Electrostatic self-assembly of ZIF-8 and boron nitride for high-performance polytetrafluoroethylene composites with superior thermal conductivity and tunable thermal expansion properties

The thermally conductive functional material ZIF-8/BN was co-loaded onto the fiber via electrostatic self-assembly. • The effects of stabilization heat treatment on the morphology and properties of the reinforcement were investigated. • The roles of uniform ZIF-8 and ZIF-8/BN nanoparticles loaded at the resin-reinforcement interface were analyzed. • Composites obtained solely via reinforcement functionalization showed excellent thermal expansion and thermal conductivity. Polytetrafluoroethylene (PTFE) is widely used in high-frequency substrate materials due to its favorable dielectric constant and excellent thermal stability. However, its high coefficient of thermal expansion (CTE) and low thermal conductivity cause some processing challenges. Herein, we report a modified reinforcement, designated ZIF-8/BN@GF (ZB@G), which was fabricated by electrostatically assembling thermally conductive BN (boron nitride) with the metal-organic framework (MOF), followed by in-situ growth onto glass fibers (GF) through an impregnation process. Thermal stabilization was found to markedly enhance the structural compactness and moisture resistance of the fibers during processing. The rough surface morphology of the MOF facilitates mechanical interlocking and resin infiltration into its porous structure, thereby strengthening the interfacial bonding between the reinforcement and the resin matrix and consequently improving the dimensional stability of the composites. Moreover, the uniform distribution of flat BN nanosheets along the fiber surface serves to regulate interfacial interactions, establish oriented thermal conduction pathways, and simultaneously tailor the thermal expansion behavior. As a result, the resulting PTFE composites exhibit a suitable in-plane CTE parallel to the reinforcement of 16.97 ppm/°C and a maximum thermal conductivity of 1.481 W·m −1 ·K −1 . In addition, they retain excellent dielectric properties, achieving a low dielectric constant of 2.39 and a low dielectric loss of 0.00145 at 10 GHz. This work demonstrates that a straightforward in-situ loading of nano-functional materials onto reinforcements can concurrently deliver substantial improvements in thermal conductivity and mechanical performance, providing a promising strategy for the selection of reinforcements in next-generation high-frequency substrate materials. Download: Download high-res image (155KB) Download: Download full-size image