Improvement of mechanical and physical properties of carbon fiber-reinforced polyamide composites by applying different surface coatings for short carbon fiber

In this study, short carbon fiber (CF) surface was coated with jeffamine, isocyanate, and polyamide (PA). Surface-coated layers of CF samples were confirmed by infrared spectroscopy. Desized and coated CFs were incorporated to PA6 by melt-compounding method with a constant ratio of 20 wt%. Tensile testing, shore hardness, dynamic mechanical analysis (DMA), and melt flow rate (MFR) test of composites were performed. Adhesion of CF to the polymer matrix was investigated by scanning electron microscopy (SEM) of composites. Mechanical characterization of composites implied that tensile strength, tensile modulus, percent elongation, and shore hardness of unfilled PA were extended to higher values by the addition of surface-coated CFs. The highest improvement was observed for isocyanate-modified CF-loaded PA-based composites. According to DMA results, storage modulus and loss modulus of PA increased with the incorporation of sized CF into polymer matrix. CF containing composites showed higher glass transition temperature with respect to unfilled PA. Addition of CF caused no significant change for MFR of PA. Poor adhesion of desized CF and relatively strong adhesion of surface-coated CFs to PA matrix were confirmed by SEM analysis.