(576f) Leveraging Cononsolvents to Directly Tune the Network of Poly(vinyl alcohol)–Lignin Soft Composites

Lignin, a biopolymer and byproduct of paper making, has garnered attention as a greener alternative to petroleum-based polymers as it is derived from abundant, renewable feedstocks. As such, the use of lignin in the fabrication of soft composites for various membrane-based applications has recently grown. In this study, the impact of cononsolvent concentration (in this case, dimethyl sulfoxide (DMSO) and water) on the network structure, and thus, the transport and mechanical properties of soft composites consisting of poly(vinyl alcohol) (PVA) and lignin was investigated. Specifically, a range of concentrations of DMSO/H₂O were investigated by varying the mass ratio of the two solvents from 100/0 (w/w) to 60/40 (w/w). Using the “Freeze-Thaw” method, physically crosslinked membranes were synthesized via three freeze thaw cycles, where the lignin concentration was varied between 0 mass % and 60 mass %. Additionally, solutions containing PVA and lignin with high water concentrations experienced rapid gelation due to the cononsolvency effect. To better understand how the various solvent ratios impacted the properties of the soft composites, both the mechanical and transport properties of the hydrogels were characterized. In particular, the hydrated Young’s modulus, equilibrium water uptake, and methylene blue permeability were characterized. To help explain the observed trends in the mechanical and transport properties, direct images of the swollen network structure were captured via scanning electron microscopy. The images from SEM highlighted the hierarchical network structure that can be achieved simply by varying the mass ratio of DMSO to water (i.e., by varying the cononsolvent ratio).