Abstract
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.