High thermally conductive, flexible and tough cellulose nanopaper functionalised with multiscale hexagonal boron nitride

Sustainable, flexible, tough, and thermally conductive substrates are critically required for next-generation green electronics. While cellulose nanopaper has emerged as a promising platform due to its high mechanical strength, it still exhibits limited elongation and thermal conductivity. Herein, multiscale hexagonal boron nitride (h-BN) was incorporated into a cellulose nanofiber (CNF) matrix to achieve a balanced combination of mechanical and thermal properties. Based on experimental results and Representative Volume Element (RVE) simulations, nanoscale h-BN enhances strength and flexibility by alleviating stress concentrations within the CNF matrix, whereas microscale h-BN forms continuous thermal conduction pathways to enable efficient heat transport. Compared with pristine CNF, the CNF/multiscale h-BN nanopaper exhibits a 52% increase in tensile strength, a 49% reduction in flexural stress, an 87% decrease in minimum bending radius, and a 100% enhancement in thermal conductivity. Moreover, the CNF/multiscale h-BN nanopaper exhibits mechanical strength and flexibility comparable to PI and PET, while achieving thermal conductivity approximately 10 times higher than that of PET and 5 times higher than that of PI. Electrical printing and heat dissipation demonstrations further validate its applicability as a sustainable substrate for next-generation flexible electronics.