Biomolecules as green flame retardants: Recent progress, challenges, and opportunities

Numerous flame retardants (FRs) have been researched since the 1900s to improve the fire-resistance performance of materials used in construction, industrial production, and daily life, which have developed significantly over the past 25 years. Especially, biomolecules have recently attracted significant attention as green flame retardants (FRs) owing to their low environmental and general toxicological impacts and rapidly decreasing cost. In particular, many flame-retardant biomolecules can promote char formation by swelling upon heating owing to their abundant carbon-, phosphorus-, and nitrogen-containing functional groups. In this review, we focus on several types of biomolecules that have been applied as FRs. We classify most of the biomolecules reported in FR applications to date, such as carbohydrate- and biomass-derived molecules, proteins, DNA, phytic acid, and ATP. In addition, we describe and summarize the unique properties of these materials that make them suitable for use as FRs. Furthermore, we discussed the past and present status of biomolecular FRs and interpreted some of the challenges that need to be addressed in order for biomolecules to be widely used as next-generation FRs. We believe that this review will promote the research and development of the next-generation FRs having environmental and biological compatibility.