Application of Vanillin-Derived Phosphorus-Containing Schiff Base/DOPO Compounding Flame Retardants in Epoxy Resins
A phosphorus-containing Schiff base flame retardant(PH-VAN-AP)was synthesized using phenylphosphoryl dichloride,vanillin,and 4-aminophenol as main raw materials,and its structure was proved to be as expected through FT-IR,1H-NMR and 31P-NMR.DOPO and PH-VAN-AP were incorporated into epoxy resin(EP)as compound flame retardant PH/DOPO,and their flame retardant properties were characterized by vertical burning(UL-94),limiting oxygen index(LOI)and cone calorimetry test(CCT),and the thermal stability,thermal degradation process of the epoxy resin were analyzed by thermogravimetric(TG)and differential thermal scanning calorimetry(DSC)and glass transition temperature(Tg).The experimental results show that PH/DOPO shows both gas-phase and condensed-phase flame retardant mechanisms,which can effectively improve the combustion performance of EP.Specifically,when only 3%of PH/DOPO was added to the system,it successfully passes the UL-94 test and reaches the V-0 rating,and its LOI increases from 24.7%to 34.8%.In addition,the peak heat release rate(PHRR)and total heat release(THR)are reduced by 257 kW/m2 and 8 MJ/m2,respectively,and the residual is improved by 6.8%.With the addition of 3%PH/DOPO,the Tg of the epoxy resin decreases from 149.5℃to 148.1℃with little change,indicating that PH-VAN-AP can improve the Tg decrease due to the addition of DOPO into EP to some extent.
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