Molecularly anchored colorants: Towards enhancing PLA packaging composites with multifunctional and sustainable blue hybrid pigments

This study presents the development of novel polylactide (PLA)-based biocomposites incorporating multifunctional blue hybrid pigments derived from a crop-based anthraquinone dye. The pigments were synthesized by covalently anchoring leuco-quinizarin (LQ), a derivative of plant-sourced quinizarin onto various aminosilane-functionalized mineral and lignocellulosic fillers. This molecular hybridization strategy yielded structurally robust and thermally stable pigments, with tunable properties influenced by the nature of the carrier material. The chemical structure and bonding mechanisms of the hybrid colorants were confirmed by TOF-SIMS and solid-state ¹ ³C NMR. Morphological and optical analyses revealed uniform color distribution, enhanced fluorescence, and distinct particle morphologies depending on the filler used. When integrated into PLA matrices, these multifunctional pigments improved thermal stability, reduced flammability, and modulated mechanical and barrier properties. Notably, inorganic fillers such as silica, mica, and hydrotalcite provided superior fire resistance and reduced gas permeability, whereas bamboo fiber-based hybrids showed lower thermal stability but enhanced biodegradability. The hybrid pigments retained fluorescence and color intensity under elevated temperatures and solvent exposure, significantly outperforming the pristine organic dye. This work contributes new insight into the transformation of crop-derived colorants into multifunctional additives for advanced packaging systems. • Novel functional and stable hybrid pigments were synthesized by covalent bonding. • Hybrid colorants exhibited multifunctional action in biodegradable PLA composites. • Hybrid pigments reduced PLA flammability and gas permeability by up to 20 %. • Inorganic support selection tuned PLA biodegradation rate and mechanical behavior.