Synthesis Of Novel Organophosphorus Flame Retardant And Its Application In Epoxy Resin

Epoxy resin(EP)has been used in various fields because of its excellent properties.However,EP is flammability.In China,many fire incidents of EP factories had been happened in recent years,which indicates that it is necessary to study about flame-retardant EP materials.In addition,EP is fragile,easy to age and has the need for transparency in some specific applications.Therefore,it is very important to develop high efficient flame retardants of EP while ensuring its mechanical properties.Moreover,further attention should be paid to the optical transparency,curing activity and photoaging resistance of EP.Considering the environmental problems and flame retardancy,organophosphorus flame retardants have been widely studied.In this work,three new phosphorus-containing flame retardants were synthesized,the flame retardancy,thermal stability and mechanical properties of EP/PEPAEDTMP,EP/PI-DTPMP and EP/HP-DOPO were studied,the flame retardancy mechanism was explored,and further attention was paid to EP/HP-DOPO’s transparency,curing activity and light-aging resistance.The main results of this paper are as follows:(1)A new flame retardant PEPA-EDTMP was synthesized by the reaction of PEPA with ethylenebis(nitrilodimethylene)tetraphosphonic acid(EDTMP),and applied to EP.Compared with the pure EP,the LOI value of EP/5%PEPA-EDTMP increased from 26.3% to 32.1%,and result of the UL-94 test increased from no grade(NR)to V-0.In the CCT test,the total heat release(THR)and total smoke release(TSR)decreased by 13.4%and 43.2% respectively and the char residue increased,showing good flame retardancy of EP/5%PEPA-EDTMP.At the same time,due to the interfacial force between PEPA-EDTMP and EP matrix,the mechanical properties of EP/PEPA-EDTMP composites were improved with a small amount of addition.However,the addition of PEPA-EDTMP slightly reduced the crosslinking density of EP matrix so the tensile strength(Ts)of the material showed a slight decrease with the introduction of 5wt%PEPA-EDTMP.In addition,the hydrogen bond between PEPA-EDTMP and matrix weakened the force between the molecular chains of EP to a certain extent and increased the free volume of polymer.As the result of that,the toughness of EP /PEPA-EDTMP composite was slightly improved.(2)Piperazine hexahydrate(PI)and diethylenetriamine penta(methylene phosphonic acid)(DTPMP)are used to synthesize flame retardant PI-DTPMP through supramolecular reaction.The incorporation of PI-DTPMP simultaneously improves the mechanical and flame retardant EP.With only 5 wt% loading of PI-DTPMP,EP composites show excellent flame retardancy with a LOI of 36.4% and V-0 rating in the UL-94 test.The cone calorimetric test results demonstrate that PHRR,THR and TSR of EP/5%PI-DTPMP are reduced by 44.9%,34.7% and 37.7%compared with that of pure EP,respectively,owing to the formation of compact char layer during combustion.Moreover,EP/PI-DTPMP composites show enhanced mechanical properties with the improved tensile and impact strength,as well as higher storage modulus,crosslink densities and glass transition temperatures in dynamic mechanical analysis.(3)Aiming to develop high performance flame-retardant epoxy resin(EP),a novel phosphorus-containing flame retardant named 6-(3-(2-hydroxyphenyl)propyl)dibenzo[1,2]oxaphosphinine 6-oxide(HP-DOPO)was synthesized and employed as a multi-functional additive for EP with simultaneously flame retardation,excellent transmittance,mechanical enhancement and anti-aging.With 5% loading of HP-DOPO,EP composites showed outstanding flame retardancy with a high LOI value of35.6% and V-0 rating in UL-94 test.The cone calorimetric test results demonstrated that the peak heat release rate and total heat release of EP/5%HP-DOPO were reduced by 40.4% and 32.6%,respectively.Compared with pure EP,the resultant EP/5%HP-DOPO exhibited superior mechanical properties with 27.9% and 56.2% increase in tensile and impact strengths,respectively.Furthermore,the active hydrogen atom of HPDOPO reacted with the alkyl radical(R·)or peroxide radical(ROO·)produced by EP in the oxidation process to inhibit aging.The exploration of this novel multi-functional additive provided a powerful basis for the potential industrial applications of high-performance flame-retardant EP.