Effects of carbon nanotube-polydopamine hybridization on the mechanical properties of short carbon fiber/polyetherimide composites

Recently, it is shown that hybrid sizing agents of nanomaterials and polymers are more effective than their single components in enhancing the mechanical properties of fiber reinforced polymer composites. However, the effects of the hybrid sizing agents are scarcely examined from both experimental and theoretical aspects. In this study, short carbon fiber (SCF) surfaces were modified by applying the hybrid sizing agents of polydopamine (PDA) and carbon nanotubes (CNTs). Then the polyetherimide (PEI) composites reinforced with modified SCFs were manufactured by extrusion compounding and injection molding techniques. A single fiber fragmentation test was experimentally carried out and the results were numerically analyzed to elucidate the effects of CNT-PDA sizing layer on the interfacial properties. The effects of hybrid sizing agent on the mechanical behaviors of PEI composites were investigated from both experiment work and theoretical predictions. The PEI composites with PDA-CNT treated SCFs exhibit the improved tensile strength at 25 °C and −60 °C due to the enhanced interfacial properties between SCFs and PEI after PDA-CNT treatment. The Fu-Lauke model predictions were conducted to interpret the reinforcing mechanisms of coated SCFs by hybrid sizing agent. Moreover, the temperature-dependent tensile behaviors of the composites were studied to examine the suitability of hybrid PDA-CNT sizing in modifying SCFs at various temperatures. Finally, the short term creep behavior of PEI composites was investigated by using Burger's model and the results indicate that the creep resistance of the PEI composites was obviously enhanced by the CNT-PDA sizing treatment at 25 °C.