Synthesis,Curing And Properties Of Bio-epoxy Resin Based On Resveratrol And Carbon Fiber Composites

Carbon fiber reinforced polymer(CFRP),a kind of advanced composite material with high specific strength and high specific modulus,is widely used in aerospace,building reinforcement,transportation,and medical devices due to its superior resistance to high and low temperature performance,corrosion resistance,electrical conductivity,thermal conductivity,excellent X-ray transmission and biocompatibility.As a matrix resin for high-tech-field CFRP,epoxy is considered to be the best choice since its excellent mechanical properties,chemical resistance,electrical insulation and adhesion properties and dimensional stability.However,despite its extensive application,bisphenol A epoxy resin has been forbidden to use in food and human-touch fields in many regions such us medical devices due to its great threat to human health caused by the synthetic monomer bisphenol A.Therefore,it is highly desired to develop non-toxic alternatives to bisphenol A for application in epoxy resin.Along with people’s increasing awareness of environmental protection and the volatility of petroleum’s price,bio-based epoxy resins have attracted great attention in current research.In recent years,bio-based epoxy resins have been widely investigated to compound with carbon fibers due to their environmentally friendly,renewable,non-exhausting,widely sourced,and reserves abundant characteristics.However,it is quite difficult to balance the mechanical properties,thermal stability,and processability of different types of bio-based epoxy resins limited by their raw materials and molecular structures.Therefore,it is of great significance to develop nontoxic,environmentally friendly resins with good mechanical properties and thermal stability.On the other hand,the fluidity of the resins should meet the needs of practical applications for composite materials.Moreover,the rapid solidification of the resin at low temperatures is an important development trend.Consequently,it is an urgent issue to develop bio-based resins with moderate viscosity and lower activation energy for easy process and rapid curing without losing the mechanical properties of the composite materials.Based on this,resveratrol,a bio-based polyphenol compound with trans-stilbene structure was utilized for the synthesis of epoxy resin(TGER).The curing process was further illustrated by studying its curing mechanism.CF/TGER composite was prepared,and the effects of the viscosity of the resin system on the properties of the composite were studied in details.Finally,from the interface-design point of view,the surface functionalization of the carbon fiber was improved leading to higher interfacial shear and mechanical properties of CF/TGER composites.The main content of the thesis is as follows:(1)From the molecular-design point of view,a novel bio-based epoxy resin was prepared using resveratrol as a precursor.A series of characterizations of the properties of the resin matrix were conducted.Non-isothermal DSC method was applied to determine the process conditions of TGER/DDM,TGER/DDS and TGER/Me THPA.Mechanical properties and thermal stability of the respective curing systems were studied by nanoindentation and thermogravimetric analysis.Accordingly,a novel bio-based epoxy resin with high epoxy number,narrow molecular weight distribution and lower viscosity has been obtained.TGER/DDM,TGER/DDS,and TGER/Me THPA polymers have high rigidity and heatstability,with decomposition temperatures higher than 270 ℃ for all of the three systems.(2)Kinetic study of the curing process of the TGER/DDM system was performed via non-isothermal and isothermal DSC methods in combination with infrared spectroscopy.The activation energy of the curing reaction was figured out to be 59.32 k J/mol by non-isothermal DSC study.The Kininger equation was adopted to calculate the curing kinetic parameters of the TGER/DDM system.The Kamal autocatalytic model was proved to better describe the curing kinetics of the TGER/DDM system.The dynamic mechanical properties,mechanical properties,and thermal stabilities of TGER/DGEBA blended polymers were tested,and the Mc value of TGER/DDM is was calculated to be 851 g/mol,which is higher than the crosslink density of DGEBA/DDM,leading to higher storage modulus at room temperature.Along with Tg of 148 ± 0.8 ℃,great thermal stability and mechanical properties could be expected.(3)CF/TGER series composites were prepared by VARI molding process.The effects of curing agents DDM and DEDDM on the viscosity of the resin system and the performance of the composites were studied.The optimum ratio of the diluent BGE and its effect on the properties CF/TGER composites were also studied.The system viscosity test showed that the addition of DEDDM reduced the viscosity of the system,which was only 0.8 Pa.s at 25 ℃.The TGER/DEDDM had a longer pot life at medium and high temperature curing conditions.The gel time of the resin mixing system decreased with the increase of TGER content.CF/TGER/DDM and CF/TGER/DEDDM have excellent mechanical properties and thermal stability.With TGER/DDM as the matrix,the viscosity of TGER decreases with higher content of BGE,and the pot life of the resin systembecomes longer.The composite showed the best flexural strength(649 MPa)and tensile strength(559 MPa)with 15% of BGE.Thermal decomposition temperature of CF/TGER increases first and then decreases with rising BGE content.(4)Maintenance of the original tensile properties of carbon fiber and enhancement of the interfacial adhesion properties of CF and TGER substrates were achieved synchronously via CF modification by the graft of in-situ IA-EDA polymer.The in situ polymerized IA-EDA was demonstrated to be successfully grafted onto the surface of CFs of by XPS and FT-IR characterization.Scanning electron microscopy(SEM)images showed that the surface of CF was covered uniformly by the protective layer of the itaconic acid,leading to significantly enhanced surface roughness.The tensile strength of CF was increased by 5.0% based on single fiber tensile strength test.Depending on the test results of interfacial shear strength(IFSS)and mechanical properties between CF and TGER,the IFSS of CF-IA-EDA composite(46.7 MPa)is significantly improved by 44.6% compared to the original CF(38.1 MPa)composite.Meanwhile,the mechanical properties of functionalized CF/EP composites were also improved significantly: the flexural strength of the CF/TGER composite was increased by 18.5% after the treatment of CF.the Flexural modulus also increased significantly,along with the improvement of tensile strength(506.3 MPa)and Young’s modulus(22% higher).