Rice husk derived lignin particles generated through solvent and pH shifting for Pickering emulsion applications

Pickering emulsions, stabilized by solid particles, offer a sustainable alternative to traditional surfactant-based emulsions, providing advantages in terms of biocompatibility and environmental safety. This study investigates the synthesis of lignin particles (LPs) derived from rice husk, an agricultural biomass waste, using solvent and pH shifting methods. The primary aim was to evaluate how different synthesis methods influence the structural properties of LPs and their performance as stabilizers for oil-in-water Pickering emulsions. LPs were synthesized through solvent shifting (using acetone, ethanol, and tetrahydrofuran) and pH shifting (at pH 4, 6, and 8) methods, and their particle size, surface charge, morphology, and emulsification performance were assessed. Solvent-shifted LPs synthesized with acetone and ethanol exhibited smaller particle sizes and more spherical shapes compared to pH-shifted LPs. The higher solubility of lignin in acetone and ethanol facilitated more controlled precipitation, resulting in smaller and better-dispersed particles. These solvent-shifted LPs also showed enhanced hydrophilicity and negative zeta potentials, improving emulsion stability by ensuring better particle adsorption at the oil-water interface. In contrast, pH-shifted LPs synthesized at lower pH (4 and 6) formed larger and more irregular particles due to rapid precipitation and reduced electrostatic repulsion at lower pH. Despite the larger size and aggregation, pH-shifted LPs demonstrated superior rheological properties, such as higher viscosity and storage modulus, indicating more stable, elastic emulsions. This study demonstrates that synthetic conditions are crucial in tailoring LP properties for enhanced emulsion stability, offering valuable insights for designing functional biomass derived lignin materials for food, cosmetic, and pharmaceutical applications. • Lignin particles (LP) synthesis using solvent and pH-shifting for emulsion stabilization. • Solvent-shifted LPs were more defined spheres compared to pH-shifted LPs. • Lower pH resulted in larger, more hydrophobic LPs that enhanced emulsion stability. • LP synthesis with ethanol and acetone improved emulsion stability.