Highly Exfoliated Boron Nitride Nanosheets via Carboxyl Nanocellulose for Thermally Conductive Nanocomposite Films

The continuous development of electronic devices toward high-power and integrated directions has led to an increasing demand for renewable polymer composite materials with high thermal conductivity and electrical insulation to solve the problem of overheating in electronic devices. Cellulose is inherently insulating, with insufficient thermal conductivity. Although boron nitride nanosheets (BNNSs) have excellent thermal conductivity, hexagonal boron nitride (h-BN) ligands in their raw state are prone to aggregation, which limits their performance. In this work, h-BN was first ball-milled and amino-modified, and then, carboxylated nanofibrillated cellulose (COOH-CNF) was used to disperse the BNNSs. With the help of amide bonding, the BNNSs were uniformly dispersed in the nanocellulose (CNF) matrix; this reduced the aggregation and the presence of voids between the BNNSs and promoted the construction of effective thermal channels. The resulting composite slurry was stably dispersed and could be filtered to form a film; the best overall performance was achieved for a BNNS loading of 30% with a thermal conductivity (TC) of 9.00 W·m–1·K–1 (pure CNF 1.88 W·m–1·K–1). In addition, the volume resistivity reached 9.38 × 1013 Ω·cm (pure CNF of 2.53 × 1013 Ω·cm) and the electrical strength reached 22.67 kV·mm (17.04 kV·mm for CNF). Our results showed that the BNNS-CNF composite film had high TC and excellent insulating properties; therefore, its application in the thermal management of electronic devices has broad application prospects.