Amino Acid-Assisted Sand-Milling Exfoliation of Boron Nitride Nanosheets for High Thermally Conductive Thermoplastic Polyurethane Composites

Boron nitride nanosheets (BNNSs) show excellent thermal, electrical, optical, and mechanical properties. They are often used as fillers in polymers to prepare thermally conductive composites, which are used in the production of materials for thermal management, such as electronic packaging. Aside from the van der Waals force, there are some ionic bond forces between hexagonal boron nitride (h-BN) layers that result in high energy consumption and make BNNSs easily agglomerate. To overcome this issue, L-lysine (Lys) was first employed as a stripping assistant for preparing graft-functionalized BNNSs via mechanical sand-milling technology, and the obtained Lys@BNNSs can be added into thermoplastic polyurethane (TPU) by solution mixing and hot-pressing methods to prepare thermally conductive composites. This green and scalable method of amino acid-assisted sand-milling can not only exfoliate the bulk h-BN successfully into few-layer BNNSs but also graft Lys onto the surface or edges of BNNSs through Lewis acid-base interaction. Furthermore, benefiting from Lys's highly reactive groups and biocompatibility, the compatibility between functionalized BNNSs and the TPU matrix is significantly enhanced, and the thermal conductivity and mechanical properties of the composite are remarkably increased. When the load of Lys@BNNSs is 3 wt%, the thermal conductivity and tensile strength of the obtained composites are 90% and 16% higher than those of the pure TPU, respectively. With better thermal and mechanical properties, Lys@BNNS/TPU composites can be used as a kind of heat dissipation material and have potential applications in the field of thermal management materials.