| Carbon fiber reinforced thermosetting polymer composites(CFRP)are widely used in aerospace,automotive,and wind turbine blade industries because of their high specific strength,excellent mechanical properties,and chemical resistance.However,the irreversible cross-linked structure of thermosetting polymer composites leads to the prepared composites difficult to degrade and recycle,and the amount of solid waste is also increasing sharply.At present,both physical and chemical recycling methods for composites cannot effectively recover thermosetting resin and carbon fiber at the same time.Based on the strong covalent bond and acid sensitivity of the hexahydro-s-triazine structure,to solve the recycling of thermosetting CFRP and improve the mechanical properties of the composites.A degradable hyperbranched epoxy resin(HT3)containing hexahydro-s-triazine structure was synthesized,and the thiol-ene click reaction was used to improve the wettability of the carbon fiber surface.At the same time,degradable hyperbranched epoxy resin/carbon fiber composites were prepared,and the closed-loop recycling of the epoxy resin/carbon fiber composites was realized by studying the degradation mechanism.The main research content is as follows:(1)Surface modification of carbon fiber.The surface modification of carbon fiber was carried out by using mercaptans with different functionalities through the thiol-ene click reaction to obtain functionalized carbon fiber(TCF).The carbon fiber structure was characterized by FT-IR and Raman.The properties of the initial carbon fiber(PCF)and TCF were characterized by automatic surface tensiometer,SEM,TGA,and universal material tester.The results show that the rolling angle of TCF(29.3°)is greater than the rolling angle of PCF(14.8°).The chemical activity of the carbon fiber surface was increased after modification,which proved that the sulfhydryl functionalized carbon fiber had good wettability between the carbon fiber and the resin.The strength of carbon fiber modified by BTMP-6 was the highest,reaching 3.95 GPa,while a decrease of the char yield variation rate of functionalized carbon fiber when the content of BTMP-6 was reduced.(2)Performance of degradable hyperbranched epoxy/carbon fiber composites.The degradable hyperbranched epoxy resin/carbon fiber composites(HT3/TCF)were prepared from the degradable hyperbranched epoxy resin(HT3)and TCF.The influence of the amount of HT3 and different matrix resins on the properties of HT3/TCF composites was studied.As the amount of HT3 increase,the mechanical properties of the composites increased first and then decreased.When the HT3 content is 55 wt%,the mechanical properties of the composites reached the maximum value.Compared with 35 wt%of HT3 content,the tensile strength,tensile modulus,flexural strength,and flexural modulus of 35 wt%carbon fiber composites increased by 38.14%,63.23%,24.05%,and 88.01%,respectively.Compared with the traditional diglycidyl ether of bisphenol-A(DGEBA)/PCF composites,the strength and modulus of the new HT3/TCF composites were significantly improved,and its tensile strength,flexural strength,tensile modulus,and flexural modulus were increased by 58.16%,146.71%,42.30%,and 164.98%,respectively.Compared with the original HT3/PCF composites,the interfacial shear strength(IFSS)and interlaminar shear strength(ILSS)of the modified HT3/TCF composites increased by 80.14%and 170.25%,respectively.Analyzed the carbon fiber composites interface reinforcement mechanism by SEM.The service life of HT3/TCF composites was studied by acid resistance and sea water resistance experiments.(3)Recycling of degradable hyperbranched epoxy resin/carbon fiber composites.First,the composites were degraded by a mixed solution of HCOOH and THF to realize the recycling of the resin.The structure of the degradation product of the HT3/TCF composites was characterized by using FT-IR,1H NMR,and GPC,and the degradation mechanism of HT3/TCF composites was studied by GC-MS.The cured composites are controllably depolymerized into monomers and oligomers with high recyclability,which can be utilized to prepared HT3 and the precursor of crosslinked HT3.Secondly,the H3PO4/THF solution degradation composites were used to realize the recycling of carbon fiber cloth.The regenerated carbon fiber was characterized by SEM and Raman spectroscopy,and the mechanical properties of a single carbon fiber were studied.The monofilament of the regenerated carbon fiber still retains the strength of the original fiber,which proved the non-destructive recovery of the carbon fiber.100%of the carbon fibers are recovered and reused to fabricate new composites without deterioration of performance.The results provide a method for designing high-performance composites and a new pathway for highly efficient closed-loop recycling. |
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