Study On Preparation And Properties Of Bio-based Epoxy Vitrimer Materials

As a thermosetting resin material,epoxy resin has good thermosetting,corrosion resistance and technology property.It is widely used in industrial fields such as coatings,castable,adhesives,and grinding materials.However,epoxy resin also has some shortcomings such as being difficult to recycle,not easy to degrade and not reusable,which goes against the green concept of material recycling.The epoxy vitrimer material is prepared by introducing dynamic covalent bond into the three-dimensional cross-linking network of the epoxy resin curing system.Under certain conditions,its three-dimensional network can be rearranged,so that the epoxy resin has repairable and reprocessing properties,which provides an optional exploration way for the reuse of epoxy resin curing materials.In this paper,a bio-based epoxy vitrimer material was prepared by introducing a variety of dynamic covalent bonds into the curing crosslinking network of epoxy resin using the hydrolyzed product of cellulose as curing agent.The material can be self-repaired,degradable and reused under the action of catalyst and heat.Specific research contents and conclusions are as follows:First,cellulose was hydrolyzed to polysaccharide at high temperature under the catalysis of acid.The effects of anhydrous ethanol content,hydrolysis temperature,catalyst content,hydrolysis time and other technological conditions on the degree of cellulose hydrolysis and hydrolysis products were investigated.The physical and chemical properties of the hydrolysates were characterized by cone-plate viscosity,gel permeation chromatography,high performance ion chromatography and infrared spectroscopy.The optimum conditions for cellulose hydrolysis were determined to be 160℃alcohol hydrolysis temperature,3%phosphoric acid content,1:2:1 mass ratio of cellulose,anhydrous ethanol and deionized water,and 3 h hydrolysis time.The hydrolysate obtained under this process condition is composed of two parts,in which the monosaccharide content accounts for 60%（the monosaccharide composition was composed of fucose content accounts for 31.2%,mannose content accounts for 22.8%,the content of glucose accounted for 21.7%and the content of glucose accounted for 24.3%）,the content of cellulose disaccharide accounted for 16.4%,the content of cellulose triose accounted for 9.8%and the content of cellulose tetracose accounted for 13.1%,and the remaining 0.7%was composed of some ash impurities.Secondly,the concentration of hydroxyl group and aldehyde group in the mixed polysaccharide was determined by infrared spectroscopy,and the concentration of hydroxyl group and aldehyde group were determined by microtitrator as 7.266×10^-3 mol/g and 1.252×10^-4 mol/g.Taking the hydroxyl group of the mixed polysaccharide as the active point,the mixed polysaccharide was prepared as polycarboxyl acid curing agent of epoxy resin by reacting with maleic anhydride.The mixed polysaccharide modified by maleic anhydride was further copolymerized with polycarboxylic acid to become the superbranched polycarboxylic curing agent of epoxy resin.Using the aldehyde group of the mixed polysaccharide as the active point,the mixed polysaccharide was prepared as the polyimine curing agent of epoxy resin by reacting with polyether amine.Polycarboxyl curing agent can be used to construct transesterification reversible covalent bond system of epoxy resin curing network,and imine curing agent can be used to construct imine reversible covalent bond system.Then,using zinc acetate or zinc acetylacetone as catalyst and polycarboxyl modified or polyimide modified mixed polysaccharide as curing agent,bisphenol A epoxy resin was prepared into a variety of different types of biomass epoxy vitrimer materials.Through TG analysis,thermal expansion analysis,dynamic mechanical analysis and mechanical performance test,the influences of different catalysts on topological transition temperature（T_v）,thermal stability and mechanical properties of biomass epoxy vitrimer materials were explored.Finally,it was determined that the vitrimer material prepared by zinc acetyl acetone catalyst has lower topological transition temperature T_v,lower glass transition temperature T_g,higher thermal stability and better mechanical properties.With acetylacetone zinc as catalyst preparation of double dynamic covalent bond vitrimer（DC-Z（Ⅱ）A）with the slightly lower gel content,slightly higher swelling rate,the most excellent thermodynamic properties and mechanical properties(σ_max=42.2 MPa andε_b=60%).The lowest glass transition temperature（T_g=62℃）and the lowest topological transition temperature（T_v=78℃）were obtained.Finally,the vitrimer properties of different modified biomass cured epoxy resin systems were studied.Containing imide exchange and ester exchange double dynamic covalent bond vitrimer material（DC-Z（Ⅱ）A）has A stronger ability of self-healing（under 150℃for 20 min 23μm crack was repaired）,excellent processing performance again（150℃hot press,90 min can be remolded and still maintained excellent mechanical properties）,excellent biodegradability（98%degraded for 10 h）and good solvent resistance.The composite material with DC-Z（Ⅱ）A as matrix and carbon cloth as reinforcement has good recyclability and excellent regeneration performance.