Synthesis Of Phosphorus-containing Polymeric Flame Retardant And Its Flame Retardant Mechanism On Epoxy Resins

Majority of flame retardants used in materials are consisted of low-moleculer-weight chemicals.Once those chemicals escaped from the manufacturing process or leaching out of the product over years,they began to have environmental impact and do harm to health.With the advantage of environmental profile,polymeric flame retardants have been widely researched by manufacturers and researchers.To achieve high flame retardancy,several polymeric flame retardants containing phenylphosphate,PEPA-O-phosphoramide,phosphinic amide,phenylphosphonate and phenylphosphoramide were synthesized and well characterized.The relationships between the structure and thermal properties,flammability of the polymeric flame retardants were investigated.Then,the synthesized flame retardants were applied to epoxy resin to improve the flame retardancy.The influence of these flame retardants containing different structure on the flame retardancy,thermal properties,fracture toughness and flame retardant mechanisms was studied by various methods.The main work is composed of the following parts:(1)By changing original synthesis route of liquid bisphenol A bis(diphenyl phosphate),a simple and green method for the preparation of solid polymeric bisphenol A bis(diphenyl phosphate)(PBDP)is presented.PBDP is solid powder at room temperature with a T_g value of 57°C,suitable for transportation,storage and especially for application.With the addition of 20 wt.%of PBDP into EP,UL-94 V-0 rating was achieved and LOI values of flame retardant epoxy resin increased from 24.7%to 29.8%,meanwhile the glass transition temperature was maintained at the high level of the pure EP.Besides,a slight improvement in fracture toughness was observed in the EP/PBDP composites compared to the pure EP.The flame retardant mechanism of PBDP combines condensed phase and gas phase mechanisms such as the catalysis effect,char-forming effect,gas activity,and the improved thermal stability of char layer.(2)To reduce the smoke density during combustion,a novel polymeric intumescent flame retardant,poly(4,4'-diamino diphenyl sulfone 2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-methanol(PEPA)-substituted phosphoramide)(PSA),has been synthesized through solution polycondensation.PSA PSA had sufficient molecular weight,high T_gs and thermal stability,with a residual char of 66.3 wt.%at 700°C.The incorporation of PSA and its mixtures with ammonium polyphosphate(APP)could effectively enhance the flame retardancy and thermal stability of epoxy resins.With the addition of 5 wt.%cooperated with 5 wt.%APP,the LOI value of EP/PSA composites reached 32.0%and passed the UL94 V-0 rating.Differential scanning calorimetry(DSC)indicated that the incorporation of PSA and APP slightly increased the glass transition temperature of EP.Cone test,TGA data and TGA-FTIR analysis showed that the addition of PSA and APP greatly increased the amount of residual char and apparently reduced the amount of pyrolysis products during combustion.The thermal degradation kinetics results of the EP/PSA composites by Kissinger method showed that the incorporation of PSA could reduce the apparent activation energy,while incorporation of PSA and APP increased the apparent activation energy.(3)In order to further improve the flame retardancy,three polyphosphinic amides containing sulfonyl,methylene and ether group were synthesized through solution polycondensation and well characterized.Results showed that the polyphosphinic amides have high Tg,thermal stability and low flammability depending on the diamines incorporated.The thermal stability increases in the order methylene<ether<sulfonyl.(4)A comparative evaluation of the flame retardancy and thermal properties of epoxy resins containing the three polyphosphinic amides is presented.The addition of polyphosphinic amides could reduce the heat release rate and promote the formation of intumescent char layer.With the addition of 15 wt.%polyphosphinic amides,EP/POS and EP/POA could pass the UL-94 V-0 level,while EP/POM only achieve a UL-94 V-1 level,indicating the better flame retardancy of ether and sulfonyl group.However,it showed that the change of the three main chain group didn't influence the heat release of flame retardant EP.The flame retardancy and thermal properties of flame retardant EP only depended on the chemical structure of phosphorus atom.POS showed negligible negative effects on the Tg of flame retardant EP,while the Tg of EP/POM and EP/POA decreased within 10~20°C.It demonstrated that the incorporation of sulfonyl group into polymeric flame retardant could efficiently increase the Tg of epoxy resins.(5)Fourpolysulfonescontainingphenylphosphate,phosphinicamide,phenylphosphonate and phenylphosphoramide were successfully synthesized through melt polycondensation and solution polycondensation.The influence of the various phosphorus-containing groups on the thermal properties and flammability of polysulfones were investigated by TGA,DSC and MCC tests.The polysulfones all have high T_g and thermal stability depending on the structure of phosphorus-containing groups.The absence of phenylphosphine oxide,imino groups and sulfonyl group in one molecular could greatly increase the T_g of polymer.(6)To find the higher flame retardancy of structure,flame retardant epoxy resins containing four polysulfones(phosphorus content around 1.25 wt.%)is presented.The relationships between the structure and thermal stability,fire behavior were studied by TGA,DSC,CONE and MCC tests.The UL-94 vertical burning results illustrated that the flame retardancy of the EP composites increased in order of PDSPD?PBS(no rating)<PSPPP(V-1)<POS(V-0).The crosslinking char layer and lower apparent activation energy at high temperatures of EP/POS and EP/PSPPP composites demonstrated that the higher gas activity of P-C group in gas phase.And the P-O-C group could effectively promote the char forming process than P-C group,resulting in condensed char layer.Although there are great differences between the Tg and polysulfones,only slightly changes on the Tg of the flame retardant EP was observed,meaning that the strong molecular interaction between the polysulfones and EP.