Pickering emulsions produced with kraft lignin colloids destabilized by in situ pH shift: Effect of emulsification energy input and stabilization mechanism

We introduce Kraft lignin colloids produced by destabilization of a kraft lignin solution by pH shift from 2 to 11. The system includes lignin particles and hydrocolloid aggregates in equilibrium (KLP), which are used to control the emulsifying energy and to stabilize oil-in-water emulsions under high energy at pH 11 and 7, yielding excellent stability (at least three months with no creaming). We investigate emulsify technology (ultrasonication and homogenization), energy input (high energy or low energy), particle desorption, drop size, and rheology on the stability of KLP-based Pickering emulsions according to the system's pH. The ultrasonication leads to fine, stable and homogenous lignin emulsions without observing macroscopic creaming phenomenon, whereas homogenization only limits to alkaline condition. Regarding homogenization process, increasing the energy input helps to reduce the emulsion droplet size and consequently improves emulsion stability. In addition, the emulsion produced at acidic conditions always presented excellent stability, independent of the emulsify parameters. Considering the synergistic effects of emulsification protocol, surface activity, and particle interactions, the results indicate the possibility of extending the applications of kraft lignin as a Pickering stabilizer in neutral and alkaline conditions. It also creates a promising method to control the stability and emulsion microstructure in the industrial KLP based emulsion preparation process.