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Kraft black liquor-derived lignin nanoparticles for polyhydroxyalkanoates composite films with multifunctional properties
Summary
Scientists made a new biodegradable plastic film by combining a plant-based material called PHA with lignin nanoparticles extracted from paper mill waste. The resulting film blocks nearly all UV light, resists bacteria growth, and fights off cell-damaging compounds—all while being stronger and more water-resistant than plain PHA plastic. This matters because it offers a promising, eco-friendly alternative to petroleum-based plastic packaging, potentially reducing the microplastic pollution that's increasingly found in our food, water, and bodies.
Petroleum-based plastics dominate the packaging industry, yet they cause persistent environmental pollution and microplastic issues, urgently requiring the development of biodegradable substitutes. Despite polyhydroxyalkanoates (PHA) exhibiting excellent biodegradability and biocompatibility, their mechanical strength is insufficient and they lack the reactive functional groups required for high-performance applications, thereby limiting their usage. Herein, multifunctional PHA–lignin nanoparticles (PHA-LNPs) composite films with synergistic enhanced UV-blocking, antioxidant, and antibacterial properties were fabricated using Kraft black liquor as the lignin source. The tensile strength of the PHA-LNPs composite films first increased to a maximum of 20.0 MPa, then declined with further increase of lignin content, attributed to aggregation caused by excessive lignin addition. Notably, all the thermal stability, water resistance, and hydrophobicity of the PHA-based films were remarkably improved after the introduction of LNPs. In particular, its UV blocking capability was significantly strengthened, with the average transmittance of pure PHA films in the UVA, UVB, and UVC regions (86.43%, 75.36%, and 50.03%) dropping drastically, while the transmittance of PHA-LNPs20 composite films was only 0.23%, 0.06%, and 0.06%, respectively. Meanwhile, the radical scavenging activity of the PHA-LNPs composite films was increased to 77%, which was attributed to the abundant phenolic hydroxyl groups in lignin nanoparticles. Moreover, the as-obtained composite films exhibited excellent antibacterial effects against Escherichia coli and Staphylococcus aureus . In summary, this work demonstrates an effective and green strategy for the high-value utilization of Kraft black liquor, while providing a practical route for the preparation of advanced, multifunctional, biodegradable composite films for next-generation sustainable packaging applications.