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Converting paper-grade bleached Kraft pulp into dissolving pulp using eco-friendly chemicals on-site at the mill is a challenge for the pulp industry. In this study, two oxidation systems are evaluated: the first one is based on the use of hydrogen peroxide at various levels of alkalinity; the second one investigates the use of sodium periodate followed by hydrogen peroxide to convert aldehydes into carboxyls and enhance their hemicelluloses removal. Our results have shown that when using only peroxide, the removal of hemicelluloses was not sufficient to improve the pulp's dissolving ability. Conversely, the periodate–peroxide system proved to be more efficient. Results regarding the pulp purity, solubility, degradation (pulp viscosity and cellulose molecular mass distribution), brightness, and its potential applications were discussed. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide is an environmentally friendly bleaching chemical that is widely used in alkaline media in the pulp and paper industry. In this study, unconventional reaction conditions of the conventional bleaching Pstage were performed to evaluate its effect on cellulose. The objective was to “tailor” the cellulose degradation according to different applications, such as dissolving pulps. Different operating conditions were studied: pH variation (alkaline or acidic medium), as well as the addition of Cu(II) or the Cu(II)-phenanthroline complex. The hypotheses considered were (1) Using H2O2 in unconventional conditions will favor hemicelluloses removal after depolymerization and will lead to the desired cellulose degradation, and (2) H2O2 oxidation carried out under unconventional conditions will favor the dissolving ability of cellulose. [ABSTRACT FROM AUTHOR]

The copper–phenanthroline complex CuI(Phen)2 was the first artificial nuclease studied in biology. The mechanism responsible for this activity involves CuII(Phen)2 and H2O2. Even if H2O2/Cu systems have been extensively studied in biology and oxidative chemistry, most of these studies were carried out at physiological pH only, and little information is available on the generation of radicals by the H2O2/CuII-Phen system. In the context of paper pulp bleaching to improve the bleaching ability of H2O2, this system has been investigated, mostly at alkaline pH, and more recently at near-neutral pH in the case of dyed cellulosic fibers. Hence, this paper aims at studying the production of radicals with the H2O2/CuII-Phen system at near-neutral and alkaline pHs. Using the EPR/spin-trapping method, HO• formation was monitored to understand the mechanisms involved. DMPO was used as a spin-trap to form DMPO–OH in the presence of HO•, and two HO• scavengers were compared to identify the origin of the observed DMPO–OH adduct, as nucleophilic addition of water onto DMPO leads to the same adduct. H2O2 decomposition was enhanced by the addition of CuII–Phen (and only slightly by addition of CuSO4), reaching a level similar to the Fenton reagent at near-neutral pH. This evidences the role of Phen, which improves the effect of CuII by tuning the electronic structure and structural properties of the corresponding CuII complexes. [ABSTRACT FROM AUTHOR]

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]

Recovered fibers are reused for manufacturing bright paper after deinking and fiber decolorization. This second process generally starts with an alkaline hydrogen peroxide (H2O2) stage, referred to as P. However, the color-stripping effect of P is often limited due to the low reactivity of H2O2 on the azo groups of dyes. The purpose of this study was to improve the removal of these azo dyes by H2O2. A bleached kraft pulp was dyed with a model azo dye and submitted to activated H2O2 bleaching. Phenanthroline and copper(II)-phenanthroline (Cu-Phen) served as activating compounds. The color-stripping trials were carried out at weak or conventional alkaline pH. The results were mainly evaluated in terms of dye removal index and degree of polymerization of cellulose. The theoretical composition of Cu-Phen in the bleaching conditions was calculated by means of the geochemical software PHREEQC. The results show that Cu-Phen was able to activate H2O2 color stripping, although it was accompanied by additional cellulose degradation. Moreover, the color stripping was more effective under alkaline conditions, in which case CuPhen(OH)2 would be present. Two hypotheses are proposed to explain this activated decolorization: a free radical mechanism and the influence of CuPhen(OH)2 as an activating species. [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]

Microfibrillated cellulose (MFC) is an emerging cellulosic material that has shown enormous potential in various industrial sectors such as food packaging, cosmetics, pharmaceuticals, filler for cement and paper, and others. Yet, there is still the need to improve its processing in order to reach its full potential. Despite research efforts for the production of MFC, the production volumes remain low because the costs of these products are hardly competitive with synthetic polymers. The present study investigates the conversion of bleached Kraft pulp into MFC using three different oxidative treatments: (1) oxidation with sodium periodate followed by oxidation with hydrogen peroxide to enrich the pulp with carboxyl groups; (2) activation of hydrogen peroxide with copper to produce hydroxyl radicals; and (3) use of hydrogen peroxide alone in alkaline medium. Treatments (1) and (2) allowed producing interesting MFC with reduced energy consumption. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] Pure cellulose was produced from a hardwood Kraft pulp. [•] A totally chlorine-free process was applied on the unbleached pulp. [•] Hydrogen peroxide delignification catalyzed by copper phenanthroline was applied. [•] Cold caustic extraction and ozonation were used to complete the process. [•] The bleached cellulose exhibits the quality of a dissolving pulp. [ABSTRACT FROM AUTHOR]