| Epoxy resin has been widely used as coatings,adhesives,sealants and structural material because of its excellent mechanical property.Micro-cracks may be generated in epoxy resins when suffered from external factors.These cracks are difficult to detect and repair by instrument.Consequently,properties of epoxy resins can be reduced owing to accumulative micro-cracks.Inspired by the self-healing phenomenon of organism,scientists have developed a series of polymers and composite materials with self-healing property by imitating the self-healing mechanism of organism.It is an effective method of introducing the thermo-reversible Diels-Alder(DA)bonds into polymer to prepare self-healing materials.DA reaction has many advantages,such as low price and easily obtained raw materials,mild reaction condition,minimal side reactions and no metal catalyst is needed.In addition,the thermo-reversible DA reaction has high self-healing efficiency and multiple self-healing property.In this dissertation,self-healing epoxy resin(EP-DA)is designed and synthesized based on Diels-Alder(DA)reaction.The thermal property,thermal reversibility,self-healing behavior,and self-healing mechanism of resultant EP-DA are investigated in depth.Meanwhile,nitrile rubber(NBR)on self-healing behavior of EP-DA is investigated.The main contents and results are as follows:(1)Preparation and properties of self-healing epoxy resin based on Diels-Alder reaction: To produce a kind of self-healing epoxy resin based on Diels-Alder(DA)reaction(EP-DA),furfuryl glycidyl ether(FGE)is synthesized firstly via the reaction between epichlorohydrin and furfuryl alcohol.Next,EP-DA is prepared by the polymerization of FGE as well as the reaction with N,N-(4,4-diphenylmethane)bismaleimide(BMI).The structure,thermal property,and thermal reversibility of the resultant EP-DA are characterized by FT-IR,DSC,and gel-sol method.Results show that EP-DA gets the excellent reprocess ability and self-healing performance.(2)Repair behavior and mechanism of self-healing epoxy resin: The self-healing behavior of EP-DA is investigated by observing the change of cracks in EP-DA.Results reveal that the area of impacted cracks shrink gradually as the heat treatment time extending.Meanwhile,the healing rate of cracks becomes faster with the increase of heat treatment temperature.The self-healing performance and repeated self-healing efficiency are characterized by measuring the restoring quantity of flexural load.It proves that the healing efficiency for once impacted and healed sample is as much as 70% while the healing efficiency can still reach 50% when the self-healing epoxy resins are impacted and healed by the same way for three times.The self-healing mechanism of self-healing epoxy resins is explored through the measurement of self-healing behavior and self-healing effect after comprehensive analysis.(3)Preparation and properties of NBR toughened self-healing epoxy resin: To produce nitrile rubber(NBR)toughened self-healing epoxy resin(EP-DA-NBR),NBR is added during the preparation of epoxy resin.The structure of the resultant EP-DA-NBR is characterized by FT-IR.Results show that the thermally reversible DA bonds are existed in EP-DA-NBR.The mechanical properties of EP-DA-NBR with different amount of NBR are characterized by three-point bending test.Results reveal that with the increase of NBR additions,the flexural displacement of EP-DA-NBR increases gradually while the flexural load and strength decrease gradually.However,the flexural displacement of sample begins to reduce when the content of incorporated NBR is more than 10 phr.Therefore,it can be concluded that the optimal addition of NBR in EP-DA-NBR is 10 phr.(4)Repair behavior and mechanism of NBR toughened self-healing epoxy resin: The self-healing behavior of EP-DA-NBR is investigated by observing the change of cracks in sample.Results reveal that NBR can improve the healing effect of self-healing epoxy and with the increase of NBR additions;the self-healing effect of EP-DA-NBR improves gradually.The self-healing performance and repeated self-healing efficiency of EP-DA-NBR with different amount of NBR are characterized by measuring the restoring quantity of flexural load and flexural strength.It proves that the healing efficiency for once impacted and healed sample is as much as 80% while the healing efficiency can still reach 55% when the self-healing epoxy resins are impacted and healed by the same way for three times.The self-healing mechanism of self-healing epoxy resin and the effect of NBR on the healing efficiency of EP-DA-NBR are explored through the measurement of self-healing behavior and self-healing effect after comprehensive analysis.Results indicate that the self-healing property of EP-DA-NBR results from both thermal reversible DA reaction and thermal movement of molecular chains. |
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