Preparation Of New Phosphazene-hydrotalcite Composite Flame Retardant And Its Flame Retardancy To Epoxy Resin

Epoxy resin（EP）,as an important thermosetting polymer material,is widely used in many industries and fields,but it is very easy to burn and a large number of toxic and harmful gases will be produced during the combustion process.Therefore,the research and development of a new type of flame retardant epoxy resin with high efficiency and environmental protection has become one of the research hotspots in the field of flame retardant.In this thesis,modified hydrotalcite（Mg Al Zn-LDHs-PMo A）containing both Mo and P flame retardant elements in the interlayer was prepared by reconstruction method,and then used in epoxy resin matrix cooperated with a cyclotriphosphonitrile derivative containing active amino group（HACP）.After that,the enhancement effect of components on flame retardant and smoke suppression of epoxy resin was studied,and the flame retardant and smoke suppression mechanism of composites was also discussed.Specific studies include:（1）Hydrotalcite Mg Zn Al-LDHs-CO₃ containing Mg,Zn and Al three metal elements was synthesized by constant p H coprecipitation method,and then heteropoly acid anion(PMo₁₂O₄₀^3-)was successfully inserted into the interlayer of hydrotalcite Mg Zn Al-LDHs-CO₃by reconstruction method to synthesize a new hydrotalcite Mg Zn Al-LDHs-PMo A flame retardant.Its structure and morphology were characterized by Fourier transform infrared（FT-IR）,X-ray diffraction（XRD）and scanning electron microscope（SEM）.The study of thermal stability shows that the addition of Mg Zn Al-LDHs-PMo A flame retardant will reduce the initial degradation temperature of EP composites and significantly increase the final carbon residue.The cone calorimetric test showed that with the addition of 5wt%Mg Zn Al-LDHs-PMo A flame retardant,the total heat release（THR）and peak heat release rate（PHRR）of EP composites decreased by 13.6%and 43.3%,respectively.In addition,the total smoke production（TSP）of EP composites was also reduced by 24.5%.The comprehensive results show that the hydrotalcite flame retardant modified by heteropoly acid anion PMo₁₂O₄₀^3-intercalation can obviously improve the flame retardant and smoke suppression properties of EP.（2）Hexa（4-aminophenoxy）cyclotriphosphazene（HACP）,a cyclotriphosphazene derivative containing active amino group,was synthesized from hexachlorocyclotriphosphazene and p-nitrophenol by substitution and reduction,and its structure was characterized by FTIR,¹H NMR and ³¹P NMR.The results of flame retardant study of HACP on EP show that when the addition was only 5wt%,the value of LOI reached29.2%,and there was no droplet phenomenon.Cone calorimetric data showed that the total heat release（THR）and total smoke production（TSP）decreased by 15.9%and 5.2%,respectively.The carbon residue of EP/HACP composites after combustion was analyzed by SEM and XRD.The results show that the amount and compactness of carbon residue have been significantly increased,indicating that HACP can preferentially degrade to form phosphorus-containing compounds at lower temperatures to accelerate the carbonization of epoxy resin,and then improve the flame retardancy.（3）Mg Zn Al-LDHs-PMo A and HACP were used as flame retardants of epoxy resin by blending.TG test showed that the residual carbon content of EP composite at 800℃was much higher than that of pure EP,which indicated that the synergistic effect between the two flame retardants could improve the thermal stability of EP.According to the analysis of LOI and UL-94 tests,when the addition of the two flame retardants is only 5wt%,EP can reach the standard of non-flammability.Cone calorimetric test showed that the THR,PHRR and TSP of EP composites with two kinds of flame retardants were greatly reduced.When the total addition of flame retardants was 7wt%,THR,PHRR and TSP decreased by 35.2%,50.9%and 43.9%compared with pure EP,respectively.The addition of composite flame retardants can effectively reduce the heat release of EP composites,and can also play a significant role in smoke suppression.Through the SEM,XRD and Raman analysis of the residual carbon,the flame retardant mechanism was further studied.The results show that the two flame retardants can accelerate the catalytic carbonization of epoxy resin and form a dense protective carbon layer to isolate the mutual transfer of combustible gas,oxygen and heat.Furthermore,the addition of flame retardants can also reduce the release of pyrolysis products in the gas phase,which shows that the two flame retardants have double flame retardant effect in gas phase and condensed phase,thus reducing the hazard of fire.Among them,the continuous oxidation and reduction of two metal oxides Mo O₂ and Mo O₃ produced by Mo element at high temperature can reduce the release of reducing gases（CO and H₂,etc.）to a certain extent,which has important application value for reducing fire hazard.