Preparation And Properties Of DOPO-Based Intrinsic Flame-retardant Epoxy Resin Systems

Epoxy resins have been widely applied in electrical,electronic,engineering,building and other fields due to their outstanding adhesive property,dimensional stability,mechanical performance,electrical property and so on.As typical thermosetting resins,most of epoxy resins are highly flammable,which restricts their application in many fields.Hence,developing flame-retardant epoxy resins contributes to broadening the application of epoxy resins and then promoting the development of epoxy resins.In view of the trend of environmental protection,many halogen-containing flame retardants have been banned because they decompose to release toxic substances during combustion,and then halogen-free and low-toxicity DOPO-based flame retardants have become the focus of research field about flame retardants for epoxy resins.In order to improve the flame-retardant efficiency of DOPO-based flame retardants and reduce their adverse impact on the other properties of epoxy resins,a series of intrinsic flame retardants which contained phosphaphenanthrene and different nitrogen-containing flame-retardant groups were synthesized in this work.In addition,intrinsic flame-retardant epoxy resin systems containing phosphorus and nitrogen were prepared.The curing temperature,thermal stability and flame retardancy of the intrinsic flame-retardant epoxy resin systems were investigated by different tests.The gaseous-phase and condensed-phase flame-retardant effects of different flame-retardant groups in the intrinsic flame retardants were also discussed.The main points of this thesis were as follows:?1?A novel intrinsic flame retardant?BPD?containing phosphaphenanthrene and benzothiazole was successfully synthesized by one-pot reaction.BPD was used as co-curing agent of 4,4'-diaminodiphenyl methane?DDM?to prepare intrinsic flame-retardant epoxy?EP/DDM/BPD?systems containing phosphorus and nitrogen.The curing temperature,thermal stability and flame retardancy of EP/DDM/BPD systems were studied by DSC,TGA,LOI,UL94 and cone calorimeter tests.The flame-retardant effects of phosphaphenanthrene and benzothiazole groups in BPD were detected by TGA-FTIR,Py-GC/MS,FTIR and SEM-EDX.The result indicated that BPD was able to cure epoxy resin.The introduction of BPD led to the reduction of T_g and T_5%of EP/DDM/BPD thermosets and the increase of char yield at high temperature.BPD endowed epoxy thermoset with excellent flame retardancy.The LOI and UL94 rating of EP/DDM/BPD-1.0 thermoset which contained only 1.0 wt%phosphorus reached 39.1%and V-0,respectively.The av-HRR and THR of EP/DDM/BPD-1.0 thermoset were decreased by 35.8%and 36.5%compared with those of EP/DDM thermoset in the cone calorimeter measurement.Phosphaphenanthrene and benzothiazole groups in BPD worked together in the gaseous phase and condensed phase,which exerted the quenching effect and diluting effect in the gaseous phase and the blocking effect in the condensed phase.?2?A novel phosphaphenanthrene-containing and piperidine-containing intrinsic flame retardant?DPT?was successfully synthesized by a simple one-pot method and used as co-curing agent of DDM to prepare intrinsic flame-retardant epoxy?EP/DDM/DPT?systems which contained phosphaphenanthrene and piperidine groups.The results showed that DPT was also able to cure epoxy resin.The introduction of DPT resulted in the decrease in the T_g of EP/DDM/DPT thermosets but the largest decline was only 12°C.Meanwhile,the T_5%of EP/DDM/DPT thermosets was lower than that of EP/DDM thermoset,but the char yield at high temperature was higher than that of EP/DDM thermoset.The flame retardancy of EP/DDM/DPT-4 thermoset with 1.0 wt%phosphorus was significantly better than that of EP/DDM thermoset and that of EP/DDM/DOPO thermoset with the same content of phosphorus.The LOI and UL94 rating of EP/DDM/DPT-4 thermoset reached 38.3%and V-0,respectively.The pk-HRR,av-HRR,and THR of EP/DDM/DPT-4 thermoset were decreased by 38.8%,32.1%and 36.4%,respectively,in comparison to those of EP/DDM thermoset.Phosphaphenanthrene and piperidine groups in DPT synergistically promoted the formation of continuous and intumescent charred layers to inhibit the exchange of heat and oxygen.In addition,phosphaphenanthrene and piperidine groups also exerted the quenching effect and diluting effect in the gaseous phase to reduce the burning degree of volatile gases.?3?A novel intrinsic flame retardant?PHTD?containing phosphaphenanthrene and piperidine groups was successfully synthesized by a simple one-pot method.PHTD cooperated with 1,3,5-triglycidyl isocyanurate?TGIC?to prepare intrinsic flame-retardant epoxy systems containing phosphorus and nitrogen.The results showed that the active hydrogen in PHTD was able to react with the epoxy group in TGIC.The introduction of PHTD and TGIC had little effect on the T_g of the flame-retardant epoxy systems,and significantly improved the flame retardancy and char yields of the flame-retardant epoxy systems at high temperature.The LOI and UL94 rating of the flame-retardant epoxy system with 1.0 wt%phosphorus reached39.2%and V-0,respectively.And its pk-HRR,av-HRR and THR were only 47.5%,64.4%and 63.6%of those of the neat epoxy system.All these results indicated that the introduction of PHTD and TGIC greatly improved the flame retardancy of epoxy system.The significant improvement of flame retardancy of epoxy systems was mainly due to the phosphorus-nitrogen synergistic flame-retardant effect between phosphaphenanthrene,piperidine and triazine-trione groups in the condensed phase and gaseous phase.?4?Benzimidazole was selected as a novel nitrogen-based flame-retardant group,and a novel intrinsic phosphaphenanthrene-and benzimidazole-containing flame retardant?DTA?was successfully synthesized.DTA served as the co-curing agent of4,4'-diamino-diphenyl sulfone?DDS?to prepare the intrinsic flame-retardant epoxy?EP/DDS/DTA?systems.The results showed that the introduction of DTA had little effect on the curing temperature of epoxy systems.In addition,the introduction of DTA reduced the Tg and T5%of EP/DDS/DTA systems,but significantly increased the char yields at high temperature.The LOI and UL94 rating of EP/DDS/DTA systems were up to 39.6%and V-0.The pk-HRR,av-HRR,THR and av-EHC of EP/DDS/DTA-1.0 system with 1.0 wt%phosphorus were 56.6%,31.6%,34.4%and 40.5%lower than those of EP/DDS system.Moreover,the char yield at 500 s of EP/DDS/DTA-1.0 system was increased by 134.6%compared with that of the neat EP system.DTA greatly improved the flame retardancy of EP system and exerted the synergistic flame retardant effect in the gaseous phase and condensed phase.Phosphaphenanthrene and benzimidazole groups synergistically promoted the epoxy matrix to form continuous and intumescent char layers,and release PO radicals with quenching effect and nitrogen-containing inert gases with diluting effect,and then inhibited the sustained combustion of epoxy thermoset.?5?A novel intrinsic flame retardant?DIB?with imidazole and phosphaphenanthrene groups was successfully synthesized.DIB served as the co-curing agent of DDS to prepare the intrinsic flame retardant epoxy?EP/DDS/DIB?systems which contained phosphorus and nitrogen.Because of the catalytic effect of imidazole ring,the curing temperature of EP/DDS/DIB systems were lower than that of EP/DDS system.In addition,the Tg and T5%of EP/DDS/DIB systems were lower than those of EP/DDS system.However,the char yield at high temperature of EP/DDS/DIB systems was higher than that of EP/DDS system.The flame retardancy of EP/DDS/DIB systems was greatly improved by the introduction of DIB due to the phosphorus-nitrogen synergistic flame-retardant effect between imidazole and phosphaphenanthrene groups.The LOI and UL94 rating of EP/DDS/DIB-1.0thermoset with 1.0 wt%phosphorus reached 38.5%and V-0,and its pk-HRR,av-HRR,THR and av-EHC were decreased by 57.2%,37.9%,36.0%and 35.1%,respectively,compared with those of EP/DDS thermoset.Meanwhile,the char yield at500 s of EP/DDS/DIB-1.0 thermoset was improved by 115.4%in comparison to that of EP/DDS thermoset.During combustion,imidazole and phosphaphenanthrene groups synergistically promoted the epoxy matrix to form continuous and intumescent charred layers to exert the condensed-phase flame-retardant effect.In addition,both of them reduced the combustion degree of combustible gases and exerted the gaseous-phase flame-retardant effect.