The quest for environmentally benign plastics: advances in greener and more sustainable flame retardant formulations

The quest for environmentally benign flame-retardant plastic additives has gained significant attention in recent years due to the harmful environmental effects of conventional flame-retardant additives on human health and the environment. Discussed in this review are the very latest developments in multi-component flame retardants comprising at least one of their elements as a bio-derived phenol, a poly/saccharide derivative, or a greener phosphorus source. Chief among these green additives discussed are tannins, lignin/lignans, alginate, cellulose, starch, chitosan, and phytic acid. The representative studies discussed herein demonstrate the potential of these greener alternatives to enhance the flame retardancy, thermal stability, and smoke suppression properties of various polymers, including polyurethane, polylactic acid, epoxy resin, and polypropylene. A table summarizing key metrics for assessing fire retardancy is provided as a convenient reference. In concluding the review, several future directions and cautionary notes for future work in the field are discussed, including the need to optimize flame-retardant systems, assessing the impact of flame retardant additives on polymer mechanical properties, the practical, technical, and economic factors involved in scaling up production of plastics incorporating green flame-retardant additives, and assessing the long-term environmental impact of such additives.