Layer-over-Layer Electrostatic Self-Assembly of Bioresourced Compounds in Thermoreversible Polylactide Gels as an Effective Approach to Enhance the Flame Retardancy of Aerogels

Polylactide is a high potential polymer that can satisfy the growing demand for sustainable and lightweight materials in construction, packaging, and structural applications. However, their high flammability poses a serious concern. Herein, with the aid of solvent exchange and noncovalent interactions, poly(l-lactide) (PLLA) thermoreversible gel was modified with sodium alginate (SA), chitosan (CS), and phytic acid (PA) via a layer-over-layer approach. Freeze-drying of the modified hydrogel furnished a highly flame retardant aerogel with shape stability and no shrinkage. The modified PLLA aerogel (PLLA@SA@CS@PA) exhibited self-extinguishment of flame, the highest limiting oxygen index of any porous polylactide (∼32%), and a tremendous reduction in flammability parameters such as the heat release rate, heat release capacity, total heat release, etc. A comprehensive mechanism of flame retardancy was proposed. This work provides a sustainable strategy for the flame retardant modification of semicrystalline polymer-based aerogels and is expected to expand their practical applications in various industrial sectors.