Polylactic acid/quercetin composite films with enhanced UV-shielding and antioxidant properties for packaging applications

A composite film with synergistic UV-shielding, antioxidant and enhanced mechanical properties. • UV absorption mechanism of quercetin, confirming its intrinsic π→π* and n→π* electronic transitions in the UV region. • A great application potential in sustainable food packaging for mitigating photooxidative degradation of packaged products. With the escalating severity of environmental issues and the surging demand for bio-based alternatives to petroleum-based plastics, polylactic acid (PLA) has garnered extensive attention as a renewable polymer. However, its poor ultraviolet (UV) resistance restricts long-term applications in outdoor scenarios and food packaging-two critical fields requiring prolonged material stability. To address this inherent limitation, quercetin, a natural flavonoid renowned for its exceptional UV absorption and antioxidant properties, was successfully incorporated into PLA via a solution-casting technique for the fabrication of functional UV-shielding films tailored specifically for food packaging applications. Density functional theory (DFT) calculations confirmed quercetin’s superior UV-absorbing capacity via intense π→π* and n→π* transitions (200–400 nm). The composite films exhibited homogeneous surface morphology and high visible transparency, while significantly reducing transmittance at 280 nm (T₂₈₀) to as low as 1.18%. Furthermore, the films retained robust UV-shielding efficiency even after 7 h of continuous UV irradiation, demonstrating excellent photostability. Mechanical analysis showed that moderate quercetin incorporation improved PLA’s tensile strength by mitigating inherent brittleness, while antioxidant assays (DPPH and ABTS) demonstrated over 90% free-radical scavenging efficiency. These findings validate quercetin's synergistic effect in simultaneously enhancing the UV protection and oxidative stability of PLA. Migration tests showed negligible release in 10% ethanol (simulating aqueous foods), but higher release in 50% and 95% ethanol due to enhanced matrix swelling. This controlled release behavior highlights the films' suitability for fresh produce packaging, where minimal migration in high-moisture environments is desired. Collectively, this work presents an efficient strategy to improve the UV resistance of bio-based polymers, advancing their practical utility in active food packaging to mitigate photooxidative degradation. Download: Download high-res image (149KB) Download: Download full-size image