Investigation of Surface Treatment of Carbon Fiber by Dynamic Method in the Polyurethane Composites

Polyacrylonitrile (PAN)-based carbon fibers were chemically modified with a different ratio of Sulfuric acid (SA) to Nitric acid (NA), then reinforced Polyurethane (PU) composites in the presence of carbon fibers were prepared. The structural and surface characteristics of the modified carbon fibers were investigated by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The FTIR results showed the presence of the carbonyl groups in a higher ratio of NA and the formation of carboxyl groups in a lower ratio of NA. The interaction between carbon fiber and PU matrix was studied by the dynamic mechanical thermal analysis (DMTA) method. The DMTA results showed with increasing carbon fiber/PU matrix interaction, the intensity of glass transition temperature decreased. Matching the DMTA results with the power-law model and Cole-Cole diagram showed that the process of carbon fiber modification can increase the amount of chain with a long relaxation time in the PU matrix.