Preparation Of Two Phosphorus-nitrogen Containing Flame Retardants And Research For Flame Retardant Epoxy Resins

Epoxy resins(EP)are widely used in electronics,electrical,chemical corrosion,machinery manufacturing,aerospace and other fields due to its excellent adhesion,corrosion resistance,electrical insulation and high strength.However,the epoxy resin thermosets are flammable,and there are critical scientific and application significance for endowing the thermosets excellent flame retardant performance.The additive flame retardant has the advantages of simple route and low cost for flame retardant EP thermosets.However,there are some disadvantages,such as the relative high loading amount and low flame retardant efficiency.With the rapid development of the electrical and electronic industry,the flame retardant EP materials with higher performance are required.Consequently,the preparation of flame retardant EP thermosets with low loading amount and high flame retardant efficiency has been concerned.In this paper,the intermediate of piperazine diphosphatethe was firstly prepared by the reaction of phosphoric acid and anhydrous piperazine,then the flame retardant of pyro/polyphosphoric acid piperazine defined as PPAP was prepared by dehydration polymerization of piperazine diphosphatethe at high temperature.The prepared PPAP was characterized by Fourier transform infrared spectroscopy(FTIR)and nuclear magnetic resonance(NMR).The results of thermogravimetric analysis(TGA)tests revealed that the initial thermal decomposition temperature of PPAP is 262 oC and the residual char was 16.4 wt% at 800 oC,which indicated that the synthesized PPAP possessed excellent thermal stability and charring capability.PPAP was incorporated into epoxy resins and cured with mphenylenediamine(PDA)to prepare flame retardant EP thermosets.The results revealed that the cured EP material passed UL-94 V-0 and the LOI value reached 30.5 %,which demonstrated that the obtained PPAP presented excellent flame-retardant efficiency for EP theromosets.The results of cone calorimeter tests revealed that the combustion parameters,such as the heat release rate(HRR),total heat release(THR),total smoke release(TSP)for EP/ 5 wt% PPAP thermosets were significantly reduced compared with that of pure epoxy resin.The TGA tests indicated that the introduction of PPAP promoted the thermosets decompose and charring ahead of time and the initial thermal decomposition temperature was decreased,however the thermal stability and residual char were enhanced at high temperature.The char residue for EP/ 5 wt% PPAP thermosets was increased from 14.4 wt% for pure EP to 21.0 wt% at 800 oC.Scanning electron microscopy(SEM)tests revealed that the incorporation of PPAP stimulated the EP material form a more continuous and compact char layer during combustion,which benefited to improve the flame retardancy for the EP thermosets.Another flame retardant polyphosphoric-boric acid piperazine defined as PPBAP was prepared,and the synthesized route as follow: firstly the intermediate phosphoric and boric acid piperazine was prepared from phosphoric acid,boric acid and anhydrous piperazine,the then PPBAP was obtained by dehydration condensation of intermidiate at high-temperature.The prepared PPBAP was characterized by FTIR and NMR.The TGA test revealed that the initial thermal decomposition temperature of PPBAP was 245.6 oC and the residual char was 18.6 wt% at 800 oC,which indicated that the obtained PPBAP flame retardant presented excellent thermal stability and charring capability.PPBAP was incorporated into epoxy resin cured with m-phenylenediamine(PDA)to prepare flame retardant EP thermosets.The tests results demonstrated that the thermosets passed UL-94 V-0 flamability rating with the LOI value of 31.9 %when the addition amount of PPBAP was only 4 wt%.The fact revealed that the obtained PPBAP flame retardant possessed superior flame retardant efficiency for epoxy resin thermosets,and the three flame retardant elements of phosphorus,nitrogen and boron presented excellent synergistic flame retardant effect for EP thermosets.Cone calorimeter tests revealed that the combustion parameters such as HRR,THR and TSP of EP/4 wt% PPBAP were significantly reduced compared with pure epoxy resin thermosets.The TGA tests indicated that the introduction of PPBAP stimulated the degradation and charring of the thermosets,and the initial thermal decomposition temperature of the composites was decreased.However,the thermal stability and charring capability of the composites were improved at 800 oC,and the residual char of thermosets was enhanced from 14.3 wt% of pure epoxy resin to 22.2 wt%.SEM tests revealed that the incorporation of PPBAP promoted the formation of a more continuous and compact char layer during combustion route,which efficiently inhibited the transmission of oxygen,heat and flammable gas during combustion,consequently the flame retardancy of the epoxy resins thermosets were enhanced.