Study On High-performance Degradable Epoxy Resins Based On Vanillin

Due to epoxy resins'superior and tunable physical and mechanical properties,they have been widely used in coatings,adhesives,laminated circuit board,electronic component encapsulations and high-performance composites.However,more than 90%of epoxy resins are derived from bisphenol A,which has been shown to have negative impact on the environment and human endocrine system.Thus,it is vital to find some alternatives to bisphenol A.Meanwhile,the limited and rising prices of fossil resources,climate change from carbon dioxide emissions and other environmental issues have generated interest in bio-renewable materials with low prices and enhanced environmental benefits.Bio-based resources are likely to be used to prepare thermosetting materials with properties comparable to petroleum-based systems.However,the sustainable development of materials requires us not only to reduce the consumption of non-renewable resources,but also to recycle materials after use.To date,most thermosets are difficult to be reshaped or reworked by heating or solvent due to their irreversible covalent cross-linked network,making thermosetting materials difficult to be recycled.So far,the reported degradable thermosetting resins do not have satisfactory thermal and mechanical properties.Therefore,design of high-performance thermosetting materials with good recyclability is necessary.To address the above issues,the following works have been done:?1?A novel fully bio-based degradable diepoxy containing bicyclo diacetal?DGEVE?was synthesized from bio-derived vanillin,erythritol and epichlorohydrin by coupling of vanillin with erythritol followed by reacting with epichlorohydrin to introduce two epoxy groups,overcoming the issue of using petroleum-based raw materials for traditional epoxy resins.The chemical structures of the monomers were characterized by FTIR,¹H NMR,¹³C NMR,and XRD.Meanwhile,the degradation mechanism under acidic conditions was explored by real-time NMR,which laid a foundation for the degradation of epoxy resin.?2?The vanillin-based epoxy monomer was cured by DDS?diamino diphenyl sulfone?,for easy evaluation,bisphenol A epoxy monomer was also employed here as the control and cured with the same curing agent.The curing kinetics,thermal properties,mechanical properties as well as the degradation condition and mechanism were determined by FTIR,DSC,DMA,TGA,nanoindentation universal stretching machine and real-time NMR.The results show that the curing reactivities of the vanillin-based epoxy is lower than DGEBA.Meanwhile,due to the rigidity of the dicyclo diacetal structure,it showed high glass transition temperature of 184°C,good thermal stability(T_d5:308°C)and its modulus?4.7 GPa?and hardness?0.30 GPa?are even higher than those of bisphenol A epoxy resin.Due to the degradability of dicyclo diacetal structure in the epoxy resin,the cross-linked epoxy network could be readily decomposed?completely dissolved in1M HCl solution at 50°C within 40 min?.At the same time,vanillin-based epoxy resins have been studied under different degradation conditions such as temperature,type of acid,and type of organic solvent.As the temperature increased,the degradation rate gradually increased,and the temperature had a great influence on the degradation rate.It took 7 hours at 25°C but took noly 50°C for 84 min.For the degradation,organic solvent is necessary.When acetone/water?v/v?<5:5,the resin can only swell but not be degraded.The greater the polarity of the organic solvent,the higher the H⁺concentration in the solution and the faster the degradation rate.Besides,it can kept stable under neutral and basic conditions even during hot-humid aging test.Finally,through the real-time NMR technologies,the degradation of monomer VE and cured epoxy resin both followed first-order kinetics.