Elucidating the Network Structure and Transport Properties of Lignin-Poly(vinyl alcohol) Composites Hydrogels Containing Fractionated Lignins

Lignin-containing hydrogels have garnered attention for use in a variety of aqueous-based separations as lignin is an abundant biopolymer with a high concentration of hydroxyl groups which can be utilized as crosslinking sites during hydrogel fabrication. However, to date, little is understood regarding how the addition of lignins alters the network structure of these composite hydrogels. Herein, a novel series of lignin–poly(vinyl alcohol) (PVA) composite hydrogels were synthesized utilizing ultraclean lignins (UCLs) of well-defined molecular weights (MWs) and low dispersity. The UCLs were obtained via fractionation of crude bulk lignins. The network structures of the hydrated composites were characterized via small angle neutron scattering where a Modified Lorentzian Power Law model was used to obtain correlation lengths for the composite hydrogels. The permeability of various pollutants (e.g., methylene blue, bovine serum albumin) through the hydrated composites was measured via ultraviolet-visible spectroscopy, where penetrant permeability was dependent on the MW of both the lignins and PVA, and the concentration of crosslinking agents utilized during membrane fabrication. In addition, mechanical indentation was used to characterize Young’s modulus of the hydrogel composites.