Highly water-dispersed composite of cellulose nanofibers and boron nitride nanosheets

In this work, a composite of cellulose nanofibers (CNFs) and boron nitride nanosheets (BNNSs) with high dispersity in water is prepared via the combination of ball-milling and high-pressure homogenization, which is then transformed into paper-like film by vacuum assisted filtering and drying. The obtained CNF/BNNS dispersions can stably exist over 30 days without the observation of sediments. CNFs as a medium of ball-milling can protect the exfoliated BNNSs from being reaggregation and severely destroyed in violent collisions, and the BNNSs and CNFs can promote their exfoliation with each other. The hydrophilicity and electrostatic repulsion of CNFs, as well as the strong interfacial interactions and stereo-hindrance effects between one-dimensional (1D) CNFs and two-dimensional (2D) BNNSs are the reasons for the high dispersity of the composite in water, which in turn results in the favorable mechanical properties of the formed films. Although the introduction of BNNSs lowers the stress, strain, and toughness of the neat CNF films, but increases their modulus due to the stiffness of BNNSs. However, the thermal conductivities of the homogenized samples are inferior to the unhomogenized ones, as the decreased lateral sizes and excellent dispersibility of BNNSs are unfavorable to the formation of connective path of thermal conduction.