Recently, there has been an increasing interest to develop material platforms using biomass feedstock in an attempt to replace petroleum-based chemicals and plastics. Currently, lignin is considered an easily accessible biomass from pulp processing. For material chemistry, valorization of such biomass is an important goal resulting in enhanced sustainability of feedstock. Lignin is a natural polymer containing a large amount of key functional groups, such as phenols and alcohols, which can be utilized to introduce specific functionalities in efficient ways. To create new materials by utilizing such functionalities, we demonstrate a simple but efficient chemical route to incorporate thiol groups in lignosulfonate which can be easily modified in aqueous medium. Quantitative analyses of incorporated thiol groups were conducted using Ellman’s assay, which confirmed that the thiol concentration can be precisely controlled by tuning reaction conditions. Phosphorous nuclear magnetic resonance (<sup>31</sup>P-NMR) spectroscopy studies further showed that aliphatic OH groups were actively involved in the thiol incorporation reaction, while phenolic OH groups were not largely involved in the reaction. We further demonstrated successful hydrogel formation via radical-based thiol-ene “click” chemistry using thiol-lignosulfonate and a water-soluble polymer having an alkene moiety. The mechanical properties and the extent of cross-linking, of the hydrogel, were closely examined using oscillating rheometry to determine if the thiol-ene “click” reaction is chemoselective enough for the formation of lignin-incorporated hydrogels. Finally, due to the antioxidizing functionality of the native phenol groups in lignosulfonate, we evaluated the potential of the synthesized hydrogels as a synthetic extracellular matrix for adult stem cells.

Hydrogel formation using thiol-functionalized lignosulfonate by thiol-ene click reaction

2019 Fall National Meeting

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