Abstract

Lignin possesses several valuable characteristics, including biodegradability, antimicrobial properties, and chemical activity, that make it attractive for use in the fabrication of sustainable materials. However, the heterogenous nature of lignin has created a bottleneck in our understanding of how the introduction of lignin alters the network structure and ultimately the mechanical and transport properties of these soft composites. To address this issue, we have fabricated a series of lignin–poly(vinyl alcohol) (PVA) composite hydrogels using both crude bulk lignins (CBLs; raw lignin with high dispersity) and ultraclean lignins (UCLs; fractionated lignins with prescribed molecular weights and low dispersity). The soft composites were synthesized via the ‘Freeze-Thaw’ method, whereby physical crosslinks between PVA chains are created. Specifically, the lignin concentration and molecular weight were systematically varied, ranging in lignin concentrations of 20 wt% to 60 wt% and lignin molecular weights of approximately 1250 g/mol to approximately 4200 g/mol. To investigate the transport properties of these membranes, both the water uptake and permeabilities of model penetrants, such as methylene blue and bovine serum albumin were examined[EMD1] . Furthermore, to comprehensively probe the mechanical properties of the hydrogels, the Young’s modulus, shear modulus, as well as the loss and storage were characterized via mechanical indentation and dynamic mechanical analysis. Moreover, leaching of lignin from the lignin composite hydrogels were analyzed using UV-vis spectroscopy. Finally, the antimicrobial properties of the lignin-based soft composites were explored by culturing E.coli and Candida strains and counting the colonies of bacterial growth. Preliminary data indicates that the concentration, molecular weight, and dispersity of lignin modulates the degree of crosslinking, swelling, and mechanical properties of the soft composites.