Tunable Pickering emulsions with polymer-grafted lignin nanoparticles (PGLNs)

Area of Science:

• Biopolymer modification and interfacial science.

Background:

• Lignin, an abundant biopolymer, possesses inherent interfacial capabilities but exhibits strong aggregation in aqueous solutions.
• Controlling lignin aggregation is crucial for harnessing its interfacial properties in applications like Pickering emulsions.

Purpose of the Study:

• To synthesize polymer-grafted lignin nanoparticles (PGLNs) using reversible addition-fragmentation chain transfer (RAFT) chemistry.
• To investigate the impact of polymer graft density and solution conditions on PGLN behavior and Pickering emulsion characteristics.
• To explore the correlation between lignin aggregation, interfacial activity, and emulsion stability.

Main Methods:

• Grafting polyacrylamide onto kraft lignin nanoparticles via RAFT polymerization.
• Systematic variation of polymer graft density, ionic strength, and solvent volume fractions.
• Characterization of PGLNs and emulsions using dynamic light scattering, UV-vis spectroscopy, optical microscopy, and tensiometry.

Main Results:

• PGLNs demonstrated tunable aggregation and retained interfacial activity for Pickering emulsion formation.
• Emulsion characteristics (volume fraction, droplet size, interfacial concentration) were significantly influenced by graft density, ionic strength, and solvent ratios.
• Lower polyacrylamide grafting density correlated with higher interfacial activity and lower interfacial tension, attributed to lignin's hydrophobic interactions.

Conclusions:

• Polymer grafting via controlled radical polymerization is effective for creating functional lignin-based nanoparticles.
• The interfacial properties of PGLNs are primarily governed by the native hydrophobic interactions of the lignin core.
• Optimizing polymer-nanoparticle interactions is key to leveraging lignin's intrinsic functions for advanced Pickering emulsion applications.