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Polyurea (PU) elastomers have become increasingly popular in recent years due to their exceptional blast mitigation, ballistic protection, and wear resistance properties. However, their applications as protective materials are often limited as a result of their high flammability. In this study, aromatic dianhydrides (ArDAs) were employed to capture the thermal decomposing products of PU during combustion and facilitate the generation of highly heat-resistant aromatic polyimides (i.e., end group capturing effect), thus enhancing the material's char-forming ability and improving its flame retardancy. The ArDAs were found to significantly reduce the peak heat release rate (PHRR), total heat release (THR), total smoke release (TSR), and total CO release (TCO) of PU, and meanwhile increased the amount of char residue. At 20 wt% content of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), PHRR, THR, TSR and TCO of PU were reduced by 70.6%, 32.5%, 44.7% and 58.8%, respectively, the char residue was increased by 405%, and the mechanical properties of PU were well maintained (88.5% tensile strength and 91.0% elongation at break of pure PU). These findings demonstrate that ArDAs could serve as a new kind of halogen/phosphorus-free flame retardant for PU elastomers. [Display omitted] • Novel halogen/phosphorus-free flame retardants were designed for PU elastomers. • The flame retardant mechanism is end group capturing by aromatic dianhydrides (ArDAs). • PHRR, THR, TSR and TCO were simultaneously reduced, and char residue was improved. • Both excellent flame retardant property and high mechanical property were achieved. [ABSTRACT FROM AUTHOR]

This work reports our recent effort on the preparation of α-Phenyl-N-(2-propyl-2-hydroxymethyl-1, 3-dihydroxy)-imine-Nickel (Ⅱ) (Ni-MOF) containing polyhydroxy groups and its application in improving the fire performance of PLA composites in combination with ammonium polyphosphate (APP). The flame retardant evaluation revealed that the presence of 1.7% Ni-MOF and 3.3% APP in PLA increased the LOI value to 31.0%, upgraded the UL-94 level to V-0, decreased the peak heat release rate (pHRR), total heat release (THR) and total smoking production (TSP) by 27%, 19% and 50%, respectively, and substantially delayed the time to ignition (TTI) from 67 to 97 s. It was proposed that the flame retardants take effect in both vapor and condensed phases, and Ni-MOF nanosheets can synergistically improve the flame resistance of PLA with APP. The incorporation of Ni-MOF effectively inhibited the deterioration of mechanical properties for PLA composites caused by the presence of APP. • The Ni-MOF nanosheets containing polyhydroxy groups was prepared. • APP and Ni-MOF nanosheets significantly improved the fire safety of PLA composite. • The possible synergistic flame-retardant mechanism of Ni-MOF and APP was proposed. • Ni-MOF effectively improved the mechanical properties of PLA composites. [ABSTRACT FROM AUTHOR]