salt),catalyzed the carbonization of TPU,changed the structure of condensed char layer,improved the compactness and graphitization degree of char layer,and then formed the thermal insulation char layer,thus obtained the good flame retardant efficiency and smoke suppression performance.