Tough Photopolymerizable Resin Matrices for Additively Manufactured Continuous Carbon Fiber‐Reinforced Composites

ABSTRACT Additive manufacturing (AM) of composites is gaining popularity due to the ability to quickly 3D print tough and durable composite parts on demand. As carbon fiber (CF) is the most common reinforcement candidate for AM composite production parts, increasing the toughness and durability of 3D‐printed thermoset composites reinforced with continuous CF tow is of great importance. To this end, we adapted three tough low‐viscosity photocurable resin formulations consisting of a commercial urethane acrylate resin (a matrix system that bonds well with CF) and petrochemical ( N ‐vinylpyrrolidone, NVP) and bio‐derived (3,4‐dimethoxystyrene, VV) reactive diluents as matrices for AM of continuous CF composites in a custom 3D printing process. The resin formulations demonstrated high double bond conversion in the two‐step process consisting of photocuring and thermal postcuring. The mechanical properties of the AM composites showed distinction from the properties of urethane acrylate‐based composites reported in prior literature. In this study, these properties were compared as a function of reactive diluent in the formulations. The tensile properties of AM composites printed using the three resins were similar and fell within the expected range based on their fiber volume fraction. However, the flexural and fracture behavior of the resins was strongly dependent on the type of reactive diluent used. Aromatic VV increased flexural strength and modulus, whereas NVP, a cyclic lactam, resulted in enhanced ability of the composites to absorb and dissipate impact energy. Overall, the resins demonstrated their effectiveness as matrices in AM of continuous CF composites.