A polyphosphoramide-grafted lignin enabled thermostable and fire-retardant polylactide with preserved mechanical properties

It has been desirable to create biodegradable polymer materials that are thermally stable, flame- retardant and mechanically robust. One promising strategy is to develop fire retardant polylactide (PLA) using lignin as inexpensive fillers, but existing functionalized lignin cannot improve the thermal stability of PLA, in addition to unsatisfactory fire retardancy. Herein, we report a lignin-derived fire retardant (LF) by grafting polyphosphoramide into the chemical structure of lignin waste through graft polymerization. The results show that with 8 wt% of LF, the final PLA shows significantly enhanced thermal stability in N 2 . Moreover, the resulting PLA achieves a satisfactory UL-94 V-0 rating, meeting the demanding requirement of fire retardancy in industries. Additionally, the PLA/LF composite displays increased elastic modulus and well-preserved strength and ductility of pure PLA. This work provides an effective strategy for creating biobased fire retardant additives using industrial lignin waste, and PLA biocomposites which hold great promise for packaging, fabrics, electronic, and automotive applications.