Alkaline lignin extracted from furfural residues for pH-responsive Pickering emulsions and their recyclable polymerization

Recycling of waste leads to a decrease of environmental pollution and landfill. In this work, we describe an interesting application of furfural residues in fabricating pH-responsive Pickering emulsions and their stable emulsion polymerization. Alkaline lignin extracted from furfural residues is soluble in basic water. However, in acidic conditions, lignin becomes insoluble and particles are formed, which could be used as an effective particular emulsifier for reversible styrene-in-water Pickering emulsions. The emulsions will break when the pH value of the aqueous phase increases. The emulsion system based on a small amount of lignin, 0.05 wt% in water, exhibits good pH-responsivity. Lignin-coated polystyrene (PS) microparticles and pure PS microparticles have been fabricated using the emulsion template. Furthermore, this lignin emulsifier can be recirculated after polymerization. Finally, we propose a cheap and recyclable route for industrial emulsion polymerization. This work opens up new possibilities for agricultural residues as a valuable and recyclable emulsifier in green chemistry.