Study On Preparation Of Rare Earth Layered Double Hydroxides/Graphene Oxide Hybrids And Their Flame Retardancy In TPU

As a kind of versatile engineering thermoplastic,thermoplastic polyurethane?TPU?has played an important role in many industrial fields due to its good processability,high mechanical strength,outstanding wear resistance and excellent adhesion,which is widely used in the production of films,hoses,cables and conveyor belts,etc.However,the high fire hazard of TPU,including the high flammability with melt dripping phenomenon,and the large amount of visible smoke and toxic gases produced during combustion process,still poses a great challenge to its large-scale application.Therefore,in order to broaden the application of TPU,it is necessary to improve the flame retardancy and smoke suppression of TPU.In this paper,three rare earth layered double hydroxides?LDHs?and their hybrids with graphene oxide?GO?were synthesized as flame retardants by hydrothermal method with rare earth ions:La³⁺,Eu³⁺and Y³⁺.Their structure and morphology were characterized by X-ray diffraction?XRD?,fourier transform infrared spectroscopy?FTIR?,energy dispersive spectroscopy?EDS?and transmission electron microscopy?TEM?.Then,a series of TPU composites were prepared via adding the as-prepared samples into TPU matrix through melt blending method.Meanwhile,the flame retardancy,smoke suppression and thermal stability of TPU composites were comprehensively investigated in detail by cone calorimeter test?CCT?and thermalgravimetric analysis?TGA?.The XRD results showed that hydroxides would appear in LDHs when the concentration of rare earth ions were too high.The FTIR,EDS and TEM results exhibited that rare earth ions were intercalated into the LDHs laminates,and its molar ratio to Al3+is close to 0.05.Simultaneously,rare earth LDHs were also loaded on the GO layers,which indicates three rare earth LDHs/GO hybrids were both successfully synthesized.The CCT results confirmed that La-LDHs/GO,Eu-LDHs/GO and Y-LDHs/GO all had good flame retardancy and smoke suppression performance on TPU than those of MgAl-LDHs and rare earth LDHs without GO.Compared with pure TPU,the peak heat release rate?PHRR?values of TPL2,TPE2 and TPY2 were decreased by 33.1%,29.3%and 31.3%respectively,and the peak smoke production rate?PSPR?values were decreased by 51%,50%and 43%respectively.The TGA results indicated that three rare earth LDHs/GO hybrids could reduce the thermal decomposition temperature of TPU,increase the char yield and improve the thermal stability in varying degrees.The results of char residues analysis exhibited that the rare earth LDHs/GO hybrids can enhance the strength of carbon layer and promote the carbon layer to be more complete,which is attributed to the catalytic carbonization effect of rare earth LDHs and the physical barrier effect of GO.Through the comprehensive comparison of the flame retardancy,smoke suppression and thermal stability of three rare earth LDHs/GO hybrids,the La-LDHs/GO with the best performance were selected to be mixed with zinc borate?ZB?to investigate the synergistic mechanism of flame retardancy and smoke suppression.The CCT results showed that the PHRR,total heat release?THR?and PSPR values of TPZ3?containing 8 wt%ZB and 2 wt%La-LDHs/GO?were 379kW/m²,116.6 MJ/m² and 0.039 m²/s respectively,which were significantly lower than those of TPU composites containing only ZB and combination of 0.05 La-LDHs and ZB.The results of char residues analysis showed that the existence of La-LDHs/GO can make the porous carbon layer promoted by ZB become smooth and compact,thus protecting TPU matrix more effectively.