Composition–performance relationship of ammonium-phytate flame retardants in bio-HDPE–wood composites

Given the finite nature and overuse of our natural resources, sustainable use is crucial to preserving the foundations of life for the future. In addition to fossil resources, certain metals, and rare earth elements, phosphorus (P) is considered to be a strategic resource. We describe the synthesis of various ammonium salts of phytic acid, a sustainable source of P, as biobased flame retardants (FRs). The performance of the novel ammonium-phytates (AmPs) was tested in wood–polymer-composites (WPCs) based on wood flour and bio-HDPE. The resulting compounds were comprehensively characterized by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94, micro combustion calorimetry (MCC), cone calorimetry and environmental scanning electron microscopy (ESEM). We were able to demonstrate a comparable reaction-to-fire performance for AmP compared to the reference FR ammonium polyphosphate (APP). Based on these results, a rationale for the relationship between composition and performance of AmPs is given.