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McMichael, Philip S.

University of British Columbia

As the second most abundant naturally occurring polymer on the planet, lignin is extracted during the pulping and bleaching of many pulp and paper products. Despite millions of tons of lignin being extracted every year, the vast majority of this amorphous, amphiphilic polymer is burned for energy. Lignin’s heterogenous and variable nature make it a challenging material to work with, but production of lignin nanoparticles (LNPs) can valorize lignin by improving its uniformity, miscibility, and functionalization potential. However, existing methods for synthesis of these nanoparticles generally require time-consuming, multi-step processes with specialized laboratory-scale equipment, or require high volumes of toxic organic solvents to produce relatively low volumes of LNPs. Herein, we outline and assess a novel process for synthesis of uniform LNPs, using subcritical water (scH₂O) as a solvent and ambient water as an antisolvent for kraft lignin. This process, assisted by volumes of easily recyclable organic solvent several times lower than previously reported in the literature, synthesizes chemically and morphologically homogenous nanoparticles in high yield. A range of reactor conditions and solvent/water ratios were considered for their efficacy at producing LNPs, and the effect of a kraft lignin pre-fractionation step was assessed for its ability to improve nanoparticle yield. The effects on nanoparticle chemical structure, thermal stability, suspension stability, morphology, and yield were considered for a range of solvent/water ratios. To further highlight the potential for valorization of lignin, we produced sulfonated lignin nanoparticles (NanoSL) via a traditional solvent-antisolvent (SAS) precipitation process and produced thermally and structurally stable polyvinyl alcohol (PVOH)/NanoSL films. These films were assessed for their potential application as proton exchange membranes (PEMs) for redox flow battery (RFB) systems. These membranes demonstrated electrochemical properties comparable to commercially available membranes, and improved structural properties compared with other bio-based membranes, including unmodified sulfonated lignin-based membranes.

Text

2024-10-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86217

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/