Colloidal lignin particles for eco-friendly and fully emulsified Pickering emulsions: physical stability and interfacial properties

Colloidal lignin particles (CLPs) are emerging as eco-friendly alternatives to molecular fossil-based emulsifiers, also offering an effective way to incorporate lignin's multifunctionality. In this context, this work aims to demonstrate the role of CLPs in effectively stabilizing Pickering emulsions, thereby expanding the potential use of lignin in high-performance delivery systems, such as cosmetic formulations. For this, softwood kraft lignin CLPs (10–50 g/L) were used to create oil-in-water Pickering emulsions with an oil volume fraction of 0.3–0.7. Optimization was performed by response surface methodology with the emulsified layer (EL) and the emulsion droplet size selected as the objective responses to be maximized and minimized, respectively. The increase in CLPs concentration and oil volume fraction has enhanced the EL magnitude and reduced the oil droplet size, resulting in fully emulsified and stable systems. The optimized formulation was evaluated for storage stability, stabilization mechanism, and rheological behavior. The emulsion exhibited excellent long-term stability, with no significant changes in droplet size, morphology, or homogeneity observed over one month. Confocal microscopy and Cryo-Scanning electron microscopy revealed that CLPs bridged between droplets, resulting in highly efficient packing of oil droplets. Furthermore, the emulsion exhibited a gel-like behavior, which is favorable for applications requiring enhanced stability and ease spreading. Overall, the obtained results provide insights into the formulation of completely emulsified systems using lignin-based stabilizers, highlighting favorable attributes for applications in eco-friendly cosmetic and personal care products. • Colloidal lignin particles (CLPs) are effective, eco-friendly Pickering stabilizers. • CLP concentration and oil fraction rule the formation of fully emulsified systems. • CLPs stabilize emulsions via particle bridging, enabling efficient droplet packing. • Optimized emulsions exhibit long-term stability and gel-like rheological behavior.