Study On High-performance Flame Retardant Epoxy Resins Based On Vanillin

Epoxy resin is one of the three general-purpose thermosetting resins,and has been widely used in coatings,adhesives,electronic packaging,composites,and other fields.However,more than 90%of the market share of epoxy resins are bisphenol A epoxy resin(DGEBA).Bisphenol A is fully dependent on fossil resources,and is a reprotoxic compound.Therefore,it is significance to develop synthetic bio-based epoxy resins with sustainable and abundant raw materials.Flamability is the common problem for epoxy resin even for the most polymer materials.Because the traditional halogen-containing and other flame retardant systems seriously endanger the environment and human health,their application has been greatly limited,the development of an applicable green or halogen-free flame retardant has gained much more attention.To address the above issues,the following works have been done:(1)Two flame retardant epoxy resins EP1 and EP2 were synthesized from lignin derivative vanillin and green phosphorus compound diethyl phosphite.The two epoxy resins were synthesized by one-pot reaction containing Schiff base formation and phosphorus-hydrogen addition between vanillin,diamines,and diethyl phosphite,followed by reacting with epichlorohydrin,which is relatively green compared with the synthetic routes of the reported vanillin-based epoxy resins using toxic compounds such as oxidant and reducer.(2)The two vanillin-based epoxy monomerswere cured by DDM(4,4-diaminodiphenylmethane),and DGEBA was used as the control.The curing kinetics,thermal properties,mechanical properties as well as the flame retardancyand flame retarding mechanism of epoxy systems were determined by DSC,DMA,TGA,tensile test,vertical burning test,limited oxygen index measurement,SEM,ICP,and XPS.Results showed that the curing reactivities of the two vanillin-based epoxies are similar to DGEBA.After curing they showed excellent flame retardancy with UL-94V0 rating and high LOI of?32.8%,which was due to the outstanding intumescent and dense char formation ability.More interestingly,there were no black smoke during the burning test for these two epoxy resins,but a lot of black smoke formed during the burning test for DGEBA.Meanwhile,it was found that the cured vanillin-based epoxies had exceedingly high T_gs of?214°C,tensile strength of?80.3 MPa,and tensile modulus of?2709 MPa,much higher than the cured DGEBA with T_g of 166°C,tensile strength of 76.4 MPa,and tensile modulus of 1893 MPa;and the properties of vanillin-based epoxies are easy to be regulated by using different“coupling”agents-diamines-during the synthesis process.(3)The vanillin-based epoxy monomer EP1 was used as an additive flame retardant together with ammonium polyphosphate(APP)to improve the fire resistance of DGEBA.The effects of the the ratio of EP1 and APP on theflame retardancyand thermal properties of DGEBA system were investigated by vertical burning test,limited oxygen index measurement,and TGA and DSC.Results showed that for the DGEBA systems with 10phr EP1 and APP,when the ratio of EP1 and APP was 3:7,2:8 and 1:9,the epoxy system could reach the UL-94 V0rating.Meanwhile,the glass transition temperature of the DGEBA systems increased with the increase of EP1 content,and the flame retardant DGEBA systems with EP1 and APP showed comparable even higher glass transition temperature than the neat DGEBA system.