Sequential Multiaxial Stretching-Engineered Polyhydroxyalkanoates/Graphene Quantum Dot Composites: Synergistic Enhancement of Mechanical Robustness, Long-Term Stability, and Multifunctionality for Sustainable Materials.

Polyhydroxyalkanoates (PHAs), despite their biodegradability and compostability, face limitations in practical applications due to insufficient mechanical strength, poor storage stability, and lack of functionality. A melt-blending and solid-phase sequential multiaxial stretching strategy to synergistically address these challenges by incorporating graphene quantum dots (GQDs) as multifunctional nanofillers is proposed. During melt processing, GQDs achieve uniform dispersion within the PHA matrix, while the sequential stretching protocol facilitates the transformation of interlamellar tie molecules from α to β-form crystal. This structural evolution enhances crystallinity, molecular orientation, and rigid amorphous fraction, yielding a tenfold increase in tensile strength (from 18.2 to 190.5 MPa) while retaining high elongation at break (70%). The optimized PHAs/GQDs composites demonstrate exceptional storage stability, retaining tensile strength at 147.9 MPa and elongation at break at 57%, respectively, after 30-day aging. Notably, the incorporation of 2 wt.% GQDs imparts robust antimicrobial performance (bacterial adhesion <0.4 × 10⁵ CFU mL), UV-shielding capability (>90% for UVB), and fluorescence stability. This scalable manufacturing approach establishes a foundation for developing high-performance PHA-based materials in sustainable packaging applications.