Bio-derived tannic acid-Eu(iii) coordination synergizes with aluminum diethylphosphinate for low-loading and high-efficiency flame retardancy in PA66

Abstract

A bio-derived europium–tannic acid complex (Eu@TA) was synthesized via a facile aqueous coordination strategy, leveraging the polyphenolic structure of tannic acid as a multidentate ligand and europium ions (Eu³⁺) as the coordination center. This hybrid complex was melt-blended with aluminum diethylphosphinate (ADP) into a polyamide 66 (PA66) matrix to develop a synergistic low-loading flame-retardant system aimed at preserving the mechanical integrity of the pristine resin. With 8 wt% ADP and 2 wt% Eu@TA, the material reached a limiting oxygen index of 32.5% and achieved a UL-94 V-0 rating, and the peak heat release rate (PHRR) decreased to 318 kW m⁻² with an increased fire performance index (FPI). Thermal analysis in air showed that the composite formed a stable carbonized layer at elevated temperatures, and the coordinated polyphenolic network favored a more compact char structure. Gas phase analysis further indicated that the system released fewer combustible volatiles during decomposition. The material retained about 97.6% of the tensile strength and about 87.8% of the impact strength of the neat sample, reflecting a largely preserved mechanical response. Because tannic acid has long been used in biological macromolecule modification and biointerfaces, the Eu@TA approach provides a bio-derived option that can be extended to polymer systems requiring both fire resistance and compatibility with biopolymer components.