Self-assembly synthesis of lignin nanoparticles from <i>Oxytenanthera abyssinic</i> using 1,4-dioxane for antibacterial, antioxidant, and sunscreen properties

Lignin, a renewable aromatic polymer found in lignocellulosic biomass, has several potential uses due to its antioxidant, antibacterial, and UV-absorbing qualities. The aim of this work was to extract soda lignin for sunscreen, antioxidant, and antibacterial properties from Oxytenanthera abyssinic (Ethiopian lowland bamboo) stems using an alkaline treatment. A 1, 4-dioxane-based nanoprecipitation technique was then used to create lignin nanoparticles produced from O. abyssinica (OA-LNPs) via a self-assembly process. The extraction procedure was optimized with temperature (23–120°C), time (1–24 hours) and NaOH concentration (5–15%). 1, 4-Dioxane-based nanoprecipitation was used to synthesis OA-LNPs which were then examined using SEM, EDX UV-Vis, FTIR and 1 HNMR for morphology size zeta potential and chemical structure. Antioxidant activity using DPPH assays, sun protection factor (SPF) measurements in commercial lotions and antibacterial testing against Gram-positive ( S. aureus and S . epidermidis ) and Gram-negative ( E. coli and K. pneumoniae ) strains were among the functional evaluations. Up to 294 mg/g of soda lignin were produced by the extraction. OA-LNPs had a spherical shape size ranging from 65 to 135 nm (mean 115 nm) a zeta potential of -30. 1 mV and no sulfur was found. They also retained phenolic and aromatic functionalities. The antioxidant activity of OA-LNPs was 11. 47 µg/mL which was higher than that of soda lignin (131.1 µg/mL). Due to UV absorption by phenolic groups SPF evaluations showed improvements in commercial lotions up to 114.8±1.3 when OA-LNPs were added. Antibacterial testing showed moderate efficacy against the tested strains with inhibition zones ranging from 12.43± 0.90 to 28.8± 1.11 mm. With better bioavailability and multifunctionality than Soda lignin (SL) these results highlight the environmentally friendly valorization of lignin from underutilized biomass and position OA-LNPs as promising candidates for sustainable applications in food packaging cosmetics and biomedicine.