Study On Flame Retardant Properties Of Phosphorus-boron Hybrid Polymer Epoxy Resin Composites

The hydroxy-terminated phospho-boron hybrid polymer（PBHP）were prepared with the method of the stepwise polymerization,which use dihydroxyglyceryl borate（DGB）and phenyl dichlorophosphate（PDCP）as starting materials.Phosphorus-boron element co-hybrid epoxy resin flame retardant composites（PBHP/EP）were prepared by pouring PBHP,epoxy resin（EP）and curing agent blend system into the mold and cross-linking;PBHP-MMT/EP flame retardant composites were prepared by pouring montmorillonite（MMT）,PBHP,epoxy resin and curing agent blend system into the mold and cross-linking.The molecular structure and relative molecular mass of PBHP were characterized through FT-IR,NMR and GPC.The thermal stability,flame retardancy and smoke release capacity of PBHP/EP and PBHP-MMT/EP flame retardant composites were tested using TG,LOI,horizontal and vertical combustion experiments,smoke density tester and microcalorimeter.The SEM and XPS were used to characterize the morphology and flame-retardant mechanism of the combustion carbon layer.The activation energies（E_a）of reaction pyrolysis were calculated by Flynn-Wall-Ozawa（FWO）theoretical calculation method.The difficulty of the pyrolysis reaction s were investigated.The effects of PBHP and PBHP-MMT systems on the flame retardant and mechanical properties of epoxy resin composites were studied.The results indicate that with the increase of the PBHP mass fraction,the material’s residual weight rate,LOI,UL-94 grade increase,and the total heat release（THR）,peak heat release rate（PHRR）,smoke density grade and elongation at break decrease.The tensile strength increases first and then decreases.When the mass fraction of PBHP is added to 15%,the THR and PHRR are reduced to 23.64 k J·g^-1、177.33 W·g^-1 respectively,LOI reaches 28.3%,UL-94 rating is V-0,the smoke density grade reaches 54,and under air and N₂ atmospheres the residual ratios are10.19%and 11.81%respectively;E_a of the composites increase with the conversion rate;the surface of the material combustion charcoa l layer is flat and dense;XPS shows that poly-phosphate,BPO₄,B₂O₃,and B₄C and other heat-resistant materials cover the surface of the carbon layer;the tensile strength is 35.21 MPa and the elongation at break is 2.42%.With the introduction of MMT,the THR,PHRR,smoke density grade,and elastic modulus of PBHP-MMT/EP composites decrease,and the residual weight ratio,LOI,UL-94 rating grade,and tensile strength of the material s increase;when adding MMT with a mass fraction of 3%to the 10wt%PBHP/EP,the smoke density is reduced to 46.2,the LOI is 29.1%,the tensile strength is 47.94 MPa,and the elongation at break is 5.35%.The E_a of the composite material increase with the conversion rate.A large number of MMT gathers and covers the surface of t he combustion charcoal layer.The comprehensive analysis shows that:PBHP is decomposed into polyphosphates and BPO₄ by heat,catalyzes the formation of carbon from matrix materials,and decomposes to form viscous glassy B₂O₃ and B₄C.Matrix carbon,B₄C and B₂O₃ form a barrier layer to prevent deep combustion and smog of materials release;PBHP-MMT has a significantly more synergistic flame-retardant and smoke-suppressing effect than PBHP,and proper addition of MMT is beneficial to improve the comprehensive mechanical properties of the material.