Simultaneous exfoliation and functionalization of black phosphorus by sucrose-assisted ball milling with NMP intercalating and preparation of flame retardant polyvinyl alcohol film

Recently, layered black phosphorus (BP) has become a rising star in two-dimensional materials because of high thermal stability, excellent mechanical properties, and size effect. Layered BP can be used as an ideal filler for the preparation of polymer-based composites with high performance. Realizing the exfoliation and functionalization of BP has become the key to BP's application. Under the protection of N-methylpyrrolidone (NMP) and the assistance of sucrose, we completed the preparation and functionalization of layered BP by ball milling. Surface grafting of oxygen-containing functional groups can realize the uniform dispersion of BP in matrix and improve its stability in air. As expected, the nanocomposites prepared by adding sucrose grafted BP into polyvinyl alcohol (PVA) matrix have significantly improved flame retardancy and mechanical strength. When the addition amount of BP-sucrose(N) was 5 wt%, compared with pure PVA, the decrease of the peak heat release rate (PHRR) and total heat release (THR) reached 52.5% and 32.8%, and the tensile strength increased by 131.2%. Moreover, the addition of NMP can avoid the excessive destruction of the two-dimensional crystal structure of BP, which can also improve the performance of nanocomposites. Due to the encapsulation effect of sucrose, the nanocomposites have excellent air stability. The Ag1/Ag2 value only decreases from 0.52 to 0.49 even after three months of exposure to environmental conditions, which proves that the degree of oxidation is low. This work has provided an efficient way to exfoliate and functionalize BP simultaneously, and expanded the application of BP in flame retardant nanocomposites.