Objective This study aims to use carbonized hemp fibers to build a 3D thermal network, so as to solve problems like reduced strength, poor processability, and higher cost caused by high boron nitride (BN) filler content in epoxy composites, thereby enhancing the thermal conductivity of epoxy resin (EP).

Method Carbonized hemp fibers (C) were selected as the base framework material and combined with BN to create a synergistic composite framework with high thermal potential. EP was used as the matrix to fabricate the BN-C/EP composite with enhanced thermal conductivity. The formation mechanism and working principles of internal 3D thermal network were investigated by characterizing the microstructure, chemical composition, mechanical properties, thermal conductivity, and heat dissipation performance of the materials.

Result (1) In the BN-C/EP composite, carbonized hemp fibers interwove and synergized with modified BN, forming a rich 3D thermal conduction network. The thermal conductivity increased by 496% compared with EP, and the thermal conductivity per unit filler increased by 58.63%, effectively reducing the amount of filler needed and lowering costs. (2) In through-plane thermal conductivity tests, the thermal conductivity efficiency of BN-C/EP composites increased by 11.95% compared with EP. In in-plane heat dissipation tests, the heat dissipation efficiency increased by 23.33% compared with EP. These results indicated that the material had good potential for applications in through-plane thermal conductivity and in-plane heat dissipation (such as heat sinks). (3) The flexural strength of BN-C/EP composite increased to 68.7 MPa, an improvement of 2.08% over EP and 9.74% over BN/EP, meeting the requirements for use as a thermal interface material.

Conclusion This study used high-aspect-ratio carbonized hemp fibers to build a 3D thermal network in BN-C/EP composites, which improved thermal conductivity significantly. It reveals the key role of hemp fibers in forming the network. Their natural, eco-friendly, and low-cost nature offers new ideas for composite development. Future work can explore the synergy between natural fibers and fillers, optimize composite microstructures, and develop higher-performance, greener composites to meet the industrial demand for efficient thermal management.