Improvement of thermal conductivity of composite film composed of cellulose nanofiber and nanodiamond by optimizing process parameters

The in-plane thermal conductivity of cellulose nanofiber (CNF) composite film densely covered with nanodiamond (ND) particles has been improved by using the wet-rotating disc milling (WRDM) process and optimizing the compositional ratio of ND and CNF. The aspect ratio of CNF fibrils was increased by 42% using the WRDM. Furthermore, the in-plane thermal conductivities of CNF and ND/CNF films composed of WRDM-assisted CNF fibrils were improved with the increase of the aspect ratio of CNF fibrils. In addition, the mass ratio of ND to CNF and the in-plane thermal conductivity of the ND/CNF composite film were enhanced by using the WRDM-assisted ND suspensions owing to the improvement of dispersibility of ND particles. Consequently, the in-plane thermal conductivity of the ND/CNF film increased by 82% from 2.67 to 4.85 W/m K with the increase of the aspect ratio of CNF fibrils, thus improving the dispersibility of ND particles and optimizing the compositional ratio of ND and CNF. The dense adsorption of ND particles on the surface of CNF fibrils with high aspect ratio led to the improvement of the in-plane thermal conductivity of the composite film.