Enhanced Energy Absorption in 3D-Printed TPU Composites via Polydopamine-Modified Short Carbon Fibers

3D printing technology represents a pivotal methodology for the fabrication of carbon fiber composites characterized by intricate structural configurations. In pursuit of developing high-strength carbon fiber energy-absorbing structures (EAS), a strategy of blending thermoplastic polyurethane (TPU) with short carbon fiber (SCF) to combine both good flexibility and processability for the consequential fused deposition modeling (FDM) process is proposed. The interfacial adhesion between carbon fibers and TPU is considered with surface modification of carbon fibers with polydopamine coating, which is mainly based on the mechanisms of chemical bonding and physical interlocking, thereby enhancing the mechanical properties of the composites. More interestingly, the short carbon fibers exhibit alignment along the printing direction during the 3D printing process, which further enhances the mechanical strength of the composite material in that orientation. Furthermore, both the polydopamine coating and the orientation of carbon fibers were found to exert significant influences on the energy absorption properties of 3D-printed composites. When the carbon fiber content is 20%, the specific energy absorption (SEA) of TPU/SCF@PDA composites in the axial and transverse directions is increased by 114.3% and 193.6%, respectively, compared with that of pure TPU. Consequently, the strategic optimization of the polydopamine surface coating and the extrusion-induced alignment of carbon fibers present an efficacious approach for the fabrication of carbon fiber composites with superior strength and energy absorption capabilities.