Fabrication of flame retardant toughened PLA base 3D printed materials with modified lignin by phytic acid

Lignin, a natural macromolecule rich in aromatic rings and hydroxyl groups, holds significant promise in environmentally friendly applications. In this study, a lignin-based flame retardant (lignin–diethylenetriamine–phytic acid, P₂N-lig) was synthesized through a Mannich reaction between alkali lignin and diethylenetriamine to introduce nitrogen, followed by phosphorylation with phytic acid to incorporate phosphorus. When P₂N-lig were added into PLA composites (T-PLA) which were toughened by TPU and MMT, the T-PLA/P₂N-lig composites demonstrated enhanced physicochemical and flame-retardant properties. The 9 wt% T-PLA/P₂N-lig formulation exhibited acceptable mechanical performance alongside significantly improved thermal stability and fire resistance, achieving a 39.27% reduction in peak heat release rate (pHRR), a 22.88% decrease in total heat release (THR), and a UL-94 V-0 rating. Further evaluation of 3D-printed specimens revealed that the 6 wt% P₂N-lig formulation achieved a limiting oxygen index (LOI) >24%, a UL-94 V-2 classification, and minimal mechanical degradation, demonstrating suitability for 3D printing applications.