Günter Beyer, Fire and Polymers Belgium, summarised possibilities of bio-sourced flame retardants, Phytic acid (inositol hexaphosphoric acid), the natural phosphorus storage molecule in plants (especially in seeds), with up to 28% P by weight, has been demonstrated to be an effective flame retardant, and is readily available. The FR efficiency of MDH (magnesium di hydrate) can be improved by a coating with the zinc-salt of phytic acid (Meng 2019). DNA (genetic material) is also available (e.g. in fish processing wastes), and contains phosphorus, nitrogen and natural sugar groups. It has been tested as a surface treatment of EVA (Alongi 2014). Tannic acid or lignin, both natural carbon-containing molecules, are sometimes presented as flame retardants, or they can be modified or functionalised (e.g. by phosphorylation), but in some cases the research does this by using complex, synthetic organic chemicals (Lang 2015, Prieur 2016).
See also Hobbs 2019 review in pinfa Newsletter n°103.