Sustainable Overprinting of Recycled Carbon Fiber Reinforced Thermoplastic Composites With a Stabilized Surface Treatment Through In Situ Bonding

ABSTRACT This study presents a sustainable 3D overprinting approach for recycling of discontinuous carbon fibers from both thermoset and thermoplastic composites, incorporating a stable fiber surface treatment with polydopamine/silica nanoparticles (PDA/NPs). First, the thermal stability of this surface treatment for filaments during the recycling process was evaluated. Two representative types of polyphenylene sulphide (PPS) composites reinforced with treated carbon fiber, which are made with reclaimed carbon fibers from thermoset composites and reshaped carbon fibers from thermoplastic composites, were 3D printed and found to achieve improved mechanical strength by 26% and 22%, respectively. Results showed that reshaped rCF/PPS filaments exhibited the highest flexural strength at 253 MPa, which was subsequently selected for overprinting onto continuous carbon fiber reinforced polyamide 6 (CF/PA6) substrates via an in situ bonding technique. Laminates bonded with custom‐designed gradient rCF/PPS grids demonstrated a 37% increase in load‐bearing capacity, outperforming those strengthened with uniform rCF/PPS grids or even continuous carbon fiber/PPS (CF/PPS) grids. A custom five‐axis printer was further employed to deposit fibers along complex displacement paths on curved surfaces, highlighting the adaptability of this approach for nonplanar, intricate geometries.