Preparation Of Rare Earth Based DOPO Derivative Flame Retardant And Its Application In Polymer Materials

Traditional intumescent flame retardants（IFR）have some problems,such as low flame retardant efficiency and large amount of addition,so the development of new intumescent flame retardant system has become a research hotspot.Due to the particularity of the 4f orbital,rare earth ions have the ability to catalyze organic reactions such as hydrogenation,dehydrogenation,and esterification.It can be used as excellent flame retardant synergists for IFR.In this study,piperazine pyrophosphate（PAPP）and ammonium polyphosphate（APP）were integrated as IFR,and rare earth-based phosphaphenanthrene（DOPO）derivatives were utilized as flame retardant synergists.A new type of intumescent flame retardant system was designed and developed to improve the flame retardant properties of polypropylene（PP）and polylactic acid（PLA）.The main work is as follows:1.PAPP and APP were employed as IFR system to explore the synergistic flame retardant effect of IFR with different ratios on wollastonite reinforced polypropylene（WPP）.The results shew that the vertical combustion grade of flame retardant composites passed UL94 V-0 and the limit oxygen index（LOI）increased to 36.2%when the total amount of IFR is 30 wt%and the mass ratio of PAPP to APP is 1:1;Compared with pure WPP,the total heat release（THR）and total smoke release（TSR）of flame retardant WPP were significantly reduced,and there was an obvious synergistic flame retardant effect between PAPP and APP.In addition,the flame retardant composite had excellent rigidity,and the elastic modulus was increased by 49.7%compared with WPP.IFR significantly improved the thermal stability of WPP,inhibited the degradation of the polymer,and the carbon residue rate reached 39.6%at 800°C in an air atmosphere.Scanning electron microscopy-energy dispersive spectroscopy（SEM-EDS）,Raman spectroscopy and Fourier transform infrared spectroscopy（FTIR）were used to analyze the residual carbon after combustion.The results shew that IFR promoted the formation of continuous dense carbon layer and improved the graphitization degree of carbon layer.The charring effect and dilution effect of PAPP and APP in condensed phase and gas phase made the flame retardant composites shew excellent flame retardant properties.2.Cerium based DOPO derivative（Ce@DDP）was synthesized by hydrothermal method from（6H-dibenz[c,e][1,2]oxaphosphorin-6-ylmethyl）-p-oxide-butanedioic acid（DOPO-DDP）and Ce（NO₃）₃·6H₂O.And its chemical composition was verified by a series of tests,its chemical structure was proposed.Then,the flame retardant PP composites with different proportions were prepared by melt blending method with the mass ratio of 1:1 PAPP and APP as IFR and Ce@DDP as flame retardant synergist.The flame retardancy and combustion properties of PP composites were characterized by LOI,UL94 vertical combustion and cone calorimetry.The results shew that the LOI value of the flame-retardant PP composite with 17 wt%IFR and 1 wt%Ce@DDP reached33.8%and passed the UL94 V-0 grade;the peak heat release rate（PHRR）and the peak smoke release rate（PSPR）were reduced.IFR/Ce@DDP could significantly improve the thermal stability of PP,and the carbon residue rates were 8.8%and 14.1%at 800°C under argon and air atmospheres,respectively.By analyzing the residual carbon after combustion,the possible flame retardant mechanism was speculated.In the condensed phase,IFR/Ce@DDP catalyzed the formation of carbon layer,and cerium in Ce@DDP changed valence at high temperature(Ce⁺³/Ce⁺⁴),which improved the oxidation resistance and graphitization degree of carbon layer.In the gas phase,the non-combustible gas produced by IFR decomposition diluted the concentration of oxygen and combustible gas.Finally,it led to significant synergistic flame retardant effect.3.Lanthanum DOPO derivative（La@DDP）was synthesized from DOPO-DDP and La（NO₃）₃·6H₂O by solution synthesis,and their chemical structure and surface morphology were characterized.PAPP and APP with a mass ratio of 1:1 was integrated as IFR.IFR and La@DDP form a new IFR system,and flame-retardant PLA composites with different ratios were prepared by melt blending method.When the total amount of IFR and La@DDP is 6 wt%（IFR/La@DDP=3/1）,the LOI value of the flame-retardant PLA composite was 32.0%and passed the UL94 V-0 level.Compared with pure PLA,PHRR and THR were reduced by 31.0%and23.2%,respectively.Thermogravimetric analysis studies shew that the carbon residue rate of the compound flame-retardant system at 600°C was significantly improved compared with that of the single flame-retardant system under argon and air atmospheres,indicated that IFR and La@DDP had obvious synergistic effect on catalytic carbonization.Through the analysis of residual carbon,it is found that the carbon layer formed after compound flame-retardant system combustion was smoother and denser,and the degree of graphitization was higher.It was speculated from the experimental data that there were dilution effect and free radical capture effect in gas phase,and catalytic charring effect in condensed phase during the combustion process of the composite flame retardant system,and the combined action of the three aspects led to the result of high-efficiency flame retardant.In addition,the PLA/IFR/La@DDP system has a excellent retention rate of mechanical properties,which can satisfy the flame retardancy of PLA while considering the mechanical properties.