Preparation of thermal-responsive Pickering emulsion by ATRP modified lignin microspheres

Soda lignin or lignosulfonate from paper mills are often directly applied as surfactant for cement dispersion due to the presence of hydrophilic and hydrophobic groups in lignin. They are also applied to Pickering emulsion, but the efficiency is not so good. In this work, we modified lignin by grafting poly(ethylene glycol) methyl ether methacrylate (PEGME), and then the modified-lignin self-assembled into microspheres that was applied to a lignin-based Pickering emulsion with temperature responsiveness. The particle size of modified-lignin microspheres changed with temperature due to the thermoresponsiveness of the grafted polymer, which also subsequently affect the radius of emulsion droplets. The lower critical solution temperature (LCST) of the modified lignin is 50 °C. When temperature changed from 25 °C to 70 °C, the average particle size of lignin microspheres decreased from 159 nm to 141 nm. Further rising temperature caused the lignin microspheres to agglomerate and to break the Pickering emulsion. The prepared Pickering emulsion is good for drug agent loading and stably-releasing. It is found that the cumulative drug release changed from 43.77% to over 80% after 14 hours at 25 °C and over 50 °C. The lignin-based Pickering emulsion have good thermal cycling stability and ionic resistance, which may offer a potential for the drug release.