A highly efficient route was created to convert technical lignin into esterified lignin derivatives of controlled molar mass allowing the examination of structure-property relationships. The two-step reaction performed using a “one-pot method” involved the hydroxyethyl derivatization of lignin’s phenolic and carboxylic acid groups with ethylene carbonate (serving as solvent and reagent) followed by the direct esterification with an organic acid (serving as the solvent, reagent, and catalyst). The resulting homogeneous mixtures were fractionated by downward precipitation with water to obtain five different lignin fractions. Our results revealed that their conformation, hydrodynamic radius, and glass transition temperature (Tg) are highly dependent on the absolute molar mass of lignin measured with multi-angle light scattering. In solution, 50 - 60% of the obtained lignin derivatives have polymeric characteristics, with a less-compact coil conformation; the resulting Tg of this fraction was around 80 °C. The remaining 30% - 40% of the technical lignin was oligomeric in size with more end group units. Their conformation was close to a solid sphere, indicating a highly compact and branched structure with the corresponding Tg near or below room temperature. The novel and the efficient route provide an in-depth understanding of the differences in structural features amongst different lignin resources that aid in advancing the design and engineering of these abundant renewable materials. The adoption of ethylene carbonate and organic acid as multi-functional solvents and reagents allows integration into the one-pot synthesis route and satisfies many sustainable chemistry requirements. This process delivers a clear path towards the derivitization of kraft lignin into uniform building blocks.

Insight into versatile lignin esters for tailored bioplastics and sustainable materials

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.