Structure Design And Properities Of DGEBF Epoxy Network With Flexible Dangling Chains

Epoxy resins are versatile materials.Owing to their excellent mechanical property,high adhesion property,dimensional stability and thermostability,epoxy resins,usually employed as adhesive cements,coatings and matrix resins of the composite materials,are widely used in various industry fields.What’s more,through the selection of curing agents and design of formulations,they can meet the needs of different properties.However,the crosslink network of epoxy resins cured by curing agents is endowed with high crosslink destiny and high rigidness which show the defect of brittleness.In order to improve the application of epoxy resins in advanced technical field,researchers are devoting themselves to the design and perfect the toughening methods.But,there are some defects with traditional toughening methods,which can increase the viscosity of systems and induce the sacrifice of thermal properties,and it is very difficult to realize the improvement of modulus and toughness,simultaneously.In this thesis,we design cured network with flexible dangling chains,based on DGEBF and HHPA systems.Because the flexible chains are incompatible with rigid backbone of benzene ring,they could self-organize to the dispersed phases in different shape,size and distribution.The network structure and properties of modified material are investigated.Firstly,the epoxy networks with different dangling chains were prepared by the curing reaction of mixture(DGEBF,the monofunctional epoxy and the anhydride).The microstructures of phase separation were observed by the AFM and regulated by changing the content of dangling chains.The phase separation was also investigated by XRD.The morphologies of SEM imply the occurrence of ductile fracture when the modified materials were destroyed.The thermomechanical property of material was changed by addition of the flexible dangling chains.Its storage modulus is higher than that of unmodified system at room temperature.The thermal property of material declined with the introduction of flexible dangling chains and the tendency is serious with the increasement of addition.The tensile testing implies that the modified material(E0)is endowed with excellent mechanical property.The E4-20(molar ratio of epoxy group between BGE and DGEBF was 1:20)system shows a tensile strength of 98.5MPa,a modulus of 3.1GPa,an elongation of 6.1%and impact strength of 22.5kJ/m2,and increase 58.1%,6.8%,125%and 55.2%compared with E0 system respectively.The nano-sized and submicron-sized phase structure coexisted is found to be the most effective toughening method.After that,two prepolymers shaped with comb were prepared through anionic polymerization between epoxy and anhydride,and they were introduced into the cured network through the reaction of terminal functional group.FT-IR and GPC were used to characterize the prepolymers.Besides,AFM,SEM,XRD,DMA,DSC and tensile testing were used to study the microstructures of phase separations,crystallinity,thermal property,the thermomechanical property and mechanical property of cured material.The tensile fracture surface showed that there two different toughening mechanism induced by two different prepolymers.The effect of the different prepolymers toughening epoxy resins was compared to found that mechanical property of modified material was improved to a tensile strength of 101.8 MPa,a modulus of 3.1GPa,an elongation of 5.6%,and increase 63.4%,6.8%and 107%compared with E0 system respectively.