Rodolphe Sonnier, C2MA Mines d’Alès, France, outlined different possible routes for developing bio-based PIN flame retardants. Bio-based molecules can have a high oxygen/carbon ratio (so low energy release in fire), functional groups enabling grafting of flame retardant molecules, and an inherent capacity to generate char (carbon content). Examples cited include lignin or phenols, which can be functionalised with phosphorus, but a challenge is stability in processing. Studies have shown effectiveness of ground olive pomace (olive stone pressing waste) to replace pentaerythritol in intumescents, but black coloration is an obstacle. Phytic acid, naturally found in seeds and which has high phosphorus content, offers potential because it can be combined with different metal salts. The economics of bio-based FRs can be improved if they also have another function in the plastic, e.g. as a plasticiser.
See also the book “Towards bio-based flame retardant polymers” (Springer, 2018) https://www.springer.com/us/book/9783319670829