B Fathi - Polymer Research Laboratory, Iran R &D Center for Chemical Industry, Karaj, Iran
M Esfandeh - Composites Department, Iran Polymer and Petrochemical Institute, Tehran, Iran
A Khalifeh Soltani - Composite Materials Research Center, Malek Ashtar University of Technology, Tehran, Iran
I Amiri Amraei - Composite Materials Research Center, Malek Ashtar University of Technology, Tehran, Iran

In fiber reinforced composites, the interface of fiber/matrix plays an important role in the mechanical performance of the composite. In this study, the surface modification of poly (acrylonitrile) based carbon fiber by various concentrations of sulfuric acid is investigated. To this end, Atomic Force Microscopy (AFM) was employed to capture the corresponding changes in the surface roughness of the carbon fiber and the results were compared with that of the untreated fibers. Moreover, using treated and untreated fibers, unsaturated polyester resin/carbon fiber unidirectional composite rods were prepared and their flexural properties were determined by three-point bending and dynamic mechanical thermal analysis. The results indicated that the carbon fiber surface roughness increases slightly over the whole investigated concentration range. Furthermore, composite rods that were made from treated fibers exhibited improved flexural properties. It is also found that treating the fiber decreases the magnitude of loss modulus. Besides, the flexural strength of composites made of the treated carbon fiber (by 10% wt of the sulfuric acid) increased by 20%. Since all other parameters were kept constant over the tests, the differences observed in the composite behavior can only be attributed to the interfacial phenomena.

Carbon fiber, Adhesion, Chemical treatment, unidirectional composites, DMTA