Book chapter looks at metal and organic compounds which generate char or cross-linking in fire … so in fact: PIN FRs! The chapter on non-conventional approaches in the FR Polymers Handbook (see above) considers three PIN flame retardancy approaches. It proposes metal ions which can promote char formation, which is the mechanism used by many mineral PIN FRs and synergists today. Also discussed are metal ions delivered in organic structures, which can also contribute to char formation, covering calcium, aluminium, copper, zinc, barium, zirconium and other metals, with the example of inclusion in natural alginate. Organic compounds which can contribute to polymer cross-linking (by hydrogen bonding, stacking, end-group capture) or polymer rearrangement-based char formation during combustion are discussed, including phenylacetylene, phenylmaleimide, phenylates, deoxybensoins, and N-containing organic compounds: azobenzenes, aromatic Schiff bases, triazoles. Combination of these approaches with conventional PIN FRs is discussed.
“Flame retardants without conventional flame-retardant elements” chapter 15 (22 pages) in Fire Retardancy of Polymeric Materials, 3rd edition, B-W. Liu & Y-Z. Wang 2024 http://dx.doi.org/10.1201/9781003380689-15