The Synthesis Of A Novel Phosphorus,Nitrogen And Sulfur-Containing Flame Retardant And Its Application In Epoxy Resins

Owing to its excellent adhesion performance,thermal stability,insulation and mechanical properties,epoxy resins(EP)are used widely in many fields such as civil construction,board sea-going ships,electronic and electrical etc.However,like most of polymers,the utilization in some fields which require high flame resistance is limited because of the flammability of epoxy resin.Therefore,it is necessary to incorporate flame retardants into epoxy resins.As the requirement of forbidding uing halogen grows and people are paying more attention to the environment,development of novel halogen-free flame retardants becomes a focus nowadays.Phosphorus-nitrogen-sulfur containing flame retardant displays the characteristic of high flame retardant efficiency,environment-friendly and smoke suppression,and it conforms to the future direction of non-halogen flame retardant.In this work,two phosphorus-nitrogen-sulfur containing reactive flame retardants were synthesized and used to prepare flame-retardant EP with satisfactory mechanical properties.The effects of flame retardants on the thermal,mechanical,flame-ratardant and curing properties of EP were investigated systematically,and possible thermal degradation mechanisms of flame-retardant EP were proposed.The detailed results of the main research in this work are summarized as follows:Firstly,two novel reactive flame retardants N,N'bis(2-thiazolyl)phenylphosphonic(PPNB)and N,N'bis(2-benzothiazolyl)phenylphosphonic(PPNDB)were synthesized via one-pot reaction.The structures and properties of products above were characterized and confirmed by a series of tests and analyses.Through the single factor experiment,we found the optimal reaction conditions of synthesis of flame retardants.Secondly,the effects of PPNB and PPNDB contents on the flame-retardant,thermal and mechanical properties of EP were investigated systematically.The results showed that the flame-retardant properties of PPNB/DDM-EP and PPNDB/DDM-EP curing systems were obviously improved compared to DDM-EP curing system.The thermal stability of PPNB-modified EP was better that of PPNDB-modified.Howerer,mechanical and flame-retardant properties of PPNDB-modified EP were better than that of PPNB-modified.Thirdly,the curing kinetics of PPNB/DDM-EP and PPNDB/DDM-EP epoxy systems were investigated and the curing parameters were analyzed It turned out to be that the incorporation of flame retardant could lower the apparent activation energy and improve the reaction rate constant.It could be seen that both of PPNB and PPNDB could accelerate the curing reaction simultaneously,but the effect of PPNB was more obvious.Finally,the possible retardant mechanisms of PPNB and PPNDB were investigated by analyzing the evolved gases and residue chars of PPNB/DDM-EP and PPNDB/DDM-EP epoxy systems.The conclusions could be drawn from the results that the flame retardant groups of PPNB and PPNDB,which simultaneously functioned in the gaseous and condensed phase,were responsible for the enhanced flame-retardant efficiency.The stronger condensed-phase flame retardation was for PPNB,whereas PPNDB tended to be a greater effect of gas-phase flame mechanism.