Synthesis Of Bioimine Hardener And Its Application In Epoxy Vitrimers Composites

This article investigates the application issues of epoxy resin in composite materials.Its application in some fields is limited due to its non-recyclable and flammable characteristics.Therefore,this article synthesized a curing agent containing imine bonds from bio-based vanillin and 4,4-diaminodiphenyl sulfone,and prepared a new type of epoxy vitrimer by adding flame-retardant epoxy resin,which can be used to make the cover of new energy vehicle battery box.As a result of the implementation of dynamic imine covalent bonds,the cured epoxy vitrimer can undergo reprocessing and degradation.According to the study,bio-based vanillin-cured epoxy resin exhibits comparable thermal,mechanical,and flame retardant properties to the commercially available epoxy resin(BAC 449)utilized in the production of battery box covers.what’s more,the epoxy vitrimer has the advantages of recyclability and degradability.Finally,the two types of epoxy resin were combined with glass fiber to prepare composite,and their flame retardancy both reach UL94-V0 level.The composite prepared from the epoxy vitrimer even exhibited better mechanical properties.And the glass fiber could be recycled without damage through the degradation of the epoxy vitrimer resin.This research holds immense importance in advancing the production of epoxy resin that is both flame-retardant and recyclable.The primary focus of this study includes:(1)A curing agent(VD)containing imine bonds was synthesized using bio-based vanillin and 4,4-diaminodiphenyl sulfone as raw materials.The chemical structure of VD was characterized by FTIR and ~1HNMR spectra.Then,the curing kinetics of the vitrimer resins DHU-VD and the traditional resin BAC 449 were studied using Kissinger and Isoconversional methods,and their apparent activation energies were calculated.Finally,based on the results of DSC testing,the curing conditions for both were determined to be135℃×2 h.(2)The thermal,mechanical,flame retardant,structural dynamics,and repeatable molding properties of DHU-VD and BAC 449 epoxy resins were further studies and compared.The results showed that the flame retardancy of both epoxy resins reached UL94-V0 level.The glass transition temperatures of DHU-VD and BAC 449 resins were148℃and 177℃,respectively.The initial thermal decomposition temperatures were 328℃and 336℃,respectively.The tensile strength was 56 MPa and 67 MPa,respectively.And the tensile modulus was 2652 MPa and 3269 MPa,respectively.The mechanical performance of the two resins was similar.Solvent resistance experiments showed that DHU-VD resin hadcross-linked network structure.In addition,due to the presence of dynamic imine bonds in the molecular structure,DHU-VD resin shows stress relaxation behavior due to the change of network structure at high temperature.The topological freezing transition temperature of the resin is 120℃,and the activation energy was 140 k J/mol.It could be reprocessed and the retention ratio of its tensile strength and tensile modulus could reach 75%and 96%,respectively.DHU-VD epoxy resin could be completely degraded by heating at 100℃for 5hours In the small molecule amines solvent.(3)DHU-VD and BAC 449 were used as matrix resins to prepare glass fiber reinforced composite materials(GFREPs)through the hand lay-up and hot press method.Both resins achieved UL94-V0 flame retardancy,and the GFRP made with DHU-VD resin showed superior mechanical performance.Additionally,the glass fibers in the GFREPs were recycled by degrading the resin matrix,There is no residual resin and no structural damage on the recovered glass fiber surface.