Sulfo-functionalization of lignin and its impact on the stabilization of colloidal systems
Doctor of Philosophy
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Lignin macromolecules, derived from renewable biomass resources, have gained extensive interest during the past decade as a sustainable substitute for synthetic oil-based materials. The main goal of this dissertation was to formulate and investigate lignin-based materials (dispersants or adsorbents) that are renewable, biodegradable, and non-toxic from the molecular level to the macroscopic level. To obtain desired physicochemical properties, chemical modifications or selfassembly were conducted to alter solubility, size, functionality, and surface energy of products with hydrophobic, hydrophilic, or near neutral wettability. After following various techniques of functionalization, polymerization, and nanoprecipitation (acidification), the desired structure of polymers or particles were formed, which were extensively characterized by implementing various analytical techniques. The correlations between physicochemical properties of unmodified hydrolysis lignin samples and their chemical reactivities toward sulfo-alkylation reactions were evaluated. The fundamental understanding of interactions of lignin derivatives and particles was further evaluated in variable systems (solid films, oil-water systems, and solid suspensions) by evaluating surface and interfacial properties. The formulated (nano) materials were successfully used in different applications including, the adsorption of metal ions, stabilization of emulsions (Pickering/non-Pickering), and the dispersion of clay suspension. The results showed the suitability of the lignin-derived additives in wide-range applications. The results on the material synthesis, physicochemical properties, and their fundamental correlation to their effectiveness in various colloidal systems, can be utilized as guidelines for the development of sustainable processes for the utilization of lignin-based products.