The Behavior Of Carbon Fiber Surface Oxidation And Its Effect On The Properties Of Carbon Fiber Reinforced Resin Matrix Composites

ABSTRACT:As the untreated carbon fiber surface is inert, it is difficult to form a strong interface bonding with the resin. So much attention has been paid to the surface modification. The oxidation mechanisms of carbon fiber in air and in the mixture acid of HNO3/H2SO4are studied systematically by using SEM, AFM, XPS, RAM, rotary rheometer and other techniques. Carbon fiber reinforced epoxy matrix composites and carbon fiber reinforced polyimide composites are made as well.The effect of above two methods of carbon fiber surface oxidation on the mechanical properties of carbon fiber reinforced resin composites is discussed widely. Main conclusions are as follows:(1) During the process of air oxidation, it is favorable to transform and-COOH with the increasing of temperature, but it has little effect on the content of-CO32-.(2)During the process of HNO3/H2SO4oxidation, the degree of etching of carbon fiber surface is strengthened within the oxidation time from1min to30min. The surface roughness of carbon fiber increases from9.5nm to25.4nm after an oxidation treatment of30min. The carbon fiber surface free energy increases with the extension of oxidation time at first,while the treatment over15min results in little increase.(3)During the process of HNO3/H2SO4oxidation,the S-, N-which are in the carbon fiber suface are transition groups and will be transformed into-COOH eventually. After a treatment of15min,the concentration of-COOH reaches its maximum.(4) During the process of air oxidation,the interface shear strength (IFSS)of carbon fiber reinforced epoxy resin matrix composites increases with the rising of air oxidation temperature firstly and then decreases.After an oxidation treatment of500℃,IFSS reaches a maximum.Compared with the untreated composites, IFSS increases from20.3MPa to36.9MPa.(5) Based on the polyimide DSC curve at different heating rates,this paper works out that the average reaction activation energy E is118.188KJ/mol, and the average reaction series n is0.923by Kissinger method and Ozawa method.What’s more, the cure kinetic equations of polyimide is obtained. Thus the suitable cure temperature is340℃. The polyimide curing shift TTT figure (time-temperature-transformation) is plotted.(6) During the process of HNO3/H2SO4oxidation,the IFSS of carbon fiber reinforced epoxy resin matrix composites increases with the rising of oxidation treatment time firstly and then decreases. Compared with the untreated composites, IFSS of CF/ER increases from20.3MPa to38.8MPa, and IFSS of CF/PI increases from67.5MPa to87.8MPa.