Preparation Of Functionalized Hydrotalcite-Graphene Oxide Hybrids And Study On Their Flame Retardant Effect In TPU

Hydrotalcite?LDHs?,as a traditional inorganic additive flame retardant,it has been widely used in the field of flame retardant polymers due to its unique chemical structure and the controllability of laminate and interlayer ions.In this paper,Graphene oxide?GO?was prepared by modified Hummers method,and NO₃^--LDHs-GO hybrids was synthesized through co-precipitation method.Then,Mo₇O₂₄^6--LDHs-GO,SA?NH₂SO₃^-?-LDHs-GO and SDS(C₁₂H₂₅SO₃^-)-LDHs-GO hybrids were fabricated throughionexchangemethod,respectively.Additionally,the AY36(C₁₈H₁₄N₃SO₃^-)-LDHs-GO hybrids were prepared by one-step method.The structure and morphology of these materials were characterized by X-ray diffraction?XRD?,fourier transform infrared spectroscopy?FTIR?,scanning electron microscope?SEM?.Subsequently,a series of thermoplastic polyurethane?TPU?composites were prepared by using them as flame retardants.The dispersion,flame retardant,smoke suppression and thermal stability properties of TPU composites were studied by SEM,cone calorimeter test?CCT?,smoke density test?SDT?,thermogravimetry-fourier transform infrared spectroscopy?TG-FTIR?,respectively,and the law of smoke generation and the formation of carbon layer in the combusion process were investigated.The following conclusions are obtained through experiments and analysis:?1?The analysis results of hybrids shown that the GO with sheet like morphology was synthesized successfully through modified Hummers method,the well-crystallized NO₃^--LDHs were fabricated by co-precipitation method.Mo₇O₂₄^6--LDHs,SA-LDHs and SDS-LDHs and their corresponding hybrids were synthesized by ion exchange method.Additionally,C₁₈H₁₄N₃SO₃^-was intercalated into the interlayer space of LDHs through the one-step procedure to obtain AY36-LDHs and AY36-LDHs-GO hybrids.?2?The SEM images of the fractured surface for TPU composites indicated that the simple intercalation modification can improve the dispersibility of hydrotalcite to a certain extent;the hybrids can be perfectly embedded in the polymer with better dispersion,which confirmed that the loading of LDHs on GO nanosheets can further improve the compatibility with the polymer matrix.?3?Mo₇O₂₄^6--LDHs and Mo₇O₂₄^6--LDHs-GO hybrids can improve the flame retardant and smoke suppression properties of TPU composites.With the introduction of Mo element,MoO₃ can absorb smoke particles due to its high smoke suppression performance,which makes the molybdate intercalation series hydrotalcites show good smoke suppression effect.Furthermore,with increasing content of GO in hybrids,the thermal and smoke parameters of composites show a decreasing trend.TPU5containing 20 wt%Mo₇O₂₄^6--LDHs-5%GO has the best flame retardant and smoke suppression effect,the pHRR₁ and pHRR₂ are 328.7 kW/m² and 340.5 kW/m²,respectively.The total smoke release?TSR?value decreases from 674.2 m²/m²of pure TPU to 313.8 m²/m²,a decrease by 53.5%.The presence of GO in hybrids can play a remarkable synergistic flame retardant and smoke suppression role with Mo₇O₂₄^6--LDHs.Mo₇O₂₄^6--LDHs-5%GO hybrids can further improve the thermal stability of TPU by increasing the carbon residue and delaying the decomposition rate.?4?SA-LDHs and SA-LDHs-GO hybrids can also improve the flame retardant and smoke suppression properties of TPU composites to a certain extent.However,the synergistic flame retardancy between LDHs and GO is not obvious when the GO content in the hybrids is low.Similarly,with increasing content of GO in hybrids,the flame retardant and smoke suppression properties of TPU composites increase gradually.This is mainly attributed to the following reasons.On the one hand,GO can isolate the transmission of heat,adsorb smoke particles and free radicals.On the other hand,it can promote more organic structures to participate in the carbonization process,remain in the condensed phase rather than being burned in the gas phase.?5?The flame retardant and smoke suppression efficiency of SDS-LDHs and SDS-LDHs-GO hybrids are obviously better than that of NO₃^--LDHs.And even when GO content is low in hybrids,it can still show synergistic effect of flame retardant and smoke suppression between the SDS-LDHs and GO.TPU5 containing 20 wt%SDS-LDHs-5%GO has the best flame retardant and thermal stability properties among all the samples,the pHRR and TSR are 238.5 kW/m² and 354.7 m²/m²,respectively,which are 32.1%and 19.0%lower than TPU2 containing the same mass fraction SDS-LDHs,and the formed char residue is thicker and denser.?6?AY36-LDHs and AY36-LDHs-GO hybrids can also improve the fire safety of TPU composites.Similar to C₁₂H₂₅SO₃^-,the structure of SO₃^-in C₁₈H₁₄N₃SO₃^-can be used as acid source to further promote charring and improve the quality of carbon layer.Moreover,the structure of non-fused naphthalene and anthracene ring in C₁₈H₁₄N₃SO₃^-can absorb more heat during thermal decomposition,so it shows excellent flame retardant and smoke suppression properties.The total heat release?THR?value of 20 wt%AY36-LDHs is 85.6 MJ/m²,a decrease by 12.6%compared with the same mass fraction NO₃^--LDHs.When AY36-LDHs-5%GO was added,the thermal and smoke parameters of the composite were further reduced,and the thermal stability was also improved to a certain extend.In conclusion,the intercalation modified hydrotalcite-graphene oxide hybrids can further improve the dispersion in the TPU matrix,and the synergistic effect between LDHs and GO can further enhance the flame retardant and smoke suppression efficiency.