Synthesis And Properties Of Phosphorus-containing Benzimidazolyl Flame Retardants

Epoxy resin(EP for short)as a kind of polymer material has been widely used in many fields.However,its shortcomings such as flammability,violent combustion and a large amount of toxic smoke have great safety risks.Therefore,it has become more urgent to improve the flame retardant properties of EP.The flame retardant properties of EP can be improved by adding flame retardant or introducing flame retardant elements into EP structure.The main research work of this paper is as follows:(1)Taking p-hydroxybenzaldehyde,diphenyl chlorophosphate and o-phenylenediamine as raw materials,a new reactive flame retardant containing phosphorus/nitrogen binary hybrid was prepared through substitution and condensation reaction:Phosphoric acid 4-(1H-benzimidazol-2-yl)-phenyl ester diphenyl ester(PBIm).The chemical structure of PBIm was determined by nuclear magnetic resonance(NMR)and infrared spectroscopy(FTIR).It is introduced into EP matrix by chemical bonding.The fire safety performan ce and thermal stability of EP/PBIm polymeric materials were analyzed by thermogravimetric analysis(TGA),limiting oxygen index(LOI),vertical combustion(UL-94)and cone calorimeter(CCT).The test results show that after adding 20 wt%PBIm,the carbon residue content of EP/PBIm polymer at 800°C increased to 33.4%,which reduced its thermal weight loss rate and improved the thermal stability of the system.The LOI of EP/PBIm polymer is as high as 26.9%,passing UL-94 V-1 level,and the peak heat release rate(PHRR)and total heat release(THR)of EP/PBIm-3 polymer are 390.6k W/m~2 and 69.4MJ/m~2,which decreased by 62%and 28%compared with EP/BI m polymer,respectively.Therefore,the introduction of PBIm into EP matrix improves the thermal stability and flame retardant properties of EP/PBIm polymeric materials.(2)Using PBIm and copper acetate-hydrate as raw materials,the phosphorus/nitrogen binary hybrid PBIm was flame-retardant modified,and the phosphorus-containing benzimidazole-based copper complex flame retardant(PBIm-Cu)was synthesized.The chemical structure and microstructure of PBIm-Cu were analyzed by FTIR,X-ray photoelectron spectroscopy(XPS),elemental analysis(EDS)and scanning electron microscopy(SEM).The effects of PBIm-Cu on the thermal stability,flame retardan cy and smoke suppression properties of EP materials were investigated by TGA,LOI,UL-94 and CCT.The test results show that,compared to 5%PBIm/EP composite material,5%PBIm-Cu/EP composite material has a lower maximum weight loss rate and higher residu al carbon content,indicating that PBIm-Cu/EP composite material has higher The heat resistance.The LOI value of7%PBIm-Cu/EP composite is 31.6%,and the vertical combustion test reaches UL-94V-1 grade.In addition,the HRR,THR and TSP of PBIm/EP and PBIm-Cu/EP composites are significantly lower than pure EP.Among them,the PHRR,THR and TSP of 5%PBIm-Cu/EP are 735.5 k W/m~2,65.7 MJ/m~2 and 23.8 m~2,respectively,which are respectively 3.3%,8.2%and 1.7%lower than 5%PBIm/EP.The PHRR and THR of the 7%PBIm-Cu/EP composite material are 604.8 k W/m~2 and 60.2 MJ/m~2,respectively,which are 64%and 41%lower than pure EP.Raman spectroscopy(Raman),SEM and FTIR were used to analyze the carbon layer of poro us crosslinked structure.The results showed that PBIm-Cu had flame retardant effect in both gas phase and condensed phase,and thus had flame retardant and smoke suppression effect.The mechanical analysis shows that the Young's modulus of PBIm-Cu/EP composite material has increased significantly.(3)Using PBIm as the organic functional group,the PBIm-Ni complex flame retardant was prepared by reacting with nickel acetate tetrahydrate.Its structure and morphology were analyzed by NMR,FTIR,XPS and SEM.The PBIm-Cu complex and PBIm-Ni complex were added into the epoxy resin in different proportions to improve its thermal stability and fire resistance.The effects of the ratio of PBIm-Cu and PBIm-Ni on the thermal stability and flame retardant properties of the composites were investigated by using TGA,LOI and CCT.When the mass ratio of PBIm-Cu complex to PBIm-Ni complex is 1:3,the carbon residue of the composite material(EP6)is higher than other materials,and the weight loss rate is the lowest.PHRR and THR of EP6 composite were 801.6 k W/m~2 and 62.6 MJ/m~2,respectively,which decreased by 52.6%and 38.8%compared with pure EP,respectively.It was found that the ratio of PBIm-Cu to PBIm-Ni was 1:3 to achieve the best flame retardant effect.Through Raman spectroscopy and SEM analysis of residual carbon,the flame-retardant mechanism of epoxy resin was studied.