Fractionation of technical lignins as a tool for improvement of their antioxidant properties

Abstract

a b s t r a c tThe modern biorefinery concept is aimed at the elaboration of sustainable processes with the most profitable utilization of all biomass products obtained at the technological cycle. Lignin separated as byproduct in the lignocellulosic chemical processing is recognized as an important component of polymer systems. The presence of sterically hindered phenolic hydroxyl groups in the lignin macromolecule opens the possibility of its application as antioxidant for composites, e.g. polyurethanes (PU), which are considered as one of the most versatile polymeric materials. In the present work, the object of investigations was lignin obtained as a product, so-called BIOLIGNIN TM , of wheat straw organosolv processing for pulp and fuel ethanol production (CIMV pilot plant, France). However, heterogeneity of the lignin obtained negatively influences its applicability that can be overcome by fractionation. Three soluble fractions were isolated from CIMV lignin by a sequential extraction with dichloromethane (A fraction), methanol (B fraction) and mixture of both the solvents (C fraction) and characterized in terms of their composition, functionality and structure using analytical pyrolysis (Py-GC/MS), 31 P NMR and Size Exclusion Chromatography (SEC) methods. Antioxidant properties of BIOLIGNIN TM fractions were assessed in the tests with free radicals ABTS • + and DPPH • . Application of Py-GC/MS for characterization of the fractions opened an opportunity to found some novel "structure-activity" correlations needed for understanding and tuning of antioxidant properties of lignins. The antioxidant activity of the fractions under investigation was tested by their influence on thermo-oxidative destruction of prepared model PU films. The data of TGA method (oxidative conditions) clearly testified the antioxidant effect of all three fractions with the most prominent activity for C fraction. The shifting of the exothermal maxima connected with oxidizing of volatile products of PU destruction to the higher temperature region by 20-30 K and 30-40 K was registered.

Characterisation of Sequential Solvent Fractionation and Base-catalysed Depolymerisation of Treated Alkali Lignin

“…Previous studies have also reported that lignin dissolved in methanol possesses more methoxyl groups than unfractionated lignin (Li et al 2012;Arshanitsa et al 2013). The relative absorbance of ether bonds at 1120 cm -1 remained nearly the same for OL and F3 in OL, indicating that solvent fractionation did not cleave ether bonds within the lignin molecule.…”

Antioxidant Activity of Organosolv Lignin Degraded Using SO42-/ZrO2 as Catalyst

“…Catalyzed-OL exhibited the lowest IC50 value 145.9 μg/mL, which was less than OL by 18.08%. Some literature on the lignin's antioxidant activity provided evidence that the scavenging activity of lignin on ABTS + radical is mainly due to the electron or proton transfer mechanism (Arshanitsa et al 2013;Aadil et al 2014). The high scavenging activity of Catalyzed-OL for ABTS + • was possibly due to the high phenolic hydroxyl content.…”

Preparation, characterization and the adsorption characteristics of lignin/silica nanocomposites from cellulosic ethanol residue

“…3 It has a large amounts of active groups, such as phenolic hydroxyl and alcoholic hydroxyl, [4][5][6][7] which imparts it chemically reactive activity. 8 It can be used as a potential component for hydrogels, 3 antioxidants, 9 antibacterial agents, 10 sunscreens, 11 solubilizer, stabilizing agents, lubricants, coatings, plasticizers, surfactants, thermosetting polymer composites, thermoplastic polymer composites, lignin-reinforced biodegradable polymer matrix-based composites, rubber composites, foam-based composites and so on.…”