Preparation And Properties Investigation Of Flame Retardant Thermoplastic Polyurethane Elastomer Composites Based On Iron Tailings

Nowadays,the accumulation of iron tailings not only occupies valuable land resources,but also causes serious environmental pollution,which seriously affects the safety and property of human life.Therefore,the high value utilization of iron tailings has become a focus.Thermoplastic polyurethane(TPU)is widely used in many fields due to its excellent comprehensive performance,but it has the shortcomings of easy combustion,melting dripping and large amount of toxic flue gas release,which seriously restrict the wide application of TPU.Thus,it is urgent to improve the fire safety performance of TPU.Based on this,the comprehensive utilization of iron tailings and flame retardant modification of TPU were combined in this thesis.Iron tailings and their derivatives were used as flame retardants for TPU.The high value utilization of iron tailings and the comprehensive improvement of fire safety performance of TPU composites were realized.This thesis.mainly performs from the following three aspects:(1)The flame retardant effect of iron tailings in TPU materials;(2)Investigation of synergistic flame retardant effect for iron tailings and traditional flame retardants in TPU materials;(3)The metal hydroxide and jarosite fabricatd from iron tailings and used as flame retardant for TPU.Flame retardant TPU composites were prepared by melt blending method and solution method.Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),X-ray fluorescence spectroscopy(XRF),thermogravimetric analysis(TGA),cone calorimeter(CCT),micro calorimeter(MCC),scanning electron microscopy(SEM)and Raman spectroscopy were used to systematically investigate the effects of modified iron tailings,metal hydroxides and jarosite on the thermal stability,flame retardancy,smoke suppression and smoke&toxicity gases reduction of TPU composites.The main results are shown as follows:(1)Silane coupling agent KH550 was used to modify iron tailings to prepare modified iron tailings(MIT),and the MIT was further added into thermoplastic polyurethane(TPU)by melt blending technology to prepare a series of polyurethane elastomer/modified iron tailings composites(TPU/MIT).The results shown that MIT can improve the thermal stability of TPU composites,and the addition of 10 wt%MIT increases the activation energy of TPU composites to 90 KJ/mol from 58.4 KJ/mol of pure TPU.TG test confirmed that,the char residue of TPU/MIT30 at 700 ^oC was enhanced to 32.17 wt%compared with 3.13 wt%of pure TPU.Cone calorimeter(CCT)test showed that 30 wt%MIT could reduce the heat release rate(HRR),total heat release(THR),smoke production rate(SPR)and total smoke release(TSR)of TPU by39%,23.5%,37.5%and 37.8%,respectively.Raman spectroscopy of char residue showed that MIT can significantly improve the strength and graphitization degree of the char residue,and increase the thermal stability of the char residue,thus enhaning fire safety of TPU composites.(2)Aluminum hypophosphite(AHP)and MIT were formed into a synergistic system.On this basis,a series of TPU/AHP/MIT composites were prepared by melt blending method.The results showed that the addition of AHP alone can reduce the initial decomposition temperature of TPU composites and promote the carbonization of TPU matrix.After MIT was used to coordinate with AHP.The thermal stability of TPU/AHP/MIT composites was improved.Compared with TPU/AHP25,the residual carbon at 700 ^oC of TPU/AHP22.5/MIT2.5 composites increased by 7.6%.The thickness of expanded carbon layer increases obviously,and the total smoke production(TSP)decreased by 32.8%.The production of toxic gases such as CO decreased significantly.Thermogravimetric-Fourier infrared spectroscopy(TG-FTIR)results showed that the addition of MIT could significantly reduce the total gas product release during the combustion of TPU/AHP/MIT composites.Carbon slag analysis showed that the combination of MIT and AHP can reduce the pore structure of carbon layer,and improve the compactness and graphitization degree of carbon layer.And it could also enhance the thermal stability and heat insulation and oxygen insulation ability of carbon layer.Based on the above analysis conclusions,the mechanism of AHP/MIT synergistic flame retardant TPU was proposed.(3)Ammonium polyphosphate(APP)and MIT were combined into a synergistic system.On this basis,a series of TPU/APP/MIT composites were prepared by melt blending method.TG test showed that the synergistic effect of APP and MIT could significantly increase the char residue of TPU/APP/MIT composites and improve the thermal stability of the char layer.Cone calorimetry test showed that,PHRR and THR of TPU/APP15/MIT10 decreased by 33.9%and 79.3%compared with those of TPU/APP25,while the peak values of CO and CO₂ release rates were decreased by69.26%and 90.34%,and the total smoke release(TSR)was decreased by86.17%.SEM-EDX,Raman spectroscopy and FTIR of char residue showed that the synergistic effect of APP and MIT can effectively improve the graphitization degree of char layer,promote the formation of aromatic structure,P-O-C and P-O-P bond in the char layer,effectively improving the compactness of char layer,and inhibiting the transportation of oxygen,gaseous products and heat during combustion,and thus improving the fire safety performance of TPU/APP/MIT composites.(4)Magnesium hydroxide,calcium hydroxide and jarosite were prepared from iron tailings.The three flame retardants were used alone or combined with APP and AHP to enhance flame retardancy of TPU by melt blending method and solution method.The results shown that the addition of 4 wt%magnesium hydroxide,calcium hydroxide and jarosite can reduce the THR of TPU composites by 17.9%,18.5%and 25.3%,respectively,and effectively reduce the CO release strength of TPU composites during combustion.The cone calorimetry test showed that the combination of jarosite and AHP or AHP could effectively reduce release strength of gaseous products for TPU composites,thereby improving the fire safety performance of TPU composites.