| Epoxy resin is widely used in coatings industry and electronics industry depending on its excellent mechanical properties.Among them,the glycidylamine type epoxy resin has good bonding strength and mechanical strength,and which has been used for manufacturing composite materials at home and abroad and been used in aircraft and space equipments.However,epoxy resin may be affected inevitably by external factors such as impact during using.Consequently,damage inside the epoxy resins will be caused,and which will further affect the mechanical properties and service life of the epoxy resins.The scientific researchers have found a simple and effective,economical and environmentally friendly method to address this problem.Namely,the thermo-reversible Diels-Alder(DA)covalent bond is introduced into the epoxy resin.As a result,the epoxy resin is endowed with self-healing function.The method not only extends the service life of epoxy resin,but also saves resources and protects the environment.Moreover,the application scope of epoxy resin can be extended.On the other hand,thermoplastic polyurethane material is a kind of polymer material with high strength,good bonding property and soft molecular chains.It is widely used in daily life,industrial and agricultural production,medicine and other fields.The toughness of epoxy resin can be improved when thermoplastic polyurethane is introduced into epoxy resin.Consequently,the epoxy resin with both excellent strength and toughness can be obtained.In this dissertation,the self-healing epoxy resin was designed and synthesized based on Diels-Alder(DA)reaction.The thermal reversibility,self-healing behavior,and reprocessing property of resultant EP-DA were investigated in depth.Meanwhile,thermoplastic polyurethane was synthesized and introduced into the self-healing epoxy resin system.The self-healing behavior of thermoplastic polyurethane-modified epoxy resin was studied in detail.The main contents and results are as follows:(1)Preparation and properties of self-healing epoxy resin based on Diels-Alder reaction: The di-epoxy group-based N,N-diglycidyl-furfurlamine(DGFA)containing furan ring was synthesized via the reaction between epichlorohydrin and decylamine.Then a thermo-reversible epoxy resin(EP-DA)with self-healing performance was prepared by Diels-Alder(DA)reaction between the synthesized DGFA and bismaleimide(BMI).The chemical structure and thermal reversibility of resultant EP-DA were investigated by FT-IR and DSC.Results confirmed that the thermo-reversible DA bonds were generated in EP-DA successfully and has excellent thermal reversibility.In addition,the optimal reaction temperature and time of DA reaction were determined.Finally,results show that EP-DA has excellent mechanical properties and reprocessing ability.(2)Repair behavior and mechanism of self-healing epoxy resin based on Diels-Alder reaction: The repair behavior of self-healing epoxy resin was investigated by macroscopic observation and three-point bending test.The samples of EP-DA which was subjected to cracking by impact were heat-treated and it was found that the crack healing rate increased gradually with the increase of temperature and the prolongation of heat treatment time.In order to explore the multiple healing capabilities of self-healing epoxy resin,three-point bending test for repaired sample after multiple fracture-heat treatment were investigated.The results show that the first healing efficiency of the EP-DA can reach 71.65% while the healing efficiency after three cycles of destroy-repairs can still reach 54.49%.It shows that EP-DA has good multiple repair performance.The self-healing mechanism based on DA reversible reaction of self-healing epoxy resin was explored through the measurement of healing behavior and healing effect after analysis.(3)Preparation and properties of thermoplastic polyurethane-modified self-healing epoxy resin: The thermoplastic polyurethane(TPU)was synthesized through the extension of-NCO-terminated polyurethane prepolymer.Then TPU was introduced into self-healing epoxy resin and thermoplastic polyurethane-modified self-healing epoxy resin(EP-DA-TPU)was prepared.Result show that the DA bond is still generated in EP-DA-TPU through comparing of chemical structures of EP-DA and EP-DA-TPU and which is examined by FT-IR.EP-DA-TPU also has good thermal reversibility.After the impact test and three-point bending test of EP-DA-TPU samples with different TPU additions,it can be concluded that the toughness of self-healing epoxy resins has increased due to the introduction of thermoplastic polyurethanes.And the impact strength and bending displacement of EP-DA-TPU samples reach the maximum when the amount of TPU is added at 10 phr.(4)Repair behavior and mechanism of thermoplastic polyurethane modified self-repairing epoxy resin: The self-healing behavior of EP-DA-TPU with different thermoplastic polyurethane additions was observed,and it was found that the crack healing effect of EP-DA-TPU samples is enhanced while the rate of healing increased gradually with the increase of thermoplastic polyurethane amount.Multiple fracture-heat treatment tests were performed on self-healing epoxy resin with different amounts of thermoplastic polyurethane.Three-point bending test results show that the first self-healing efficiency of self-healing epoxy resin is improved obviously,and it can reach more than 80%.The self-healing efficiency still can reach more than 55% after three repairs.Results show that EP-DA-TPU has good multiple self-healing performance.The introduction of thermoplastic polyurethane greatly improves the repairing ability and repair efficiency of self-healing epoxy resin.By analyzing the healing behavior and healing effect of EP-DA-TPU,it is concluded that EP-DA-TPU has the synergistic healing mechanism.I.e.,of the cracks in EP-DA-TPU are repaired by both the movement of thermoplastic polyurethane chains and thermo-reversible DA reaction. |
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