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 P-stage 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 The aim of the present study is to investigate the dissolving ability of a cellulosic substrate using a derivatization method, i.e. cellulose tricarbanilation and the follow-up by dynamic light scattering (DLS), for particle size measurement. The dissolving behavior of six commercial pulps, selected for their different nature and properties, were compared to the Fock test, and the analysis was completed by other methods for substrate characterization: crystallinity (XRD), DPv (in CuED), sugar analysis, molecular weight distribution (MWD) of cellulose by HPSEC-multidetectors (done on the cellulose tricarbanilates), and solubility in NaOH:urea:water. The proposed carbanilation/DLS method resulted practical and suitable for evaluating the dissolving ability of the different pulps – including hemicelluloses-containing kraft pulps – and allowed to discriminate the samples, contrary to the Fock test. Comparison and assessment of the relevance of the different methods are finally discussed.

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.

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) 2(2+), CuPhen(OH)(2), Cu(Phen)(3)(2+), 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.

Our project aims at developing a biorefinery integrated in the recycling line of paperboard, where would be separated from recovered fibers prior to the production of paperboard. The extracted could then be valorized, which requires its characterization. Corrugated board made from fibers was re-dispersed in water and filtered. Almost 100% of the initially present in the corrugated board was found in the filtrate. Asymmetric Flow Field-Flow Fractionation (A4F) coupled with multi-angle light scattering and differential refractive index detection was used to measure the molecular weight distribution of the extracted starch. This was welded by ultrasonic compression and the rigidity of the resulting structure was compared to commercial starches. Overall, this recycled starch showed promising results.

AbstractRecovered 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 H2O2on 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 H2O2bleaching. 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 H2O2color stripping, although it was accompanied by additional cellulose degradation. Moreover, the color stripping was more effective under alkaline conditions, in which case CuPhen(OH)2would be present. Two hypotheses are proposed to explain this activated decolorization: a free radical mechanism and the influence of CuPhen(OH)2as an activating species.

Etude de l'activation du peroxyde d'hydrogène par le complexe cuivre(II)-phénanthroline pour la décoloration de fibres cellulosiques récupérées Les papiers récupérés sont de plus en plus utilisés pour fabriquer du papier recyclé de haute blancheur. La ligne de recyclage inclut entre autres les opérations de désencrage et de blanchiment, le peroxyde d’hydrogène (H2O2) étant le réactif blanchissant le plus utilisé en milieu alcalin (stade P). Son efficacité est toutefois limitée car il est peu ou moyennement réactif sur les fonctions azoïques des colorants papetiers. L’objectif de cette étude était donc d’améliorer l’élimination des colorants azoïques lors d’un stade P.L'amélioration du stade P utilisé en délignification des pâtes chimiques a fait l’objet de nombreuses études. En particulier, l’activation ou la catalyse de H2O2 par des complexes cuivre(II)-phénanthroline (Cu-Phen) présentant des résultats très intéressants, des essais de blanchiment de pâtes désencrées et colorées ont été entrepris. Le système H2O2/Cu-Phen s’est également révélé efficace en décoloration, mais le mécanisme n’avait alors pas été étudié.L’objectif de ce travail était donc de déterminer dans quel cas et pourquoi le complexe cuivre(II)-phénanthroline était capable d’améliorer la décoloration de fibres cellulosiques colorées. Trois questions intermédiaires se sont posées : (1) quel effet Cu-Phen a-t-il sur le colorant isolé? (2) la décoloration d’une pâte de fibres colorées par H2O2 est-elle améliorée par Cu-Phen? (3) par quel mécanisme la décoloration est-elle rendue plus efficace?Le travail a donc été organisé en trois études : (1) caractérisation des colorants sélectionnés et du complexe en l’absence d’oxydant et examen des interactions entre les deux, (2) étude et optimisation paramétrique de H2O2/Cu-Phen pour la décoloration de pâtes colorées, (3) étude du mécanisme d’oxydation en milieu aqueux, en l’absence et en présence de cellulose.Ce travail s’est appuyé sur de nombreuses techniques analytiques (spectroscopies RMN, FTIR, UV-vis et RPE ; ESI-MS) et des calculs de spéciation. Il a prouvé que le complexe Cu-Phen en présence de H2O2 améliorait la décoloration de colorants azoïques, avec ou sans fibres cellulosiques. Il a été mis en évidence que la phénanthroline agissait comme un stabilisant permettant d’ajuster la solubilité, la stabilité et le potentiel d’oxydo-réduction du cuivre(II), mais qu’elle n’était pas indispensable. De plus, le pH du milieu est également un paramètre clé, jouant à la fois sur l’activité du complexe et sur ses interactions avec le substrat. Le substrat (colorant mais aussi cellulose) s’est trouvé fortement dégradé par ce système H2O2/Cu-Phen. Les résultats corroborent l’hypothèse de l’oxydation du substrat par les radicaux hydroxyles issus de la décomposition de H2O2, plutôt que par H2O2 lui-même, ce mécanisme étant l’une des étapes d’un cycle catalytique.La recherche menée et les résultats obtenus sont applicables non seulement à l’amélioration du blanchiment des pâtes désencrées, mais aussi au traitement d’effluents colorés dans les industries du papier et du textile.