Surface Modification Of Carbon Fiber And Analysis Of Mechanical Properties Of Its Composites

Carbon fiber reinforced resin matrix composites are receiving more and more attention in aerospace,medical,automotive,and energy fields due to many advantages such as high strength,light weight,and corrosion resistance.However,the smooth surface and chemical inertness of carbon fibers lead to poor interfacial adhesion between the carbon fiber surface and the resin matrix,which reduces the interfacial bond strength of the composites and limits their applications in some fields.Therefore,surface modification of carbon fibers is a hot issue that has been continuously explored by researchers,while the problems of polluted environment and harsh conditions in the modification process have been present.In this thesis,the surface of commercial carbon fibers was firstly de-sized by ultrasonic treatment.Then an experimental scheme was designed based on the mussel-inspired principle for surface modification of the pretreated carbon fibers.This method is simple to operate,has mild experimental conditions,and can effectively improve the mechanical properties of the composites.The main research contents of this thesis are as follows:Firstly,the surface of commercial carbon fiber is de-sized by acetone ultrasonic treatment.By changing the treatment time,the surface de-sizing of carbon fiber under different treatment time was investigated.The carbon fibers before and after de-sizing were characterized by scanning electron microscopy,infrared spectroscopy,Raman spectroscopy,X-ray photoelectron spectroscopy and X-ray diffraction.The experimental results show that the de-sizing treatment is the best when the treatment time is 6h.Secondly,based on the mussel inspired principle,polyethylene imine and gallic acid were used as raw materials to modify the surface of carbon fiber through Schiff base reaction or Michael addition reaction to produce polymer coating.The carbon fibers have been characterized before and after treatment by scanning electron microscopy,infrared spectroscopy,Raman spectroscopy,X-ray photoelectron spectroscopy,and X-ray diffractometer.The interlaminar shear and the bending properties of the composites were tested,and the influence of trimmed carbon fibers on the mechanical properties of the composites was evaluated.The experimental results show that the polymer coating is able to uniformly coat the carbon fiber surface when the mass ratio of polyethyleneimine and gallic acid is 1:1.This approach is able to enhance the interfacial bond between carbon fiber and matrix by introducing active functional groups on the carbon fiber surface.Compared with the untreated carbon fibers,the treated carbon fiber composites showed an increase in interlaminar shear strength,flexural modulus,and flexural strength by 26.99%,37.52%,and 26.63%,respectively.Finally,according to the mussel inspired principle,the surface of carbon fibers was modified by co deposition of gallic acid and aminopropyl terminated polydimethylsiloxane.It was characterized by scanning electron microscopy,infrared spectroscopy,Raman spectroscopy,X-ray photoelectron spectroscopy,and X-ray diffraction.The results show that gallic acid and aminopropyl terminated polydimethylsiloxane can undergo a Schiff base reaction or Michael addition reaction to form a polymer,which is deposited on the surface of carbon fibers,improving surface activity.By analyzing the interlaminar shear strength and bending properties of the composites,when the mass ratio of gallic acid and aminopropyl capped polydimethylsiloxane was 1:0.25,the interlaminar shear strength and bending modulus of the composites were the largest,and the interlaminar shear strength increased by 14.09% and the bending modulus increased by 26.83% compared with that of the untreated carbon fibers.The bending strength was highest when the mass ratio was 1:0.1,with an increase of 12.73%compared to the untreated carbon fibers.