Limiting oxygen index (LOI) is one of the important indicators to characterize the combustion performance of polymers. LOI refers to the volume fraction concentration of oxygen in a mixture of oxygen and nitrogen when it is just able to support its combustion. In general, polymers with LOI greater than 27% can be considered flame retardant polymers.^[43] The results (Table 1 ) show that DABPPI has an LOI of 40.9% and is a good flame retardant polymer. MMT-PI has an even higher LOI of 67.9%. It can be observed that the addition of MMT exhibits better performance on the flame retardant behavior of the developed bioinspired composites. Together, MMT and PI built a “wall” in the composite, preventing gas from entering and exiting. This “wall” had a good oxygen barrier, making it difficult for combustion-supporting gas to enter the interior of the material. Likewise, the combustible gas thermally decomposed inside was hard to release to the outside to maintain combustion. Benefiting from the strong interaction between MMT and PI, the composite presented a nearly perfect “brick-and-mortar” structure, and the LOI was greatly improved.

DABPPI burned quickly after being ignited in the LOI test, and its film frame burned out after the test (Fig. S3 in Supporting Information). Whereas, after combustion, MMT-PI still retained its basic framework due to its good flame retardancy. This means that if it is applied in fireproof coatings, like exterior wall coatings, it may further delay the damage to the wall, thus giving people more time to escape.