Pre-Envelope-Coating Strategy for Preparing the Boron Nitride Aramid Nanofiber Thermal-Insulating Composite Paper

To address the challenge that low thermal conductivity and weak interface bonding strength severely limit the improvement of thermal management efficiency, a synergistic "pre-envelope-coating" strategy is proposed through cross-scale structural design, which breaks through the limitations of the traditional trade-off between thermal conductivity and mechanical properties of materials. Hexagonal boron nitride (BN) was combined with aramid nanofibers (ANFs) via in situ polymerization to form a nano BN@ANFs pre-envelope structure. This structure was introduced into an aramid base paper through filling, significantly enhancing its mechanical strength and establishing an out-of-plane heat conduction path. Simultaneously, the paper surface was coated with a BNNS aramid resin solution, and an in-plane thermal conduction path was constructed by using water-assisted self-assembly. The BNNS/BN@ANFs aramid paper with a dual thermal network structure was successfully prepared by combining the above two methods. The composite paper exhibits outstanding performance, achieving an in-plane thermal conductivity of 2.77 W/mK and an out-of-plane thermal conductivity of 0.24 W/mK, representing increases of 265 and 500%, respectively, compared to the aramid base paper. Additionally, the composite paper also possesses a relatively high strength (16.88 MPa), which is 432% higher than that of the aramid-based paper, and it also has an excellent breakdown strength (36.72 kV/mm). Moreover, this composite paper also exhibits outstanding thermal stability, flame retardancy, and insulation properties, highlighting its potential applications in the fields of heat conduction and insulation.