Investigating the network structure and transport properties of physically-crosslinked lignin-based composites

The biodegradability, antimicrobial properties, and chemical activity of lignin make it attractive for use in the fabrication of sustainable materials. However, the heterogenous nature of lignin has created a bottleneck in understanding how lignin concentration and molecular weight (MW) alter 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) composites, via the freeze-thaw method, using both raw lignins with high dispersity, as well as fractionated lignins with prescribed MWs and low dispersity. Specifically, the lignin concentration and MW were systematically varied, ranging in lignin concentrations of 20 wt% to 60 wt% and lignin MWs ranging from ~5700 g/mol to ~19900 g/mol. The transport properties of these membranes were examined by probing the water uptake and permeabilities of model penetrants (e.g., methylene blue). Furthermore, the Young’s modulus, as well as the complex modulus were characterized via mechanical indentation and dynamic mechanical analysis, respectively. Moreover, lignin leaching was analyzed using UV-vis spectroscopy. Preliminary data indicates that the concentration, MW, and dispersity of lignin modulates the transport and mechanical properties of the soft composites.