Modulating the Spontaneous Adsorption of Lignin Nanoparticle at Oil-Water Interfaces

The performance of (nano)particles in the stabilization of Pickering emulsions depends on their physicochemical features. Therefore, synthetic particles are commonly applied in Pickering stabilization, despite the environmental issues their use raises. Recently, lignin nanoparticles (LNPs) derived from industrial side streams have been investigated as biobased alternatives to replace synthetic stabilizers. Having a well-defined surface chemistry, monodisperse morphology, and a unique core-shell composition, LNPs are hypothesized to show diverse functionality and adsorption capacity at the oil-water interface that affects the long-term Pickering emulsion stability. To gain an understanding on the effect of various colloidal parameters, i.e., type of LNP, type of oil-water system, pH, LNP concentration, and ionic strength, on the adsorption LNPs at hexadecane-water and rapeseed oil-water interfaces, a fundamental study using dynamic interfacial tension analysis is performed. Condition optimized for Pickering stabilization is defined and applied for preparing emulsions. Findings indicated that LNPs adsorbed spontaneously at oil-water interfaces, which is a unique trait compared to known particles' adsorption, usually requiring the application of high forces. LNP adsorption at interfaces is affected by conditions of colloidal parameters, with increasing of pH ensuring the greatest LNP adsorption. Emulsions stabilized with LNPs at the optimized pH 8.0 remained stable after subsequent adjustment to pH 5.0.