UBC Theses and Dissertations
Toward lignin-based polymeric materials using greener modification methods Liu, Liyang
The urgent necessity for replacing fossil resources has driven researchers to develop more sustainable materials from technical lignin. However, the heterogeneous nature of this complex material must be improved, as industrial feedstocks require a large degree of uniformity. Therefore, the hydroxyethyl modification of lignin was first developed as a platform derivatization method to convert the phenolics and carboxylic acids of industrial lignins into aliphatic hydroxyls. Ethylene carbonate was used as both the reagent and solvent resulting in a variety of hydroxyethyl lignins (HELignins) derived from technical lignin resources. The HELignin derivative was further utilized as a polyol and reacted with diisocyanates to make polyurethane foams. While effective at various substitution levels of polyol, HELignins only had partial solubility in the polyol. As a result, the reaction conditions that led to increased lignin molecular weight and low solubility required optimization to avoid crosslinking. Addressing this issue, an in situ real-time monitoring technique was created to control the quality of the resulting HELignin. An empirical model was built to ensure the reaction could reach near completion without significant by-product formation. The optimized reaction conditions created a HELignin that could be further modified; a catalyst free esterification was developed using organic acid as solvent and reagent. Due to the high selectivity toward aliphatic hydroxyl groups, HElignin which had over 85% aliphatic hydroxyls, showed an advance as a starting material useful for lignin esters with tailored thermal properties based on the organic acid of choice. In one application for an aqueous hydrophobic coating, inspired by the natural suberin compounds, oleic acid was used as a solvent and reagent to esterify the HELignin and subsequently transformed into an aqueous dispersion. These coating materials significantly improved the hydrophobic properties of wood-based products. Critically, the above hydroxyethylation and esterification of lignin satisfied many green chemistry requirements including the adoption of solvent-free reactions, low environment factor (E-factor) reactions, high atom economy, high pot economy, the adoption of low-toxic reagents, and real-time monitoring. Overall, the reaction of lignin with ethylene carbonate led to a greener modification route to convert technical lignin into more sustainable feedstock for society.
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