Flame-Retardant Modification of Layered Double Hydroxides from Biomass Resources for Polylactic Acid

Layered double hydroxides (LDHs) have attracted more and more attention in the field of flame retardants because of their halogen-free, nontoxic, and excellent smoke suppression properties. However, due to the easy agglomeration and poor compatibility with the polymer matrix, its flame-retardant efficiency was reduced. In this study, a novel flame retardant containing phytic acid-modified LDH (PA-LDH) was prepared for polylactic acid (PLA). The microstructure and properties of PA-LDH were analyzed, and the flame retardancy of PLA composites based on the PA-LDH hybrid system was discussed. The research results indicated that PA-LDH exhibited better dispersion than LDH in PLA, which was favorable for the improvement of its flame retardancy. The PLA composites containing 25 wt % PA-LDH (11.02 wt % phosphorus content) and 8.33 wt % tannic acid (TA) presented 26.9% limiting oxygen index (LOI) value, and its vertical burning grade (UL-94) reached V-0. Furthermore, cone calorimetry results illustrated that compared with pure PLA, its peak heat release rate (PHRR), total heat release rate (THR), and total smoke production (TSP) decreased by 52.1%, 57.9%, and 62.2%, respectively. All of these revealed that PA-modified LDH significantly improved the fire safety of the PLA matrix by increasing barrier effects and catalytic carbonization effects during the combustion process. Moreover, the addition of PA-LDH could increase the crystallinity (X _c) and mechanical properties in comparison with the PLA/LDH composite, due to the production of more hydrogen bonds of PA-LDH with PLA.