Controlling stabilization of oil-in-water emulsions with lignins through fractionation, functionalization, and formulation

Lignins, heterogeneous assemblies of polyphenolic oligomers present in lignocellulosic plant biomass, are valorized mainly by combustion because of their low solubility in commonly used solvents. However, in addition to antioxidant, anti-UV and antimicrobial properties, and marked interfacial properties are part of lignins physicochemical properties, thus making them good candidates for sustainable colloids. It is hypothesized that lignins solubility and emulsifying performances could be modulated by fractionation, functionalization, and formulation strategies. The importance of the solvent, and of the pH on lignins solubilization in aqueous phase was investigated. Accordingly, simple O/W emulsions stabilized by different lignins were designed and characterized. The whole results demonstrated that lignins solubility in water can be optimized using appropriate co-solvent and pH readjustment resulting in a homogeneous dispersion with only 7.2 +/- 1.8% wt/wt of insoluble lignins. Both fractionation and biocatalytic modification of lignins allowed increasing stabilization of the oil-water interface by limiting coalescence (23%-24% of relative increase of the D90) compared with non-fractionated lignins (32%), thus advocating their potential use as multifunctional emulsion stabilizers. As a result, a direct link between the molar mass profile of lignins and their ability to stabilize the oil-water interface as well as to reduce emulsion's sedimentation could be established. image