Synthesis Of Organic-hypophosphite And Its Flame-retardant Application In Epoxy Resin

In recent years,organic-hypophosphate flame retardants,represented by alkyl phosphates,have attracted wide attention due to its advantages of good thermal stability,low addition and charring ability.In this thesis,the synergistic barrier effect between alkyl phosphate-aluminum poly-hexamethylenephosphinate(APHP)and phosphate ester in epoxy resin has been researched.Inspired by this,a nitrogen-containing organic hypophosphatetri-3-(aluminum phosphinate)-propyl-1-triazine-trione(TAHP)was synthesized and applied into epoxy resin with an adding-type triazine-containing phosphaphenanthrene compoundtri-(3-DOPO-1-propyl)-triazide(TAD),and the flame retardant behavior and mechanism of TAHP/TAD in epoxy resin were also explored.In addition,TAHP was further compounded with three reactive-type phosphaphenanthrene compounds,respectively,and their flame retardant effect were also researched.The main research contents are as follows:(1)Two flame retardants,APHP and bisphenol-A bis(diphenyl phosphate)(BDP),were incorporated into diglycidyl ether of bisphenol A(DGEBA)thermoset with 4,4?-diaminodiphenyl sulfone(DDS)as curing agent,and then the synergistic flame retardant behavior and mechanism were also investigated.The results showed that: compared with thermosets containing 10 wt% APHP and 10 wt% BDP alone,3.3%APHP/6.7%BDP/EP/DDS possessed a better flame retardant properties since its limited oxygen index(LOI)value increased and passed the V-0 rating in UL94 test.The cone calorimeter test revealed that pk-HRR of 3.3%APHP/6.7%BDP/EP was significantly inhibited and the time to pk-HRR was also delayed.During combustion,the binary system of APHP/BDP released less flammable fragment into gas phase and formed more phosphorus-rich residues in condensed phase,indicating a significant synergistic barrier protection effect.The char layer with better flame-retardant barrier effect efficiently weakened the burning intensity and postponed heat release,endowing epoxy thermosets with a better flame-retardant performance.(2)A novel organic-hypophosphite flame retardant TAHP was synthesized via the addition reaction between triallyl isocyanurate(TAIC)and hypophosphorous acid,and the molecular structure of TAHP were characterized and confirmed.Then,TAHP with phosphaphenanthrene derivative TAD was applied to DGEBA cured using 4,4?-diaminodiphenylmethane(DDM).The synergistic flame retardant behavior and mechanism of TAHP/TAD were also investigated.Compared with 4% TAHP/EP and 4% TAD/EP samples,the sample with 1 wt% TAHP and 3 wt% TAD obtained an LOI value of 36.0% and passed the UL94 V-0 rating test.During combustion,TAHP/TAD system locked more phosphorus-containing components in residue and formed a phosphorus-rich char layer mixed with aluminum phosphate.The results confirmed that the interaction between TAHP and TAD formed the synergistic barrier effect during combustion.The barrier effect combined with gas-phase flame retardant effect of TAD caused the optimal flame retardancy in gaseous phase and condensed phase,which imposed better flame retardancy to epoxy thermosets.(3)TAHP was also applied into DGEBA cured by DDM with three reactive-type phosphaphenanthrene compounds,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO),10-(2,5-dihydroxyphenyl)-10-H-9-oxa-10-phosphaphenanthrene-10-oxide(ODOPB)and(1,1'-bis(4-hydroxyphenyl)-metheylene-bis(9,10-dihydro-9-oxa-10-phosphaphen-anthrene-10-oxide-2-hydroxypropan-1-yl)(DPOH),respectively.Their flame-retardant behaviors and the mechanisms were also investigated.Compared with TAHP/DOPO and TAHP/ODOPB system,TAHP/DPOH system simultaneously enhanced the LOI value and UL94 rating.During combustion process,2%TAHP/2%DPOH-EP/DDM and 1%TAHP/3%ODOPB-EP/DDM notably decreased the pk-HRR value and formed char layer with closed holes and aluminium phosphate particles.The Raman spectra tests further revealed that the residues of 2%TAHP/2%DPOH-EP/DDM and 1%TAHP/3%ODOPBEP/DDM possessed the char layer with higher graphitization degree,thereby imposing stronger barrier protection effect to residues.Accordingly,the char layer inhibited the burning intensity and enhanced the flame retardancy of epoxy thermosets.