Synthesis Of A Novel Phosphazene-based Flame Retardant Containing Active Amine Groups And Its Application In Epoxy Resin

Epoxy resin（EP）has been applied in various of fields due to their unique mechanical properties,chemical stability and moisture resistance.However,EP must be treated with flame retardants in some key areas.Therefore,it is of great significance to develop a high-efficiency flame retardant which has good compatibility with EP.Phosphazene flame retardants are widely used in the field of flame retardant because of their advantages of non-toxicity and high thermal stability.Therefore,a reactive-type flame-retardant additive（PBFA）containing active amine group was obtained by using hexachlorocyclotriphosphazene（HCCP）and N-Aminoethylpiperazine as raw materials.PBFA was then added to EP,the flame-retardant efficiency and thermal stability were studied by limiting oxygen index（LOI）tests,vertical burning tests（UL 94）,cone calorimeter tests（CCT）and thermogravimetry analysis（TGA）,respectively.Moreover,the generated gas phase and residual char were analyzed to explore the flame-retardant mechanisms.The metal nickel ion(Ni²⁺)was introduced to the surface of PBFA through the chelation of active amino groups to synthesize PBFA-Ni²⁺flame retardant,then PBFA-Ni²⁺was incorporated into EP.Exploring the effect of Ni²⁺on flame-retardancy,smoke-suppression and catalysis of char formation effects through comparing with the same addition amount of PBFA.The details contents are listed as follows:Part one:PBFA was obtained by nucleophilic substitution reaction,and the molecular structure was characterized by Fourier transform infrared（FT-IR）,solid-state ³¹P nuclear magnetic resonance(³¹P NMR)and X-ray photoelectron spectroscopy（XPS）.It is then added to the EP,it was found that when adding amount of PBFA reached 9 wt%（named as EP/PBFA-9.0）,the sample had the highest flame-retardant efficiency.The LOI value of EP/PBFA-9.0 sample can reach to 29.0%;the sample can pass the UL 94 V-0 test.The TGA results demonstrated that the incorporation of PBFA can decrease the onset decomposition temperature,while the amount of residual char of EP/PBFA-9.0 was improved by 6.95%compared with that of pure EP at 800^oC.The results of CCT showed that the peak heat release rate（PHRR）,total heat release（THR）and total smoke production（TSP）of EP/PBFA-9.0decreased by 46.70%,29.30%and 48.04%,respectively.Gas chromatography-mass spectrometry（GC-MS）analysis of gases released during the degradation of pure EP and EP/PBFA-9.0 samples showed that PBFA can significantly reduce the amount of flammable substances released from EP,thereby inhibits the combustion.The analysis of char residue by FT-IR and scanning electron microscopy（SEM）showed that PBFA could promote the formation of dense protective char layer in EP,and the P=N bond structure in PBFA still remained in residual char,demonstrating that PBFA can play a fire-resist role in the condensed phase.The mechanical tests results showed that a certain amount of PBFA can improve the tensile strength of EP.Part two:Based on the first part of the synthesized PBFA,Ni²⁺was chelated to the surface of PBFA to obtain PBFA-Ni²⁺flame retardant.The energy spectrum（EDS）analysis was used to detect the presence of Ni²⁺,and the content of Ni²⁺was characterized by EDTA titration experiment.PBFA and PBFA-Ni²⁺were added to EP in an amount of 6 wt%to obtain EP/PBFA-6.0 and EP/PBFA-Ni²⁺-6.0.The results showed that only EP/PBFA-Ni²⁺-6.0 passed the UL 94 V-0 test and its LOI value reached 27.7%.The results of CCT showed that the PHRR of EP/PBFA-Ni²⁺-6.0 decreased by 41.02%compared with that of pure EP.For THR and TSP,EP/PBFA-Ni²⁺-6.0 was also lower than that of pure EP by 28.48%and 22.74%,respectively.As for carbon monoxide production rate（COP）and carbon dioxide production rate（CO₂P）,the peaks of EP/PBFA-Ni²⁺-6.0 were reduced by 34.50%and 45.60%,respectively.As for char residue,EP/PBFA-Ni²⁺-6.0 sample is 19.58%higher than that of pure EP,the above results fully demonstrate that the introduction of Ni²⁺has a good catalyzing effects on the char formation of EP.The analysis of residual char by Raman spectroscopy showed that EP/PBFA-Ni²⁺-6.0 achieves the highest degree of graphitization,as well as the denser char layer.The TGA results showed that the introduction of Ni²⁺lead to a significant delay in the temperature at which the sample reaches the maximum decomposition rate,thus enhances the protection of the matrix to a certain extent.