Rationally designed functionalized black phosphorus nanosheets as new fire hazard suppression material for polylactic acid

The black phosphorus (BP) nanosheets were firstly obtained by the modified lithium ion intercalation method and then functionalized by cetyl-trimethyl ammonium bromide (CTAB). Owing to the electrostatic interactions, the positively charged CTAB was successfully loaded onto the surface of negatively charged exfoliated BP and the BP-CTAB hybrids were finally obtained. It is found that BP-CTAB hybrids exhibits superior promotion effect on fire safety of Polylactic acid (PLA), which can be attributed to its typical layered structure, abundant phosphorus and good dispersion in matrix. Compared with neat PLA, the peak heat release rate (PHRR) of PLA composite with 2 wt% BP-CTAB decreases by 38.8%. Under the same loading of 2 wt%, the PLA/BP-CTAB2.0 shows better flame retardancy than PLA composites with BP or red phosphorus (RP). Moreover, the time to peak heat release rate (TPHRR) of PLA/BP-CTAB2.0 is postponed from 157 to 200 s. Derived from the uniform dispersion of BP-CTAB, the tensile strength of PLA composites are also improved. Meanwhile, the air stability of BP-CTAB in polymer is investigated. It is observed that the Ag1/Ag2 value of BP-CTAB only decreases from 0.57 to 0.54 even after immersion in water for one month, which can be ascribed to the double coating of polymer matrix and CTAB. This work enriches the method of exfoliating BP, and first explores the influence of BP on the flame retardant and mechanical properties of PLA.