Boron nitride nanosheets with controlled size and thickness for enhancing mechanical properties and atomic oxygen erosion resistance

The comprehensive effects of the dimensions and the thickness of boron nitride nanosheets (BNNSs) on the composite properties are evaluated in this study. BNNSs were directly prepared in cellulose acetate (CA)-acetone solution and separated into different size ranges by multi-step centrifugation, while composite films were then fabricated by employing as-prepared nanosheets as fillers and CA, a biodegradable polymer, as the matrix. Break elongation was significantly increased by filling large BNNSs due to the reduction of bubble defects and the slowdown of the crack propagation. Importantly, the "zipper crack" consists of two ordered and meshing protruding teeth, contributing to high energy absorption and fracture toughness. A large surface area in one plane and high stability of the BNNSs can effectively protect the polymer matrix from atomic oxygen (AO) erosion. Furthermore, the embedment of BNNSs with high aspect ratio can achieve significant enhancement of mechanical properties and AO erosion resistance. All results indicate that the boron nitride sheet is a promising nanofiller for polymeric composites and, more importantly, high aspect ratio is the critical factor for achieving the desired improvement.