Research On The Key Technology For Preparation Of Red Mud Based Layered Double Hydroxides/Polyurethane Efficient Halogen-free Flame Retardant Composite

Due to the wide range of compositions possible,TPU is one of the most useful commercial classes of polymers and have found extensive use in both industrial production and daily life.But as same as other polymer materials,TPU suffers a serious disadvantage of poor stability towards fire and heat.Therefore,developing a new type of flame retardant TPU composite will become the key research in the future.In order to solve these problems,red mud based layered double hydroxides(LRM),bis(4-nitrophenyl)phosphate(BNPP)modified LRM material(BRL),Ammonium phosphate monobasic modified LRM material(PRL),layered yttrium hydroxides(LYH)and graphene oxide supported layered yttrium hydroxides(GO-LYH),were synthesized by a co-precipitation route firstly.Their structure and morphology were characterized by X-ray diffraction(XRD),Fourier transform infrared spectra(FTIR),Nuclear magnetic resonance spectra(NMR),Transmission electron microscope(TEM),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS)analysis.Then,LRM/TPU,BRL/TPU,PRL/TPU,LYH/TPU and GO-LYH/TPU composites were prepared by a melt-blending method.The flame retardancy,smoke suppression and thermal stability of the TPU composites were evaluated using cone calorimeter test(CCT),smoke density test(SDT)and thermo-gravimetric analyzer test(TGA).All kinds of LDH samples have good crystal structure and correct functional group demonstrated by the XRD,FTIR and NMR results.TEM and SEM results revealed that the dispersion of modified LDH was better than that of unmodified LDH because the eliminated strong interaction of hydrogen bonds between oxygen-containing groups in GO,phosphate groups in BRL,PRL materials and hydroxyl groups.CCT and TGA results illustrated a significant improve of the flame retardancy and thermal stability in all LDH/TPU composites.Specifically,the PHRR values of LRM/TPU,BRL/TPU,PRL/TPU,LYH/TPU,GO-LYH/TPU composites were 644.22 kw/m~2,524.36 kw/m2,420.52 kw/m2,392.54 kw/m2,350.76 kw/m2,which gave a 41.60%,52.46%,61.79%,67.42%,70.88%reduction compared with TPU sample;the char residue content of TPU composites reached 7.78%,13.90%,16.34%,13.85%,14.59%,increased by 2.09%,8.21%,10.65%,9.13%,9.77%compared with TPU sample.As seen in SDT results,the total smoke generation of TPU samples was significantly decreased except LYH/TPU composite.The luminous flux of each samples were as follows,LRM/TPU:19.9%,BRL/TPU:44%,PRL/TPU:43.2%,LYH/TPU:3.1%,GO-LYH/TPU:12.8%,which increased by 17.8%,41.9%,41.1%,1.2%,10.9%than TPU sample.Finally,the char residues after CCT test were analyzed by XRD and SEM-EDS.The improved flame retardancy and smoke suppression were attributed to the catalytic carbonization of LDH and the physical barrier of char layer indicated by char analysis.In soild phase,LDH can help to promote charring and forming compact char layer.The dense protective char layer could block smoke particles,slow down heat flow transfer from fire to the underlying material and finally delay the degradation of the base material.Furthermore,in gas phase,the P-radicals generated by BRL and PRL also have a positive impact on the flame retardancy of TPU composites.