Characterization Of Surface Energy, Surface Roughness And Chemical Component Of Carbon Fibers

Carbon fiber and its composites have been widely used in aircraft, missiles, automobile parts and many other fields, because of its high strength, high modulus and excellent fatigue performance. Surface characteristics can influence the properties of carbon fibers and their composites. of In the work, the methods to measure surface energy, surface roughness and chemical component of carbon fiber stably were determined. The differences between surface properties of domestic carbon fiber and Japanese carbon fiber (T300) have been investigated. Then the relationship between the processing temperatures and surface properties of domestic and T300 carbon fibers were also studied.The methods of testing the surface characteristics were determined in the work. In the method to test the surface energy of carbon fiber, the surface tensionmeter was used. Effects of the specimen preparing method and testing parameters on results were systematically studied. Finally, the specimen preparing method was standardized and the testing parameters were determined. The roughness of carbon fiber was tested by atom force microscope (AFM). In the roughness method, the optimum scanning area was determined assisted with laser scanning confocal microscope. The chemical component of carbon fiber was tested by X-ray photoelectron spectroscopy (XPS). Through the study of tested repeatability and the trend of etching, the state of sample and instrument paramenters were determined.Based on the determined stable methods, a systematic analysis of surface energy, polar parts and dispersive parts, surface morphology, roughness and chemical component of domestic carbon fiber and T300 was studied. Different blocks of carbon fibers had different surface characteristics. For the blocks of carbon fiber with stable characteristics, the polar surface energy of domestic carbon fiber was lower than that of T300. It was not favorable for the well wettability between domestic carbon fiber and resin during preparing composite materials. It was found that there were a number of grooves which uniformly dispersed on their surface. The depth of grooves on the surface of domestic carbon fiber was smaller than that of T300. The results of roughness measured by AFM showed that the roughness of domestic carbon fiber and T300 belonged to one range. The chemical characteristic comparison of two kinds of fibers was investigated by XPS. The results showed that the element contents of domestic carbon fiber were C, Si, which were higher than C,Si of T300. O, N of domestic carbon fiber were lower than O, N of T300. In order to investigate differences in the bodies of them, surface etching has been done. It was found that O, Si element contents of domestic carbon fiber were higher than O, Si of T300 and the other element contents were lower. Contents of functional groups were calculated by fitting C1s spectra. The results showed that there were three kinds of function groups (-C-C-, -C-O-, -O-C=O)on the surface of carbon fiber. The -C-C- content of domestic carbon fiber was higher than that of T300 and the -O-C=O content was lower.The changes of surface characteristics of carbon fiber treated in manufacturing process of composites were determined. Carbon fibers were treated with programmed controlled temperature experiment which was aimed to simulate actual process of manufacturing composite materials. Taking manufacturing process of CF/BMI composite for example, three temperature stages were chosen, 150℃, 180℃, 200℃. The results showed that the surface energies of domestic carbon fiber and T300 treated at 150℃were highest. Combined with SEM and AFM images, it was found that the roughness of domestic carbon fiber went higher as the treating temperature rose. The roughness of T300 increased when the temperature was lower than 180℃and decreased when it was higher than 180℃. Element contents of the two types of carbon fibers changed after they were treated at different temperatures. Treated at 180℃, the C contents on the surface of both domestic carbon fiber and T300 were lowest, but the O contents were highest.Change of mechanical properties of carbon fiber with manufacturing process of composites was studied. The relationship between filament tensile strength and treating temperatures was investigated by filament strength test and Weibull distribution models. The results showed that tensile strength of domestic carbon fiber was influenced more obviously than that of T300.