Alkylated Lignin/HDPE Composites With Enhanced Photoaging Resistance, Antioxidant Activity, and Mechanical Properties

High-density polyethylene (HDPE) undergoes significant degradation and aging during prolonged exposure to ultraviolet radiation and oxidative environments, leading to a pronounced decline in performance. However, developing efficient and sustainable stabilization strategies to enhance the photostability of HDPE remains a major challenge. To address this issue, alkylated lignin (AL) was synthesized via chemical modification as a functional filler to improve compatibility with the nonpolar HDPE matrix, thereby maximizing the intrinsic anti-aging potential of lignin. The results revealed that at an AL content of 5 wt%, the HDPE-AL5 composite exhibited optimal tensile strength and elongation at break, even slightly outperforming neat HDPE. Oxidation induction time (OIT) analysis indicated that the OIT of HDPE-AL5 extended from 32.46 to 50.93 min, significantly outperforming neat HDPE. Ultraviolet – visible spectroscopy confirmed that the HDPE-AL composites nearly completely provided UV shielding throughout the entire ultraviolet spectrum. After 5 days of irradiation under a xenon lamp, the elongation at break of neat HDPE decreased to 8.77%, whereas HDPE-AL5 maintained nearly 100% of its original mechanical properties. In summary, the HDPE-AL5 composite preserves inherent mechanical strength while enhancing UV-shielding and antioxidant capabilities. This approach offers a promising route for developing sustainable, high-performance polyethylene materials suitable for outdoor applications. Highlights Alkylated lignin (AL) exhibits excellent interfacial bonding strength with HDPE. The HDPE-AL5 composite retains the original mechanical properties of HDPE. AL endows HDPE with excellent oxidation and UV resistance. After xenon-lamp aging, HDPE-AL5 retains excellent mechanical properties.