Enhancing the through-plane thermal conductivity of a cellulose nanofiber film via boron nitride surface functionalization and cellulose chemical crosslinking

In this study, a hybrid filler comprising cellulose nanofiber (CNF) and boron nitride (BN) (CNF-BN) was fabricated through the ball milling exfoliation method by introducing oxalic acid to provide hydroxyl groups, leading to better compatibility between CNF and BN via hydrogen bonding. After functionalization and CNF grafting, the filler was dispersed sufficiently into the CNF matrix with tetraethyl orthosilicate for chemical crosslinking. The c-CNF-BN/CNF film was then fabricated by vacuum infiltration. The voids and defects of the film surface decreased due to the tangled cellulose nanofiber with the help of a crosslinking agent, facilitating the construction of an efficient heat pathway. As a result, the through-plane thermal conductivity increased from 0.5 W m(-1) K-1 to 1.69W m(-1) K-1 with 37.5 vol% BN loading, showing a thermal conductivity enhancement of 238% compared to the raw CNF film. Additionally, the mechanical property was also enhanced. The tensile stress was 42.2 MPa and elongation at break was 36.8%. Thus, the c-CNF-BN/CNF film can be used as a composite for efficient thermal management in electronic devices.