Influence Of Atmospheric Plasma Treatment On The Surface Properties Of Domestic PAN-Based Carbon Fibers

In the experiment the polyimide (PI) matrix with excellent thermal resistance comes into being with 4,4'-ODA and ODPA as the monomer and DMAc as the solvent. By bedding a PAN-based carbon fiber into PI, single fiber polyimide composites are made. In accordance to selection of random numbers, PAN-based carbon fibers are picked up for samples, then He/02 atmospheric pressure plasma is applied to modify PAN-based carbon fiber surface for Os,4s,8s and 16s,32s respectively. The Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Dynamic Contact Analysis System (DCAA) can help tell changes of carbon fiber surface topography, surface chemical composition of carbon fibers and fiber wettability respectively. In the meantime, the surface energy analyzed by DCAA tests increases, reaching the maximum when the plasma condition is set at 32s.Results show that He/02 atmospheric pressure plasma can introduce a large number of oxygen containing functional groups onto the fiber surface, which may increase the polarity of fiber surface; In addition, it has the etching effect on the surface. With plasma-treated time on the rise, surface morphology changed significantly. When the treatment time comes to 32s, the surface groove slightly deepens.Theory of Weibull helps analyze and evaluate data drawn from the fiber tensile strength test with the interfacial bonding strength the carbon fiber and polyimide matrix evaluated by the interfacial shear strength (IFSS). It is found the smaller the gauge length, the larger the tensile strength, with the lower data variance. What's more, plasma treatment makes no difference to the fibers. The carbon fiber tensile strength and variance of data are almost independent of the plasma treatment. When the tensile gauge lengths amounts to 5mm and 10mm, the tensile strength of carbon fiber increases slightly. With tensile gauge length of 10mm and the treatment time of 16s, the interfacial shear strength between fibers and polyimide matrix increases from 107.1Mpa to 147.9Mpa by 38.0%. With the treatment time of 16s, the interfacial shear strength between fibers and polyimide matrix increases only by 38.0%. The conclusion can be drawn that longer plasma treatment time will weaken the increasing trend of the interfacial bonding strength of the carbon fiber and polyimide matrix. Hence, it is needed to control the treatment time properly.The effects of plasma treatment on PAN-based carbon fiber surface and polyimide matrix interfacial properties are significant. Changes of interfacial shear strength (IFSS) are affected by many factors. The increasing polar groups after plasma treatment forms covalent bond and hydrogen bonding with the C=O and COOH groups in the chain of polyimide prepolymer, and in turn enhances the interfacial shear strength. The surface oxygen content of treated carbon fiber increases with the number of polar groups on the rise. At the same time surface energy and the wetting property after the plasma treatment are improved.