Continuous carbon fiber Additive Preforming and its application for the fabrication of epoxy composites

This study presents Additive Preforming, a novel technique for manufacturing continuous fiber-reinforced polymer composites. The new technique consists of 3D printing continuous fiber filaments coated with a suitable thermoplastic for the fabrication of continuous fiber preforms. These preforms can eventually be used to produce thermoset composite parts. The manufacturing technology used here to produce epoxy-carbon composites involved coating a continuous carbon fiber roving with a thermoplastic polymer (binder) to produce a 3D-printable filament. This filament was then 3D-printed to create a preform, and the final composite was obtained by impregnating the preform with the epoxy matrix. To optimize the final properties of the epoxy-carbon composite, a screening protocol for potential thermoplastic binders was developed and implemented. This protocol aimed to identify the most compatible/miscible binders for the epoxy resin. The evaluation was conducted using Hansen's solubility parameters, interfacial tension determinations, and optical microscopy observations. The results identified polycarbonate (PC) and phenoxy resin (PH) as the most suitable candidates. The mechanical properties of the composites were strongly influenced by the binder used, and the best properties (elastic modulus of 32 GPa and flexural strength of 609 MPa) were achieved when PH was used. The carbon fiber content of the composites was also optimized by comparing the mechanical properties of the composites obtained with 12 and 24 k carbon fibers. The resulting epoxy composites – made of phenoxy-coated continuous carbon fibers and containing approximately 40 wt% of carbon fibers – featured an elasticity modulus of 62 GPa and flexural strength of 852 MPa. Highlights: Additive Preforming is proposed for manufacturing CFPCs. Continuous carbon fiber is coated and 3D-printed prior to impregnation in epoxy. The established screening protocol ranks binders based on their compatibility. PH was identified as the optimum binder and was validated by mechanical tests. The optimization of the fiber content led to superior mechanical properties.