Preparation And Properties Research Of Imide Skeleton Hyperbranched Epoxy Resin/Carbon Fiber Composites

Carbon fiber reinforced polymer composites（CFRP）are widely used in aerospace and wind power fields because of their low density,corrosion resistance and excellent mechanical performance.Due to the smooth surface and chemical inertia of carbon fiber,it is difficult to form a strong interfacial interaction between carbon fiber and matrix resin and obtain high performance composites.As the most widely used matrix resin in CFRP,thermosetting epoxy resin can obtain excellent comprehensive performance of CFRP,but its irreversible three-dimensional cross-linking structure makes it difficult to degrade and recycle.In this paper,degradable imide skeleton hyperbranched epoxy resin was synthesized based on esterification reaction and thiol-ene click reaction.The surface chemical activity and roughness of carbon fiber were improved by thiol-ene click reaction.High performance degradable imide skeleton hyperbranched epoxy resin/carbon fiber composites were prepared,which could be degraded efficiently and recycled carbon fiber without lossless under acidic conditions.The specific research contents are as follows:（1）Synthesis and characterization of degradable imide skeleton hyperbranched epoxy resin.Firstly,hydroxyl-terminated hyperbranched polymers（DPI-n,n=6,12,24）with different molecular weights were synthesized by the reaction of 4-methylidene-bis（N-trimellidene）diphenylmethane（DTA）with tris（2-hydroxyethyl）isocyanurate（THEIC）.Thiol-terminated hyperbranched polymers（DSPI-n,n=6,12,24）were synthesized by the reaction of DPI-n with3-mercaptopropionic acid（MPA）.Finally,hyperbranched epoxy resins（DIHE-n,n=6,12,24）were synthesized by thiol-ene click reaction.The chemical structure and molecular weight of DTA,DPI-n,DSPI-n and DIHE-n were characterized by FT-IR,¹H NMR and GPC.（2）Surface modification of carbon fiber and preparation and performance of imide hyperbranched epoxy resin/carbon fiber composites.DSPI-n was grafted onto the surface of carbon fiber by thiol-ene click reaction to improve the surface roughness,wettability and performance of carbon fiber.The chemical structure and surface morphology of pristine carbon fiber（PCF）and treated carbon fiber（TCF）were analyzed systematically by FT-IR,Raman,SEM and TGA.The monofilament tensile strength and modulus of the TCF were5.20±0.61 GPa and 327.83±33.48 GPa,which increased by 59.51%and 25.46%,respectively.The effects of molecular weight of DSPI-n,irradiation time,-SH content,catalyst dosage,molecular weight and volume fraction of DIHE-n on the mechanical performance of imide skeleton hyperbranched epoxy resin/carbon fiber composites were discussed.The mechanical performance of the composites increased at first and then decreased with the increase of molecular weight of DSPI-n,irradiation time,-SH content,catalyst dosage,molecular weight and volume fraction of DIHE-n.Finally,the conditions of higher comprehensive performance were as follows:DIHE-12 was matrix resin,DSPI-12modified carbon fiber,irradiation time was 40 min,-SH content was 6 mmol/g CF,catalyst was 1 wt%and the volume fraction of DIHE-12 was 50%.The maximum tensile strength and flexural strength of the composites were 754.91±22.87 MPa and 211.30±6.59 MPa.The interlaminar shear strength（ILSS）and interfacial shear strength（IFSS）of DIHE-12/TCF were 31.48±2.56 MPa and 54.95±1.82 MPa,which increased by 49.34%and 67.89%compared with DIHE-12/PCF,respectively.The click reaction increased the surface roughness and chemical activity of carbon fiber,which made the bond between TCF and resin closer,which was beneficial to the formation of strong mechanical interlock and chemical binding between TCF and matrix resin at the interface.（3）Study on degradation behavior of DIHE-12/TCF.The factors affecting the degradation degree of composites（volume ratio of H₃PO₄ to H₂O₂,concentration of H₃PO₄,degradation temperature,mass ratio of DIHE-12/TCF to degradation solution and degradation time）were discussed systematically.The optimum conditions for complete degradation of DIHE-12/TCF were obtained as follows:the volume ratio of H₃PO₄ to H₂O₂ was 2:8,the concentration of H₃PO₄ was 1.5 mol/L,the degradation temperature was 90℃,the mass ratio of DIHE-12/TCF to degradation solution was 1:40,and the degradation time was 8 h.The degradation mechanism of DIHE-12/TCF was investigated by GC-MS.The analysis of monofilament tensile strength,surface morphology and chemical structure of recycled carbon fiber（RCF）shown that the surface morphology and chemical properties of RCF were not obviously damaged,indicating the non-destructive recovery of carbon fiber in the composites.