Date of Award
Doctor of Philosophy (PhD)
Mark C. Thies
Scott M. Husson
The use of lignin in the fabrication of soft composites has become an emerging area of research in polymer science and polymer chemistry. These lignin-based materials present numerous benefits, notably, a reduction in the use of petroleum-based precursor, improved structural benefits to otherwise soft host polymers, as well as the inherent antimicrobial and antioxidant properties of lignin, making it suitable for biomaterials. Herein, we present two chemical reaction pathways of incorporating lignin that was fractionated and cleaned using the Aqueous Lignin Purification with Hot Agents (ALPHA) process into poly(vinyl alcohol) (PVA) hydrogel composites for aqueous-based separations. By leveraging the ALPHA process, we can obtain lignins of prescribed molecular weights (MWs) with narrow dispersity (Ð) and low ash content – i.e., low concentrations of sodium and potassium.
In one reaction pathway, lignin was first functionalized with vinyl-containing acrylate groups that enabled free radical chemical crosslinking of lignin chains. Notably, both the lignin MW and chemical functionality had an impact on the permeability of methylene blue (MB), where the breakthrough time of the MB across the membrane was significantly longer for lignin with higher hydroxyl content. Further, the permeability of MB was seen to decrease by over two orders of magnitude with the introduction of just 20 wt % lignin. In addition, the importance of leveraging lignin of narrow Ð in the development of structure–processing–property relationships for these materials was underscored by the consistent, repeatable permeation experiments obtained for these membranes versus their counterparts made with unfractionated lignins.
In the second reaction pathway, both the lignin and PVA chains were chemically crosslinked via a condensation reaction using glutaraldehyde (GA). In general, increases in the GA content and lignin MW resulted in improved mechanical properties, including increases in ultimate tensile strength, storage modulus, and Young’s modulus, which was attributed to a tightening of the hydrated network structure and supported by decreases in equilibrium water uptake and molecular weight between crosslinks. Enhanced mechanical properties were also observed in hydrogel composites containing ALPHA-fractionated lignin as compared to unfractionated, stock lignin, underscoring the impact of the ALPHA process on the resulting properties.
Gregorich, Nicholas, "Elucidating the Mechanical and Transport Properties of Lignin-Based Hydrogel Composites" (2023). All Dissertations. 3309.
Author ORCID Identifier