<scp>3D</scp> Printing of Continuous Carbon Fiber Reinforced Composites With Cyanate Ester Interpenetrating Polymer Networks for Enhanced Thermo‐Mechanical Properties

ABSTRACT The growing demand for lightweight, multifunctional materials has positioned additive manufacturing (AM) as a transformative approach for fabricating advanced composites. But the fabrication of via AM remains a challenge due to limited fiber alignment and compatibility in thermoset systems. This study demonstrates a novel method to manufacture high‐performance, multifunctional composites using Direct Ink Writing (DIW) with in situ impregnation of continuous carbon fiber (CCF) into cyanate ester and tris(2‐hydroxyethyl) isocyanurate triacrylate interpenetrating polymer network resins. This allows for continuous fiber deposition and UV–thermal curing during and after printing to solidify the polymer matrix, enabling strong fiber–matrix interfaces and structural integrity. The optimized formulation achieved rapid in situ curing, maintaining fiber placement during complex print paths. The resulting composites exhibited substantial improvements in mechanical, thermal, and electrical properties. Flexural strength and modulus increased by over 300% compared to the unreinforced polymer matrix, reaching 280.12 ± 25.19 MPa and 19.77 ± 0.96 GPa, respectively, at a fiber volume fraction of 11.9 vol% ± 0.3 vol%. The glass transition temperature improved 4.7% (up to 300°C), indicating superior thermal stability. Additionally, the longitudinal electrical conductivity reached 407.04 ± 88 S/m, more than 4 × 10 10 increase compared to unreinforced. Microscopic analysis revealed progressive failure mechanisms such as fiber bridging and pull‐out, contributing to enhanced damage tolerance. This work demonstrates a scalable route for integrating CCF with thermosetting matrices in a single‐step 3D printing process and highlights the potential of DIW‐based strategies for manufacturing structurally and functionally optimized composites for electronics and high‐temperature applications.