A polyacrylonitrile-based carbon fiber modified with multi-walled carbon nanotubes (MWNTs) was prepared in this paper.Three chitosan derivatives

phthaloyl chitosan(PhthCS)

naphthoyl chitosan and carboxymethyl chitosan

were used for surface treatments of MWNTs in order to improve their dispersion and stability.Acidizing MWNTs and original MWNTs were also used for comparison with the MWNTs treated with chitosan derivatives.Results indicate that the dispersion and stability of PhthCS-MWNTs were improved significantly in those solvents possessed of polarity from 6 to 10. The effects of molecular weight and concentration of PhthCS on the dispersion stability of the MWNTs were evaluated.Results of transmission electron microscopy and element analysis of the MWNTs reveal that part of MWNTs surfaces are coated by a layer of PhthCS with the thickness of 5 ~ 10 nm

which changes the surface properties and dispersion stability of the MWNTs.A composite PhthCS-MWNTs/carbon fiber was fabricated through gel-spinning

preoxidation

low-temperature carbonization and high-temperature carbonization.SEM results exhibit that the PhthCS-MWNTs dispersed uniformly and oriented preferentially within the composite fibers

which led to improved mechanical properties of the composite carbon fiber.The tensile strength of the composite carbon fiber with 0.5% PhthCS-MWNTs is 19.8% higher than that of the carbon fiber without MWNTs.And the Youngs modulus of the composite carbon fiber containing 3% PhthCS-MWNTs is 13.86 GPa

which is 122% higher than that of the carbon fiber without MWNTs.However

the elongation at break of the composite carbon fiber changed scarcely by adding the PhthCS-MWNTs.