Sustainable fire-retardant PLA/PBAT blends enhanced with carbon dots, fly ash, and hydrothermal liquefaction-derived hydrochar for interior design and furniture components

The growing demand for sustainable materials has accelerated the development of bio-based polymers such as polylactic acid (PLA). Although PLA combines biocompatibility, high mechanical strength, and renewable sourcing, its intrinsic brittleness, low elongation at break, and limited crystallinity restrict its use in durable and fire-sensitive applications. Blending PLA with poly(butylene adipate-co-terephthalate) (PBAT) is a widely adopted strategy to enhance toughness; however, poor interfacial adhesion and high flammability, often accompanied by severe melt dripping, still hinder broader implementation. Some halogen-based flame retardants are restricted due to environmental and health concerns, promoting the search for eco-friendly alternatives such as phosphorus- and carbon-based systems. In this context, the present work explores a sustainable approach for improving the performance of a PLA/PBAT 80/20 w/w blend through the incorporation of carbon dots (CDs) derived from rosin via pyrolytic decomposition. Rosin, a by-product of wood processing obtained from tree exudates, represents a renewable and low-cost carbon source. The prepared PLA/PBAT blends, manufactured by batch mixing, were modified with different CD loadings to investigate their role as multifunctional modifiers. The influence of CDs on morphology, viscoelastic behaviour, thermal stability, and mechanical performance was systematically evaluated. Moreover, the study considers the broader perspective of integrating waste-derived fillers, such as hydrothermal liquefaction hydrochar from tannery sludge and fly ash, as complementary sustainable additives to further tailor mechanical, fire, and aesthetic properties for semi-structural and design-oriented applications. Particular attention was devoted to their potential synergistic action, together with CDs and two conventional flame retardants (i.e., phytic acid and magnesium hydroxide), in promoting char formation, reducing heat release, and mitigating melt dripping during combustion (see Fig. 1). The results highlight the potential of CDs and industrial-derived wastes as eco-friendly reinforcing and flame retardant agents for PLA/PBAT systems, contributing to the development of safer, high-performance biodegradable composites aligned with circular economy principles and new decoration design.