| Carbon fiber has higher service temperature,high strength and stiffness,and lighter weight.It is widely used as the reinforcement of advanced polymer composites.However,due to the carbonization or graphitization of carbon fiber in the manufacturing process,the surface of carbon fiber is chemically inert,so it is difficult to form effective physical and chemical interaction with resin.However,the mechanical properties of carbon fiber reinforced polymer composites mainly depend on the interfacial bonding quality between carbon fiber and polymer matrix.Poor interfacial bonding will greatly limit the application of composites in high performance fields.It is necessary to improve the interfacial properties of composites by carbon fiber surface treatment.The surface treatment of carbon fiber is usually through the introduction of chemical functional groups or nanoparticles to the fiber surface to achieve the activation of the inert carbon fiber surface.At present,the research on the surface treatment of carbon fiber has been very diverse,but most of the methods have various shortcomings,such as environmental pollution,high cost,complex process,damage to the fiber itself and so on.In order to comply with the current concept of environmental protection and sustainable development,carbon fiber surface treatment should be studied in a low-cost,sustainable and environment-friendly direction.In this paper,based on the central idea of improving the interfacial bonding between carbon fiber and resin matrix,inspired by mussel adhesion protein,a low-cost,environmentally friendly and mild method was adopted to deal with carbon fiber without damaging the strength of the fiber itself.The main contents of this paper are as follows:(1)Inspired by mussel adhesion protein,according to the reaction mechanism of dopamine self-polymerization,a modified coating with good adhesion ability was formed on the surface of carbon fiber by Michael addition or Schiff base reaction using catechol and polyethyleneimine as raw materials.The modified carbon fiber was characterized by TGA,FTIR,Raman spectrum,XPS and dynamic contact angle.It was proved that the catechol-polyethyleneimine coating was successfully coated on the fiber surface.The best modification effect was obtained by controlling the ratio of catechol to polyethyleneimine.UV-vis spectra and SEM showed that the coating on the fiber surface was the most uniform when the ratio of catechol to polyethyleneimine was 1: 0.5.The test results of interfacial and mechanical properties show that the interfacial properties of carbon fiber / epoxy resin composites treated with catechol / polyethyleneimine are the best when the mass ratio of catechol to polyethyleneimine is 1: 0.5,the interfacial shear strength is 75.2 MPa,the interlaminar shear strength is 80.1 MPa,the transverse tensile strength is 32.1 MPa,and the bending strength is 976.4 MPa.Compared with untreated carbon fiber composites,it increased by 73.7%,51.7%,86.6%,51.9% respectively.The fracture surface of the composite was analyzed by SEM.The interface between carbon fiber and epoxy resin treated with catechol-polyethyleneimine was close,and the failure mode of the composite changed from interfacial failure to cohesion failure.(2)Inspired by the autopolymerization of dopamine,a modified coating with good adhesion ability was formed on the surface of carbon fiber by Michael addition or Schiff base reaction copolymerization using low-cost bio-based raw materials tannic acid and aminopropyl triethoxysilane as raw materials.The effect of copolymerization of tannic acid and aminopropyltriethoxysilane on the interfacial properties of carbon fiber composites was studied.The modified carbon fibers were characterized by SEM,TGA,FTIR,Raman spectroscopy,XPS and dynamic contact angle.It was proved that tannic acid-aminopropyltriethoxysilane was successfully modified on the surface of carbon fibers.The test results of interfacial and mechanical properties show that the interfacial properties of carbon fiber / epoxy resin composites treated by tannic acid-aminopropyltriethoxysilane co-deposition are obviously improved,and the interfacial shear strength is 73.5 MPa,interlaminar shear strength is 80.2 MPa,transverse tensile strength is 27.9 MPa,bending strength is 1028.1 MPa.Compared with untreated carbon fiber composites,it increased by71.3%,59.9%,58.5% and 33.2%,respectively.The fracture surface of the composite was analyzed by SEM.The interfacial bonding between carbon fiber and epoxy resin treated with tannic acid-aminopropyltriethoxysilane became better,and the failure mode of the composite changed from interfacial failure to cohesion failure.(3)inspired by the polymerization and adhesion of polydopamine,according to the Michael addition or Schiff base reaction of o-phenol hydroxyl group and amino group in dopamine during self-polymerization,Gallic acid with low cost biological group was selected as the raw material of o-phenol and gelatin was used as the raw material of amino group to react under conditions similar to the self-polymerization of dopamine.a copolymer with strong adhesion ability was formed on the surface of carbon fiber.In order to improve the surface activity of carbon fiber,increase the infiltration between carbon fiber and resin,and enhance the interaction between fiber and resin,so as to improve the interfacial properties of the composites.The modified carbon fibers were characterized by SEM,TGA,FTIR,Raman spectroscopy,XPS and dynamic contact angle.It was proved that Gallic acid-gelatin copolymer was modified on the surface of carbon fibers.The interfacial properties of carbon fiber epoxy resin composites treated by Gallic acid-gelatin co-deposition were significantly improved,the interfacial shear strength was 85.6 MPa,the interlaminar shear strength was 82.6 MPa,the bending strength was 1223.7 MPa;,compared with the untreated carbon fiber composites,the interfacial shear strength increased by 78.7%,56.4%,57.4%,respectively.After Gallic acid-gelatin treatment,the interfacial bonding between carbon fiber and epoxy resin is obviously improved,there is no gap between resin and fiber,and the failure mode of the composite changes from interfacial failure to cohesion failure. |
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