Tyrosine-Thiourea Carbon Dots Embedded in Polyvinyl alcohol Films for Transparent and Flexible UV-Blocking Applications

Abstract

The spoilage and protection of foods during storage under UV light are of utmost importance in current postharvest technologies and processes. In this work, tyrosine-thiourea-based carbon dots (TT-CDs) were synthesized via a hydrothermal process and incorporated into a poly(vinyl alcohol) (PVA) matrix to fabricate TT-CDs@PVA composite films for active food packaging applications. The synthesized TT-CDs exhibited broad UV absorption and excellent photophysical properties. Their structural integrity and functional groups were confirmed through systematic characterization techniques, including UV-vis spectroscopy, FT-IR, HR-TEM, XPS, and XRD. The TEM analysis revealed that TT-CDs had an average diameter of 18 nm and were uniformly dispersed within the PVA matrix. The composite film, referred to as TT-CDs15@PVA, contains 15 mL of TT-CDs solution incorporated into the PVA matrix. It exhibits high transparency and exceptional UV-blocking efficiency, attenuating over 99% of UV-C and UV-B radiation and approximately 90% of UV-A radiation. The film showed improved hydrophobicity, with the water contact angle increasing from 12.1 degrees for pure PVA to 63.3 degrees for TT-CDs15@PVA. They also exhibited enhanced mechanical strength, with tensile strain increasing by up to 112.7% compared to pure PVA (15.8%). In vitro cell viability tests using NIH-3T3 and HeLa cell lines confirmed the nontoxic nature and biocompatibility of the composite films, supporting their safety for food packaging applications. Fresh grapes and strawberries were used as model perishable fruits to evaluate the shelf life extension effect of TT-CDs15@PVA films under continuous UV exposure. Compared to no film (blank), low-density polyethylene (commercial film), and pure PVA film, the TT-CDs15@PVA film significantly extended shelf life, minimized spoilage, and maintained excellent visual appearance for up to 7 days at room temperature. These findings highlight the potential of TT-CDs15@PVA films as UV-blocking, environmentally friendly, and high-performance materials for active food packaging.