Preparation Of Dynamically Covalently Cross-linked Vanillin-based Thermosetting Resin And Its Degradability Research

Traditional thermosetting resins are widely used in various fields of daily life due to their stable cross-linked network structure,but their recycling difficulties and non-reprocessing cause waste of resources and environmental pollution.As the second largest renewable resource,lignin has shown wide application prospects in the preparation of thermosetting materials.However,due to its poor solubility and non-uniformity of molecular structure,the types of raw materials that can be used to prepare lignin-based thermosetting resins are single,and the resin cross-linking structure is complicated and difficult to control.Vanillin is a biomass monomer obtained after the degradation of lignin.It contains both aldehyde groups and phenolic hydroxyl groups.It has strong structural controllability and is convenient for the structural design of thermosetting resins.At the same time,dynamic covalent bonds can combine the stability of classic covalent bonds with the reversibility of non-covalent bonds to solve the dilemma faced by traditional thermosetting materials.Therefore,this article introduces dynamic covalent bonds into vanillin-based thermosetting materials,To achieve its recycling and reuse,without causing environmental pollution,to achieve the requirements of sustainable development.The introduction of dynamic covalent bonds can also give polymer materials self-healing,thermoplastic processing,degradable recycling and other characteristics.In this paper,dynamic imine bonds are introduced into poly-Schiff base resins and epoxy resins,which give them the properties of degradable recovery and thermoplastic processing.At the same time,the preparation of epoxy resins based on dynamic enamine bonds is explored.The main content is divided into the following aspects:(1)A new vanillyl dialdehyde monomer containing dialdehyde group was prepared by using vanillin as a raw material,and a vanillin-based poly Schiff base resin was prepared by cross-linking diethylene triamine and tri(2-aminoethyl)amine..The research results show that the polyschiff base thermosetting resin can realize its thermoplastic processing at 150°C,and can realize its recycling and degradation under the acid solution of 50°C.The tensile strength and elongation at break did not decrease significantly after three times of hot processing,reaching 47.43±2.46 to 57.1±6.01 MPa and 16.34±2.86 to 13.01±1.51%,respectively,and can be self-healing within 180°C,2h.Moreover,it is thermally stable below300°C,and the glass transition temperature increases with the increase of the degree of crosslinking,from 48°C to 64°C.(2)A vanillin epoxy monomer containing an epoxy structure was prepared from vanillin,and the monoglycidyl structure of vanillin epoxy(Van-Ep)was cured with an isophorone diamine(IPDA)hardener.The original Van-Ep/IPDA has a tensile strength of about 65.0MPa at break.At 130°C and 10 MPa,it can be reprocessed by hot-pressing for 10 minutes.All reprocessed vanillin-based epoxy vitreous bodies show original mechanical properties.And this epoxy glass body can be degraded in acidic solution.The glass transition temperature(T_g)reaches 121°C,and all samples are thermally stable at a temperature of 222°C.(3)The feasibility of using epoxy enamine structure to prepare epoxy vitrimers was investigated,and the results showed that the enamine structure can be quickly prepared without catalyst at room temperature,and it does not react with epoxy;The reactivity is higher than that of epoxy and amine.Therefore the crosslinked structure of the enamine-based epoxy resin was determined.This laid the foundation for the preparation of reworkable epoxy vitrimers based on enamine bonds.