Alginates loaded with metal ions can provide effective bio-based PIN FRs for textiles, polymers, surface coatings …. Tens of thousands of tonnes of alginates are produced worldwide annually from brown algae, providing relatively low-cost bio-based materials which are not competing with food crops. Alginates are polysaccharides which are non-toxic and are flame retardant with incorporation of metal ions: sodium, calcium, zinc, copper, nickel, manganese, aluminium … Metal alginates can be bonded to fibres and rendered wash-resistant by cross linking, or alginate fibres can be woven into textiles to provide flame retardancy by char formation, as well as reducing toxic smoke emission and preventing flaming drip. Alginates can also be combined with phosphorus (e.g. DOPO), APP, clays, graphite, silanes, as possible FRs for different polymers. They have also been tested as lithium ion battery separators. This review concludes that more research is needed into the FR catalysis effects of different metals in alginates, into improving mechanical performance of alginates (which tend to be brittle) and into cost-effectiveness of application.
“An overview of alginates as flame-retardant materials: Pyrolysis behaviors, flame retardancy, and applications”, Y-J? Xu et al., Carbohydrate Polymers 260 (2021) 117827 https://doi.org/10.1016/j.carbpol.2021.117827