In another study addressing on polylactide (PLA), a macromolecular nitrogen – phosphorus PIN flame retardant was synthesised in a 2-phase, single vessel reaction from THEIC (tris (2-hydroxyethyl) isocyanurate), polyphosphoric acid and melamine.
THEIC is stated to be a non-toxic triazine derivative for which no corrosive gas or toxic by-products are released during production. The resulting product (tris(2-hydroxyethyl) isocyanurate polyphosphate melamine – TPM) was tested in combination with APP (ammonium polyphosphate) as a PIN flame retardant solution for polylactide (PLA). At 25% loading of APP-TPM (1/3 APP, 2/3 TPM) fire performance of PLA was significantly improved: LOI increased from 20% to 37%, peak heat release rate (pHRR) reduced by 2/3 and UL94-V0 (3mm thickness) was achieved without melt dripping. Analysis shows improved thermal stability of PLA with the PIN flame retardant addition and that fire resistance is probably resulting from the generation of a resistant intumescent char layer with combined carbon and phosphorus compounds.
“A THEIC-based polyphosphate melamine intumescent flame retardant and its flame retardancy properties for polylactide”, X. Zhao et al., J. Analytical and Applied Pyrolysis 122 (2016) 24–34 http://dx.doi.org/10.1016/j.jaap.2016.10.029