Characterizing Network Structure in Lignin-Based Hydrogel Composites for Aqueous Separations

Lignin-based hydrogels have garnered attention for use in a variety of aqueous separations as lignin is a sustainable, naturally abundant biopolymer with a high concentration of hydroxyl groups, which can be utilized as crosslinking sites during hydrogel fabrication. However, to date, widespread use of these materials is hindered by our limited understanding of how the addition of lignin alters the network structure of these composite hydrogels. Herein, lignin–poly(vinyl alcohol) (PVA) composites were synthesized using lignins of prescribed molecular weights (MWs) and low dispersity using two different crosslinking agents (CLA) – ammonium persulfate and glutaraldehyde . The permeability of various pollutants through the hydrated composites was measured via ultraviolet-visible spectroscopy, where penetrant permeability was found to depend on the MW of lignin and PVA, as well as the concentration of CLA utilized during membrane fabrication. In addition, poroelastic relaxation indentation was used to characterize both the mechanical and transport properties of the composites. Results from this work indicate that transport of pollutants through the composite hydrogels is governed by a combination of the network structure and strength of interaction between the pollutant and lignin.