The dynamic method for monitoring ionisation of the lignin functional groups in a 0.1 N NaOH solution at ambient temperature by means of the SEC technique with multiwave UV detection was performed. An increase in absorbance at 210, 278, 304, 320 and 350 nm was examined to reveal the ionisation dynamics in respect to functional groups’ acidity; that is, carboxyl groups, carbonyl- and double-bond conjugated phenol hydroxyls. A distinctive response of absorbance at 210 and 278 nm on the ionisation of carbonyl- and double-bond-conjugated phenols was found. Simultaneous characterisation of lignin by molecular weight (MW) and chemical heterogeneity was performed. A non-uniform distribution of reactive sites over the MW distribution for commercial kraft lignin (Curan) was found employing the family of chemical composition distribution curves. The redistribution of extended chromophore structures over time along the lignin’s MW distribution causes a misrepresentation of the UV chromatogram pattern and influences the accuracy of MW values.
The antioxidant activities (AoAs) of 50 different technical lignins have been determined. The lignins of various botanical origins (annual plants, coniferous trees, and deciduous trees) were isolated and fractionated by different techniques (delignification by alkali, kraft process, fast pyrolysis, and hydrolysis). The structure and the functionality of lignins were characterized by functional group analyses (phenolic OH, carboxyl, and methoxyl groups), analytical pyrolysis pyrolysis/gas chromatography/mass spectrometry/flame ionization detector (Py-GC/MS/FID), electron paramagnetic resonance, size exclusion chromatography, and titrimetric methods, and the AoAs were evaluated as the capacity to scavenge the DPPH· and ABTS·+ free radicals. The relationship between the lignin structure and the AoA was characterized by pair correlation, partial correlation, and multivariate regression analyses, including correlated components regression. The results were compared with those of lignin model compounds and low molecular weight phenylpropanoids. It has been shown that molecular weight does not influence essentially the AoA of lignins. There is a relationship between the activities of low and high molecular weight polyphenols; their mechanisms of action are also similar. The structure-related AoA of lignins has been quantified for the first time.
The oxidative modification of Biolignin (BL) has been investigated to make it more suitable as an adsorbent for transition/heavy metals. BL is a by-product of a wheat straw organosolv process for the production of pulp, ethanol, and pentoses (CIMV S.A. pilot plant, Levallois Perret, France). It was subjected to oxidation by a polyoxometalate (POM) H3[PMo12O40], aiming at the increment of oxygen-containing adsorption-active sites. The POM oxidation of BL was performed under moderate conditions (1 bar, 60–90°C, and 200°C) with the co-oxidants O2 or H2O2. The resulting lignin functionality and structure was evaluated by pyrolysis-gas chromatography/mass spectrometry, solid-state 13C nuclear magnetic resonance, Fourier transform infrared, and chemical analysis. The condensation degree of BL and its COOH and aliphatic OH group contents increased significantly, whereas the polymer structure was maintained. Under optimal conditions with POM/H2O2, the sorption capacity of lignins toward Cd(II) and Pb(II) was increased threefold and twofold, respectively.
The thermocatalytical synthesis conditions required for the activation of wood charcoal with NaOH in terms of the formation of pores in its structure were investigated. The present study was conducted to explore the potential application of activated carbons as electrodes in supercapacitors with organic electrolyte. The total pore volume and micro- and mesopore ratio were controlled by the activation temperature and alkali addition rate. The working characteristics of carbon electrodes (e.g., specific capacity and ohmic losses) in supercapacitors are strongly influenced by the properties of the pores in their structures. Herein, the optimal ratio of raw material to activator and activation temperature are established: an increase in the ratio of NaOH to carbonizate rate by a factor of 2 and setting the synthesis temperature at 700°C positively influence the electrochemical characteristics of supercapacitors and provide them with specific capacities of up to 160 F g-1.
Oligomeric proanthocyanidins (OPC) rich extracts (OPCEs) were isolated by sequential extraction from the bark of the deciduous trees grey alder (Alnus incana), black alder (Alnus glutinosa) and goat willow (Salix caprea). The yields of OPCE from all barks under study were rather similar and varied between 12.3% and 15.4% based on the oven dry (o.d.) bark. Content of proanthocyanidins in OPCEs ranged from 16.6% to 25% based on o.d. extract. The OPCEs were characterised by means of antioxidant activity with ABTS˙+ and DPPH˙ radical scavenging tests. All extracts being introduced into lipid-based substrates, i.e. mayonnaise and a basic composition of a cosmetic cream, showed antioxidant activity comparable to the reference commercial antioxidant tert-butylhydroquinone (TBHQ). The results of in vitro tests have revealed that the OPCEs could be useful for the human organism as they activated malfunctions of amylase, inhibited pancreatic lipase activity (duodenal digestion model), decreased lipid absorption in blood and decreased pyruvate level in blood plasma essential for regulation of carbohydrate metabolism. The data obtained confirms the advantages of OPC and OPCEs applications as an antioxidant additive for food, cosmetic and health industries.
The bark of trees has a big potential as a source of green chemicals. The aim of the present work was to valorise the potential of deciduous tree species with this regard. Three widely spread trees in Europe (grey alder, ash tree, aspen) were in focus as a source of polyphenols, and the yields of polyphenolic compound in the extracts were considered as evaluation criteria. The highest yields of hydrophilic extractives were found in barks of grey alder and aspen (36.8 and 22.9%, respectively). In the former, the highest antioxidant activity was found towards free radicals (DPPH• and ABTS•+) and superoxide anion radical. Open chain diarylheptanoids, mainly oregonin, were identified as the major constituents of the grey alder hydrophilic extract. In addition to oregonin, the presence of 2 linear diarylheptanoids [platyphylloside and 1,7-bis-(3,4-dihydroxyphenyl)-heptane-5-O-β-D-glucopyranoside] was confirmed. For the first time, the compounds 1,7-bis-(3,4-dihydroxyphenyl)-3-hydroxyheptane-5-O-β-D-xylopyranoside and 1,7-bis-(3,4-dihydroxyphenyl)-heptane-3-one-5-O-β-D-glucopyranoside were detected in grey alder bark. The results of experiments in vitro and in vivo have shown the high potential for diarylheptanoids-containing extracts in prophylaxis and/or treatment of diseases due to the metabolic disorders and ageing. The biological activity of grey alder extract was confirmed in in vitro experiments by incubation of human blood samples. In vivo experiments with rats also showed positive results. The conclusion is that grey alder extracts have a high potential for prevention of ageing related pathologies. Besides diarylheptanoids, the bark contains condensed tannins in commercially available quantity (12.5%). Eco-friendly wood adhesives were obtained on a tannins basis. The bark left after polyphenols isolation can be used in soil melioration and as a sorbent for the removal of oil products from water surface. The investigation of the phenolic pool of grey alder could contribute to cluster technologies within the biorefinery-based bark processing.
The new organosolv process of wheat straw fractionation elaborated by Compagnie Industrielle de la matiere Vegetale (France) corresponds to the biorefinery approach, which allows separating cellulose, hemicelluloses, and lignin. The straw lignin (Biolignin™) is an attractive product, for which new applications are sought. In the present work, straw lignin (L) was converted into liquid lignopolyols via a batch reaction with propylene oxide (PO). The effects of the lignin content (L%) in the initial reaction mixture (L/(L+PO) on the oxypropylation process and the properties of whole lignopolyols and L/PO copolymers were studied. Almost complete disappearance of L-OHphen and L-COOH groups in copolymers was accompanied by an increase in the L-OHaliph groups’ content therein. The polydispersity (Mw/Mn) of all copolymers obtained decreased essentially compared to the reference. The extent of PO grafting onto OH groups increased with decreasing lignin content in the initial reaction mixture. At a lignin content of 15–30% in the initial reaction mixture, the lignopolyols fulfil the requirements of polyol polyethers for rigid polyurethane foam production. The further increase in the lignin content leads to the appearance of the non-liquefied fraction and the undesirable increase in the viscosity of the liquefied part.