Investigating lignin self-assembly on its performance as antioxidant nanomaterial

Release and accumulation of greenhouse gases in the atmosphere and non-degradable materials in ecosystems, has created two of the most ill-fame environmental challanges faced to date, i.e., global warming and pollution. Common to both is that they originate from petroleum resources. In order to remediate, alternative sources for energy and fuels alongside industrially relevant building-blocks for materials, needs to be generated from renewable resources in an efficient manner. One way to achieve this is to exploit lignocellulosic biomass. In the present work, lignin, as one of the three major ingredients in biomass, was extracted from beechwood sawdust through organosolv processing. Being the most abundant and renewable polyaromatic compound available, it also carries natural antioxidant activity that can be exploited in a plethora of applications. Yet, the specific antioxidant performance for polymers such as lignin is complex, and does not correlate easily with structural features. Herein, we show how varying the initial organosolv conditions sets prerequisites for the lignin extracts behavior in solution. This is further highlighted by addition of intercalating salts which affect π-π stacking interactions. Subsequently, by affecting the forces dictating macromolecular properties, associated effects are observed on antioxidant activity (DPPH radical scavenging). Additional resolution of the polydisperse lignins were achieved by solvent-based (acetone-water) fractionation to create sub-sets of the initial lignin isolates. The results show that coil expansion enhances the antioxidant activity for lignins with certain chemical characteristics; other lignins described as more condensed remain unchanged in terms of antioxidant activity. These findings contribute not only to QSAR-type explanation of structure-dependent antioxidant behavior, but also gives insight into how the lignin polymer behave in general, easing as such its implementation into other areas of application when it is used as replacement for petroleum-based equivalents.