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Paper recycling systems based on flotation technologies are not efficient to deink secondary fibers from new printing technologies based on flexographic inks which, even being more environmentally friendly, still present some recycling problems. We have evaluated the efficiency of a biotechnological approach, based on the laccase-mediator system, for biodeinking of three flexographic inks (Blue 1, Magenta HX-E and Red 48:4) in the presence of several pulps (bleached pulp, deinked paper pulp from secondary fibers and pulp from commercial uncoated and coated office paper sheets). Two fungal laccases, one from the basidiomycete Coriolopsis rigida and the other from the ascomycete Myceliophthora thermophila , were used as catalysts in the presence of HBT (1-hydroxybenzotriazole) or methyl syringate, as models of synthetic and natural mediators, respectively. Higher decoloration rates were achieved for Blue 1 and Magenta HX-E than for Red 48:4. The best results were obtained using bleached pulps without additives. Then, to identify the chemical compounds that may hamper enzymatic biodeinking, the influence of several additives on ink decoloration and enzyme activity was tested. Only calcium carbonate slowed down ink decolorization by up to 40%, although it also decreased the mediator assisted enzyme deactivation. In this work, a system to evaluate the efficiency of the laccase-mediator system in biodeinking of flexographic inks in the presence of different pulps and papers has been developed.

Fiber crops constitute a good alternative to wood fiber for manufacturing pulp and paper. In fact, fiber plants like flax surpass wood fiber in some technical respects and also in the environmental benignity of their processing. In this work, flax fiber was subjected to environmentally friendly bleaching sequences in order to obtain a high-quality pulp. The totally chlorine-free sequences (TCF) used for this purpose (LE and LRE) included an enzyme treatment with laccase in the presence of HBT as mediator (L stage), an alkaline extraction (E stage) and a reductive treatment with NaBH 4 (R stage). The operating conditions for the L stage (laccase and HBT doses, reaction time and oxygen pressure) were optimised by using a sequential statistical plan to assess their influence on pulp properties after the E stage. Mathematical models accurately predicting brightness and kappa number in terms of the previous four variables were developed based on which the most influential factors were the laccase and HBT rates, and treatment time. By contrast, oxygen pressures of 0.2–0.6 MPa in the reactor had no effect on brightness or kappa number. The flax pulp obtained contained some oxidized cellulose that was partially degraded in the alkaline extraction step and reduced viscosity as a result. The viscosity loss associated with the presence of oxidized cellulose in the control and enzyme-treated pulp samples was efficiently recovered by using a reductive stage with sodium borohydride. Effluent was also analysed in order to assess the environmental impact of the process.

7 páginas, 6 figuras, 4 tablas -- PAGS nros. 181-187, High-quality flax pulp was bleached in a short totally-chlorine-free (TCF) sequence. The LP biobleaching sequence includes an enzyme treatment with laccase in the presence of HBT as mediator (L stage) and a hydrogen peroxide stage (P stage). The operating conditions for the laccase HBT system were optimized by using a sequential statistical plan involving four variables, the influence of which on the properties of the pulp after the P stage was examined over enclosed operation conditions regarding a future industrial application. Mathematical models accurately predicting both pulp properties in terms of the previous four variables. This biobleaching sequence allows obtaining an increase in ISO brightness of 40% and a delignification of 80%. Process variables optimization in flax pulp biobleaching allows establishing the application conditions most appropriated to obtain certain pulp properties and that turn out to be easily adaptable to existing industrial processes. As a novelty, toxicity measurements were determined in L stage effluents. The results of toxicity show that it is possible to apply this LP sequence without having a negative environmental impact

Flax pulp was bleached by using an enzyme treatment with laccase (L stage) in the presence of HBT as mediator in order to replace toxic chemicals (e.g. chlorine or chlorine dioxide) with environmentally friendly catalytic biotechnological products in the bleaching process, achieving a clean process technology in the pulp and paper manufacture. The operating conditions for the laccase–HBT system were optimized by using a sequential statistical plan involving four variables (laccase dose, HBT dose, treatment time and oxygen pressure), their influence on the properties of the pulp after the L stage was examined. The main objective was to minimize the reagent doses and the reaction time to make more suitable the industrial application. A mathematical model for predicting the kappa number in terms of the process variables was developed. The kappa number decreased with increase in the value of each variable down to a minimum level of 6.9, which was obtained with a laccase dose of 13 U g−1, an HBT dose of 2%odp and a treatment time of 6.5 h. The model predicted a limiting laccase dose of 13 U g−1 above which no additional reduction in kappa number would be obtained. By contrast, oxygen pressures of 0.2–0.6 MPa in the reactor had no effect on brightness or kappa number. Brightness was not correlated with the kappa number due to the formation of chromophores in the pulp at the beginning of the enzymatic treatment. The LP biochemical sequence allows obtaining a final brightness of 75.2%ISO.

The influence of a treatment with two commercial xylanases on pulp and effluents obtained after the bleaching stages in the OXAZDP (O, oxygen stage; X, xylanase treatment; A, acid stage; Z, ozone stage; D, chlorine dioxide stage; P, hydrogen peroxide stage) sequence was studied. Also, the potential saving in chlorine dioxide was assessed. The enzyme treatment was performed on pulp containing some black liquor since the operating conditions were close to the conditions used in the storage tower in Fibria, identified as the most suitable point for application. The greatest differences in kappa number and hexenuronic acid content were observed after the X stage. Whereas, in brightness were observed after the Z stage. The effluent properties from the X stage were higher with the enzyme treatments. Also, the enzymes allowed chlorine dioxide consumption in the bleaching stage to be reduced. The control pulp contained twice as much adsorbable organic halides (AOX) and exhibited twice more brightness reversion than did the enzyme-treated samples. However, the tensile index and drainability at an identical degree of refining were lower in the enzyme-treated samples

7 páginas, 5 figuras, 2 tablas -- PAGS nros. 97-103, The use of new printing technologies based on flexographic inks hampers ink elimination during paper recycling, making necessary the development of alternative methods. Decolorization of four flexographic inks has been evaluated by using fungal laccases, three of them from basidiomycetes (Trametes villosa, Coriolopsis rigida, and Pycnoporus coccineus), and one from the ascomycete Myceliophthora thermophila in the presence of synthetic and natural mediators. The results obtained showed a higher capacity of the three basidiomycete laccases to decolorize flexographic inks as compared with M. thermophila laccase, a low redox potential laccase. Basidiomycete laccases decolorized inks without mediators at long reaction times, although the presence of natural or synthetic mediators (above all HBT) accelerated the process. On the other hand, M. thermophila laccase was unable to decolorize the inks assayed. The addition of syringyl-type mediators led to medium levels of decolorization except for R48 ink, which was almost completely decolorized. Most decolorization was obtained during the first hours of treatment, when all the basidiomycete laccases were fully active in the presence of mediators. As opposed to other basidiomycete laccases, which become inactive in the presence of HBT after 24 h, the enzyme of P. coccineus was not deactivated by this mediator even after 48 h. A complete loss of M. thermophila laccase activity was observed at short times with acetosyringone and methyl syringate, the only two mediators able to promote ink decolorization with this enzyme, This work has been funded by PROLIPAPEL II S-2009AMB-1480 project (Comunidad de Madrid) and PRI-PIBAR-2011-1402. The authors are grateful to Novozymes® for kindly supplying laccases and to Quimovil SA and Flint Group Iberia SA for providing flexographic inks

6 páginas, 10 figuras -- PAGS bros. 193-198, In this study we examined the influence of the treatment time and addition of oxygen on the efficiency of a laccase mediator system (L) applied to flax pulp at atmospheric pressure. The redox potential and the dissolved oxygen concentration during L tests are measured. After L stage, an alkaline extraction (E) is carried out. The pulp properties (kappa number, brightness and viscosity) and the effluents properties (color and COD) were measured in order to evaluate the environmental impact of this enzymatic treatment. The biotreatment involves two distinct stages in both L and LE sequences; in the beginning the pulp exhibits a fast delignification and a slow viscosity decrease that is followed by slow delignification in the second. Pulp brightness changed differently during L stage and LE sequence. Initially brightness after the L stage decreased with respect to the initial pulp; then, it increased rapidly and eventually leveled off. After the LE sequence, brightness increased rapidly in the beginning and more gradually afterwards. The results show that supplying the medium with oxygen and increasing the oxygen concentration in it, influence the kinetics of the process. Based on CIE L*a*b* color coordinates study, the enzyme treatment not only removes lignin, but also alters the structure of the pulp by causing the formation of chromophoric groups giving color. Such groups are removed in an E stage., Spanish MEC ENZPULP Project (CTQ2005-08925-C02-01) and a BIORENEW Integrated European Project (NMP2-CT-2006-026456). Department of University, Research and Society of the Information of the Generalitat de Catalunya and the Social European Fund for the research fellowship (2005 FI grant)

9 páginas, 8 figuras, 7 tablas -- PAGS nros. 330-338, Flax pulp was bleached by using an enzyme treatment with laccase (L stage) in the presence of HBT as mediator in order to replace chlorine-based pulp bleaching processes which produce toxic organochlorine compounds with biotechnological products, achieving an environmentally friendly process technology. Enzyme treatments were sequentially conducted according to a factorial design involving four variables: laccase dose, HBT dose, treatment time and oxygen pressure in the reactor. Their influence on the effluent properties (COD, color, toxicity, spectra and residual enzymatic activity) was examined to evaluate the impact of L stage on environment since no experimental data have been published concerning this matter. Mathematical models accurately predicting effluent properties in terms of the previous four variables were developed. High COD levels were obtained as a result of using commercial laccase. Also, red color produced, especially at long treatment time, relates to formation of oxidation products from HBT. The residual enzymatic activity depends basically on mediator dose, and mainly activity loss is produced during the first 30 min of treatment. The toxicity of the effluents was below the limits set by the sewage regulations for Catalonia and can be ascribed to the combined effect of the laccase-mediator system., MEC ENZPULP Project (CTQ2005-08925-C02-01) and a BIORENEW Integrated European Project (NMP2-CT-2006-026456). Department of University, Research and Society of the Information of the Generalitat de Catalunya and Social European Fund for the research fellowship (2005 FI grant).

To obtain a more realistic appraisal of the potential efficiency of xylanases in the industrial bleaching, the influence of pH and the presence of black liquor (measured as COD) on the bleaching efficiency of two commercial xylanases was studied at high temperature. These pH’s, CODs, and temperatures are close to those used in the storage tower of the B fiber line in Jacareı´ unit of Fibria (Brazil). The pulp samples obtained after each bleaching stage were analyzed for kappa number, brightness, viscosity, and hexenuronic acid content, and so were the effluents for COD, TOC, color, turbidity, and pH after the enzymatic stage. On the basis of the results, the xylanases were found to increase pulp brightness in the treatment involving the most unfavorable conditions (viz. high COD and pH). However, an initial COD above 9 kgO2 t-1 and/or a pH higher than 9.5 detracted from their bleaching efficiency. The effect on the kappa number and hexenuronic acids content of the pulp was apparent immediately after the enzymatic stage, and the most marked increase in brightness was observed after the chlorine dioxide stage.