Synthesis Of Organic Phosphinate Salt With High Phosphorus Content And Study On Flame-retardant Properties

Alkylphosphinic acid metal salts are recently developed environmental friendly flame retardants,and they show excellent flame-retardant in epoxy and polyester.The flame retardant efficiency of alkyphosphinic salts increases as phosphorus content increases.In this research,a new type of flame retardant Aluminum mono-methylphosphinate in alkylphosphinate(MeP-Al)with a phosphorus content of 35.2%is designed according to structure-activity relationship and synthesized by three-step methods using methyl dichlorophosphine as starting material.The structure of MeP-Al is characterized with FTIR,~1HNMR,~1PNMR and XRF,the thermal properties of MeP-Al is analyzed by thermo-gravimetric analysis(TGA),and the solubility of MeP-Al in water is tested.MeP-Al is used as a flame retardant for epoxy resin(EP)and polyurethane elastomer(PU).The flame retardant performance and flame retardant mechanism of the composite material are discussed in detail.In EP/MeP-Al composite materials,20%mass fraction of MeP-Al into EP increases the LOI from 19.6%to 29.6%,making the flammability of the composite V-0.Me P-Al does not affect the curing process of EP,but affects the decomposition of the material after curing.At the initial stage(<10%weight loss),MeP-Al promotes the decomposition of EP,which delays the thermogravimetric loss of EP and significantly increased the carbon content of the material.The micro calorimeter instrument(MCC)analysis shows that MeP-Al can effectively reduce the rate of heat releasing and the amount of heat released.In EP system,adding 20%mass fraction of MeP-Al grants EP smaller value of Peak Heat Release Rate(PHRR)and Total Heat Release(THR)than Pure EP.Moreover,the thermal decomposition process is analyzed in detail by FTIR,and residual solid phase component is analyzed by FTIR and scanning electron microscopy(SEM)-spectrometer(SEM-EDS).Using FTIR,thermo-gravimetric-gas chromatography mass spectrometry(TG-GC-MS)and Py-GC/MS,gas phase composition of pyrolysis is analyzed.Then the pyrolysis model of MeP-Al and MeP-Al/EP is established.The results showed that flame retardant MeP-Al acts in gas phase and the condensed phase during combustion.In PU system,adding different mass fraction of Me P-Al to PU forms the composite materials(PU/MeP-Al).The flammability and performance under forced-flaming conditions are investigated.20 wt%of MeP-Al incorporate in PU achieves a V-0 classification in the UL 94 test.The MCC test shows that the total and the maximum heat release of composite(PU/MeP-Al)decrease sharply compare with pure PU.Glass-transition temperature declines when MeP-Al is added into the PU by DSC test.The influence of phosphorus compounds on the PU decomposition pathways is characterized using thermal analysis(TG)and evolved gas analysis(TG-FTIR).EDS is used to perform elemental analysis(aluminum and phosphorus)to the fire residue,and the morphology features of carbon residue layer is analyzed by SEM and digital camera.The results show that MeP-Al acts as condensed phase during combustion.