Few-Layered Boron Nitride Nanosheets for Strengthening Polyurethane Hydrogels

Two-dimensional hexagonal boron nitride nanosheets (BNNS) are an outstanding filler and additive, since they are transparent, thermally stable, and chemically inert. However, it is difficult to obtain few-layered BNNS with large lateral sizes in an efficient way due to the strong interlayer interactions in h-BN. Herein, a facile and efficient molten salt-assisted synthesis has been developed to prepare few-layered BNNS with a few microns in lateral size. Ammonia borane was mixed with KCl and NaCl and then heated to 1000 °C and held for 2 min, and the resultant powders were sonicated in water to produce hydroxylated BNNS. Used as an additive with 0.066 wt % loading, the functionalized BNNS can effectively improve the mechanical modulus of polyurethane (PU) hydrogels from 1635 to 2776 kPa, and the optical property of the hydrogel is not compromised. The BNNS-reinforced PU hydrogel with significantly improved mechanical properties can be highly useful in the application of printed electronics.