Recent Advances in Biomass-Based Flame-Retardant Poly(vinyl alcohol) Composites

Poly(vinyl alcohol) (PVA) is widely used in films, fibers, hydrogels, aerogels, coatings, and adhesives because of its superior transparency, biocompatibility and chemical versatility. Its inherent flammability and potential melt dripping, however, restrict applications that require reliable fire safety. Biomass-derived flame retardants offer a promising route to PVA composites because their hydroxyl, amino and phosphate structures can promote carbonization, release noncombustible gases, scavenge flame-propagating radicals, and reinforce condensed-phase barriers. This review summarizes recent advances in flame-retardant PVA composites based on cellulose, chitosan, lignin, phytic acid, tannic acid, sodium alginate, cyclodextrin, amino acids, and related bio-based components. Their flame-retardant mechanisms, modification strategies, and interactions with inorganic nanomaterials are discussed with emphasis on associated property trade-offs. Current evidence indicates that unmodified biomass components often exhibit insufficient flame-retardant efficiency, limited thermal stability, weak char integrity, and moisture sensitivity when used alone. Phosphorylation, ionic complexation, multiple crosslinking and catalytic carbonization can substantially improve their effectiveness while enabling thermal management, ultraviolet protection, antibacterial activity, hydrophobicity, self-healing, and fire-warning functions. Nevertheless, loss of toughness or transparency, additive leaching and limited long-term validation remain important barriers. Future development should focus on integrated robust interfacial design, durable multifunctionality, scalable processing and application-relevant fire and environmental assessment.