Preparation And Flame Retardant Mechanisms Of Flame Retardant Curing Agent Epoxy Resin Composites Containing Phosphorus

Epoxy resin is among the most useful of thermoset materials,and shows advantageous properties such as: good chemical stability,low shrinkage on cure,high adhesion to many substrates,remarkable electrical properties,excellent mechanical properties,tensile strength and good workability.Therefore,epoxy resins are widely used as coatings,electrical and electronic,casting materials in the dustries and adhesive.However,the LOI of conventional epoxy resins is 19.8%,which limit their application for safety consideration,and development of flame retardant epoxy resins into the research of the important goals of the epoxy resin composite materials.Halogen-nitrogen containing was widely used to suppress the flammability of EP.However,flame-retardant epoxy resins containing halogen could produce poisonous and corrosive gases.Therefore,halogen-free compounds have attracted attention.Especially the phosphorus-nitrogen containing compounds mainly act as intumescent flame retardants which produce less toxic gas and smoke.The research work of this dissertation is mainly involving the synthesis and thermal degradation mechanism about the phosphorouscontaining epoxy resins.A novel curing and flame-retarding agent(PEPA-TMA),has been synthesized via reaction of 2,6,7-trioxa-l-phosphabicyclo-[2.2.2]-octane-4-methanol(PEPA)with trimellitic anhydride(TMA).The combination of a novel flame retardant curing agent containing a caged bicyclic phosphate structure and the anhydride group into the same compound.The reaction conditions and time of the reaction were determined by several experiments.Chemical structure of the material was characterized with FTIR,1H-NMR spectra and 31P-NMR spectra.The results showed that the final product was 81.65 g,and the yield was 72%.PEPA-TMA and melamine cyanurate(MCA)were combined into epoxy resin(EP)to obtain halogen-free flame retardant epoxy resin composites.Flame retardancy of EP/PEPATMA/MCA was investigated by limited oxygen index(LOI)and UL-94 vertical burning test.The thermal decomposition of EP/PEPA-TMA/MCA was investigated by TGA analysis.The glass transition temperature was investigated by dynamic mechanical analysis(DMA)test.HRR?THR?SPR and TSP was investigated by CONE test.Morphology of char combustion of EP composite was observed by SEM.The results showed that the most effective amount of phosphorus is 2.5 wt% and the best ratio of PEPA-TMA and TMA is 2:1.The thermal degradation and charring process of EP composites were characterized using TGA-FTIR?SEM and EDX.Moreover,the synergistic effect between PEPA-TMA and MCA is coordinated by gas phase and condensed phase flame retardant mechanisms.The formed volatilized products on thermal degradation of flame retarded epoxy resin(EP)systems indicated that the volatilized products are mainly phosphine(PH3),carbon dioxide(CO2),water(H2O)and aromatic compounds.The flame retarded mechanism was studied by TGAFTIR and Energy-dispersive X-ray spectroscopy(EDS)coupled with the analysis of the char residues.In brief,it is speculated that the flame retardancy of PEPA-TMA in EP composite is the combination of gas phase and condensed phase flame retardant mechanisms.The consequence was that more P content will be available for flame retardant and char formation for EP composites.SEM observed that the increase of char residue can greatly hamper the transfer of heat and oxygen in the combustion layer and matrix,thus leading to flame retardant in condensed phase.Moreover,MCA released inert gases such as NH3 during the flame process.These inert gases diluted the flammability gases such as oxygen from combustion,thus leading to flame retardant in gas phase,had a synergistic effect of flame retardant for EP composites.