Ti3C2Tx MXene-Synergized Intumescent Flame-Retardant Polylactic Acid Composites: Flame Retardancy, Thermal Behavior, and SBS Toughening

Polylactic acid (PLA) is derived from renewable resources and can be composted under controlled industrial conditions, but its flammability and brittleness limit wider use. This study combined Ti3C2Tx MXene with surface terminations and an intumescent flame retardant (IFR) system based on ammonium polyphosphate and pentaerythritol (4:1, w/w). A styrene–butadiene–styrene (SBS) elastomer was then added to improve toughness. At a total flame retardant loading of 10 wt%, PLA/8.5IFR/1.5MXene reached a limiting oxygen index (LOI) of 30.32% and a UL-94 V-0 rating without dripping. Compared with PLA/10IFR, the peak heat release rate (PHRR) and total heat release (THR) decreased by 18.6% and 28.8%, respectively, and the residue at 600 °C increased from 5.88 to 6.75 wt%. The composite containing MXene formed a denser char and showed a slightly lower Raman D/G intensity ratio. Adding 10 wt% SBS increased notched impact strength by 48% for PLA/IFR and 31% for PLA/IFR/MXene, but reduced tensile strength and modulus. MXene therefore improved the barrier in the condensed phase at a lower IFR content, while SBS partly recovered toughness.