Novel lignin-based ionic liquid with APP toward fire safety PLA with well-balanced comprehensive performance

Developing polylactic acid (PLA) composite materials with high flame-retardant properties is of great significance for expanding the applications of these composites. To achieve this goal, a novel lignin-based ionic liquid (Lig-IL) was prepared from lignin,1,3-propanediamine, 2,3-epoxypropyl-trimethylammonium chloride and sodium fluoroborate. The structure of the resulting compound was characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS). Lig-IL was combined with ammonium polyphosphate (APP) to fabricate flame-retardant PLA composites (PLA/Lig-IL/APP), systematic tests were conducted on their thermal stability, mechanical properties, and flame retardancy. Compared with pure PLA, the PLA composites with 0.25 % Lig-IL and 0.25 % APP achieved limiting oxygen index (LOI) of 34 % and a vertical burning grade of UL-94 V-0. Furthermore, the peak heat release rate (PHRR) and total heat release (THR) were decreased to 390.2 kW/m 2 and 50.9 MJ/m 2 , respectively. Besides, low dosage of Lig-IL/APP has tiny impact on mechanical property of PLA composites, showing great potential applications in packaging and electric industry in the coming times. • A new type of lignin-based ionic (Lig-IL) liquid was prepared. • The incorporation of merely 0.5 wt% of Lig-IL/APP can result in outstanding fire retardancy for PLA. • The addition of flame retardants exerts a relatively minor influence on the mechanical properties of composite materials.