Studies On Synthesis And Performance Of Vanillin-based Recyclable Epoxy Resin

Bisphenol A glycidyl ether（DGEBA）is widely used in coatings,adhesives,composite materials,electronic packaging and other fields due to the excellent mechanical and thermal properties.However,with the problems of the non-renewability and the biological toxicity of bisphenol A,the preparation of epoxy resins from bio-based resources has attracted widespread attention.As a product of enzymatic hydrolysis of lignin,vanillin is very suitable for preparing epoxy resin due to its easy modification and rigid benzene ring.However,the epoxy resin has a three-dimensional network after cured,which makes it difficult to recycle or degrade,which caused waste of resources and environmental pollution to a certain degree.In response to the above problems,recyclable epoxy resins were prepared via chemical modification to introduce reversible covalent bond in its structure from bio-based vanillin,while the performances were compared to DGEBA.The research work is mainly divided into the following two parts:（1）An epoxy resin based on imine bond:A diphenol monomer contains diphenolic aldehyde groups was prepared by formaldehyde and vanillin,and epoxy groups were introduced through the reaction of phenolic hydroxyl groups and epichlorohydrin to prepare diphenol monomers difunctional epoxy resin which contained two aldehydes.The structure of the resin was characterized by Fourier infrared（FT-IR）and nuclear magnetic hydrogen/carbon spectroscopy(¹H-NMR/¹³C-NMR),then the resin and DGEBA were cured with polyetheramine D230 and infrared was used to prove that the resin was successfully cured.The physical mechanical and thermal properties,gel content,swelling degree,ductility,degradation performance and recyclability of the cured resin were studied.The results showed that the cured resin exhibited similar gel content and lower swelling degree to that of cured DGEBA,and the glass transition temperature,fracture stress,elongation at break,crosslink density and residual carbon content were all higher than those of cured DGEBA.The cured resin can be reprocessed and molded under the conditions of hot pressing at 150°C for10 minutes after shattering.The chemical structure showed not changed significantly was proved by infrared and thermal weight loss,and the performance of the reprocessed material was almost equivalent to that of the cured DGEBA.（2）An epoxy resins based on acetal bonds:A difunctional hydroxyl monomers that contains acetal ring was synthesized from vanillin and trimethylolpropane,then reacted with epichlorohydrin to prepare difunctional epoxy resin with acetal ring structure.The structure of the resin was characterized by Fourier infrared（FT-IR）and nuclear magnetic hydrogen/carbon spectroscopy(¹H-NMR/¹³C-NMR).Then the resin was cured with trimethylolpropane tris（3-mercaptopropionate）ester（TMP）,pentaerythritol tetra（3-mercaptopropionate）ester（PETMP）and 2,3-dithio（2-mercapto）-propane mercaptan（PETP）.Infrared was used to prove that the epoxy group and the sulfhydryl group had successfully reacted while the cured DGEBA with PETMP was used as a comparative sample.The physical mechanical and thermal properties,gel content,ductility,degradation performance and recyclability of the cured resins were studied.The results showed that the cured resin displayed a gel fraction close to 100%,a lower swelling rate（<10%）,a glass transition temperature equivalent to that of the cured DGEBA,and a higher elongation at break as well as carbon rate.The cured resin with TMP showing the stretch curve of the elastomer,while the cured resins with PETMP and PETP both show the stretch curve of toughness and fracture.The cured resin can be reprocessed and shaped by hot pressing at 160°C for 20 minutes.In addition,the cured resins also showed excellent acid degradability and can be degraded in acidic solutions of a variety of organic solvents.