Effects of Hydroxyethyl Cellulose Protection on Sizes and Thermal Conduction Behaviors of Boron Nitride Nanosheets Exfoliated from Ball-Milling and Homogenization

The sizes, shapes, and combination configurations of thermally conductive fillers critically influence the heat dissipation performance of their polymer composites. Herein, we combined ball-milling and homogenizing together to exfoliate hexagonal boron nitride (h-BN) by using hydroxyethyl cellulose (HEC) aqueous solution as medium, and then assembled the exfoliated boron nitride nanosheets (BNNSs) with aramid nanofibers (ANFs) to construct composite films, of which the mechanical properties and thermal conductivities were thoroughly investigated. The HEC solution with suitable viscosity could produce large size BNNSs due to the strong resistance to impacting forces during ball-milling, but overhigh viscosity would lower the lateral sizes and generate some nanoparticles (NPs) due to the poor dispersity of h-BN that may lead to direct contact between h-BN and milling balls. Homogenization further reduced the lateral sizes of BNNSs and produced abundant NPs; HEC protection could inhibit this size reducing trend but result in the in-homogeneous distribution of BNNSs and the formation of more NPs. Compared with the BNNSs alone, the hybrid of BNNSs and NPs yielded higher mechanical strength and thermal conductivity for the composites, possibly because the NPs could reinforce and bridge the BNNSs to form compact microstructure and highway for thermal conduction. Ultimately, we obtained the highest thermal conductivity of 39.25 W·m–1·K–1 for the ANF/BNNS composite films, which have the potential to be used as heat sink materials for the thermal management of electronic devices and batteries.