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Recovered papers contain several chromophores, such as wood lignin and dyes. These have to be eliminated during paper recycling in order to produce white paper. Hydrogen peroxide under alkaline conditions is generally used to decolorize lignin, but its effect on dyes is limited. Copper(II)-phenanthroline (Cu-Phen) complexes can activate the oxidation of lignin by hydrogen peroxide. Hydrogen peroxide may also be activated during recycled fiber bleaching, thus enhancing its color-stripping efficiency towards unoxidizable azo dyes. The purpose of this paper was to determine the effect of Cu-Phen complexes on a model azo dye, Direct Red 81 (DR81), in aqueous solution. Different Cu-Phen solutions (with different initial Cu:Phen molar ratios) were prepared and mixed with the dye at different pHs. The geochemical computer program PHREEQC allowed precise calculation of the theoretical distribution between different possible coordinates (CuPhenOH+, Cu(Phen)22+, CuPhen(OH)2, Cu(Phen)32+, etc.) depending on pH and initial concentrations. UV-vis spectroscopic measurements were correlated with the major species theoretically present in each condition. The UV absorbance of the system was mainly attributed to the Cu-Phen complex and the visible absorbance was only due to the dye. Cu-Phen appeared to reduce the color intensity of the DR81 dye aqueous solution under specific conditions (more effective at pH 10.7 with Cu:Phen = 1:1), probably owing to the occurrence of a coordination phenomenon between DR81 and Cu-Phen. Hence, the ligand competition between phenanthroline and hydroxide ions would be disturbed by a third competitor, which is the dye molecule. Further investigation proved that the DR81 dye is able to form a complex with copper-phenanthroline, leading to partial color-stripping. This new “color-stripping effect” may be a new opportunity in paper and textile industries for wastewater treatment. [ABSTRACT FROM AUTHOR]

The ClO2 titration method for in situ measurement of free phenolic groups in pulp has been improved to minimize interferences from other groups susceptible to react with ClO2. The method is based upon the reaction between free phenolic groups and chlorine dioxide at a temperature of 0°C, in the presence of dimethyl sulfoxide. Theoretically, one free phenolic group consumes two molecules of ClO2. The pH of the ClO2 treatment was advantageously fixed at 6.7 using a phosphate buffer, and a new protocol was proposed to avoid any possible interference of quinone groups (either present in pulp or formed during the procedure) on the residual ClO2 titration step. The results obtained on isolated lignin samples were compared to those measured by 31P NMR spectroscopy. The ClO2 method gave substantially higher values, for reasons which deserve further investigation. [ABSTRACT FROM AUTHOR]

Lignin is an aromatic biopolymer derived from lignocellulosic biomass. Providing a comprehensive structural analysis of lignin is the primary motivation for the quantification of various functional groups, with a view to valorizing lignin in a wide range of applications. This study investigated the lignin fluorobenzylation reaction and performed a subsequent 19F-NMR analysis to quantify hydroxyl groups, based on a work developed two decades ago by Barrelle et al. The objectives were to check the assignments proposed in this previous study and to examine the reactivity of various types of lignin hydroxyls with the derivatization agent. Selected lignin model compounds containing phenolic and aliphatic hydroxyls were subjected to the fluorobenzylation reaction, and the obtained reaction medium was analyzed by 13C and 19F NMR spectroscopy. The model compound results showed that phenolic hydroxyls were totally derivatized, whereas aliphatic hydroxyls underwent minimal conversion. They also confirmed that 19F NMR chemical shifts from −115 ppm to −117.3 ppm corresponded to phenolic groups. Then, a 19F NMR analysis was successfully applied to Organosolv commercial lignin after fluorobenzylation in order to quantify its phenolic group content; the values were found to be in the range of the reported values using other analytical techniques after lignin acetylation. [ABSTRACT FROM AUTHOR]

This work aims at elucidating some of the key steps of the oxidation pathways of lignin model compounds by hydrogen peroxide under alkaline conditions (0.05 M NaOH) in the presence of copper(II)-phenanthroline complex. Phenolic and non-phenolic β O 4 dimeric phenyl propane structures were selected as lignin models since they represent the most abundant structures in lignin: 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy) propane-1-ol and 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy) propane-1-one, and their methylated counterparts. After 3 h at 80 °C the main products in the reaction medium were analyzed by HPLC. The results suggested that the first step was the oxidation of the benzylic OH group to a ketone group. This step would be catalyzed by the copper (II)-phenanthroline complex and favored by the presence of dissolved oxygen. The second step would be the cleavage of the β O 4 linkage by a series of nucleophilic attacks initiated by the reaction of the perhydroxyl anion on the carbonyl group which would not be influenced by the presence of the copper complex. This mechanism is in accordance with the formation of acetaldehyde, veratric or vanillic acid, and guaiacol which were identified as the main reaction products of the models oxidation. [ABSTRACT FROM AUTHOR]