Microwave-assisted organosolv extraction for more native-like lignin and its application as a property-enhancing filler in a light processable biobased resin

Abstract

The heterogeneous nature of lignin poses significant obstacles to its practical use in material applications. Common fractionation methods employ harsh processing conditions that further exacerbate lignin's structural complexity. We propose a microwave (MW)-assisted approach for a mild organosolv extraction of structurally-intact lignin from spruce wood. The efficient energy transfer enabled by microwave irradiation facilitates the rapid extraction of lignin in 5, 10, and 20 minutes, ensuring a low level of process severity. Comparison of the 10 minutes MW-extracted lignin products with a cyclic-extracted (CE) organosolv lignin revealed that equivalent amounts of β-O-4 linkages were preserved in both processes. This is indicative of the promising potential of MW-extraction as a biomass pretreatment method for the rapid extraction of more native-like lignin. Finally, we demonstrate the utilization of both MW- and CE-extracted lignins as property-enhancing fillers in a biobased photocurable resin for digital light processing (DLP). The more native-like structures of the mildly-extracted lignins proved beneficial for functionalization with reactive methacrylate moieties, enabling the mechanical reinforcement of DLP 3D printed thermosets with improved toughness after the incorporation of only 1 wt% of the lignins. Compared to the resin without lignin, the tensile strength was improved by 15 and 41% and elongation at break by 79 and 75% in the presence of methacrylated MW- and CE-lignins, respectively. This highlights the potential of MW and CE strategies to effectively process and modify lignin, thereby enhancing its utilization in targeted material applications.