Study of complementary treatments in the bleaching process of eucalypt kraft pulps – handheets surface characterization using non conventional techniques (original) (raw)
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Bioresource Technology, 2010
The influence of different addition points of a chelating agent and a counter-ion exchange on the properties of Eucalyptus grandis unbleached kraft pulps is studied. Seven pulps were considered: two laboratory kraft pulps with or without the inclusion of the chelant DTPMPA (diethylene triamine penta (methylene phosphonic acid)), a mill kraft pulp and four mill pulps after Ca +2 or Na + counter-ion exchange followed, or not, by washing with DTPMPA addition. The laboratory pulps required lower beating energy than the industrial pulps for achieving 30°SR, and the corresponding handsheets also showed better strength and optical properties, as well as a more homogeneous and smooth surface. The counterion exchange decreases the mechanical resistances and increases brightness. However, the effects of Ca +2 are deeper than those of Na +. DTPMPA added to pulping causes a decrease in calcium content whereas as a washing additive does not have a relevant impact on the mechanical and optical properties.
This work evaluates the effect of SuperBatch™(SB), CompactCooking™(CC) and Lo-Solids™ (LS) modified cooking methods on the cell wall surface of Eucalyptus globulus and Eucalyptus nitens. The kappa target was 17±0.5. The pulps were bleached with sequence D0E1D1E2D2. E. globulus pulps presented higher screen yield and brightness than E. nitens which needed higher H-factor to reach kappa number target. Independently of the cooking method or species all the samples consumed similar amount of ClO2 to reach brightness of 90% ISO. E.nitens pulps showed lower carbohydrates and higher extractives content on fiber surface, regardless of the cooking method. E.nitens presented slightly higher surface charge of the bleached pulps. Surface charges of CC and LS pulps are higher independently of cooked Eucalyptus species. Water retention value (WRV) for E. nitens pulps were higher than for E. globulus. No differences were observed in refinability of different cooking methods, however E.nitens pulps showed higher tensile and lower bulk compared to E.globulus. No correlation between surface composition, fiber surface properties, and paper technical properties among the cooking methods could be determined.
We investigated the bleaching efficiency of the final chlorine dioxide (D2) stage in the D0(EP)D1D2 bleaching sequence, focusing on the effect of pH in relation to the bleaching history of pulp samples. The samples used were unbleached kraft Eucalyptus grandis pulps with kappa no. 14.8 and the same pulp oxygen-delignified to kappa nos. 12 and 9.8. The samples were bleached according to the D0(EP)D1 sequence to a brightness of about 86% ISO and then submitted to the final D2 stage under identical conditions (e.g., chlorine dioxide charge, time, tempera¬ture, and final pH). The target final brightness was 90.5% ISO. Changes in the kappa number, brightness, viscosity, and contents of hexenuronic acid), 4-O-methylglucuronic acid, and the total amount of carboxylic acid (COOH) groups in pulps were monitored during the bleaching sequence. The final brightness of eucalyptus kraft pulps increased when the terminal pH of the D2 stage was raised from 3.0 to 6.5. The 90.5% ISO target brightness in the D2 stage was achieved for all pulps within a pH range of 4.5–6.5, but this required adjusting final pH for individual sam¬ples. The optimal pH value with respect to pulp viscosity was between 3 and 5. Despite dissimilar conditions applied in previous bleaching stages, the samples after the D1 stage revealed similar residual lignin contents as shown by kappa number analysis. The content of hexenuronic acid in the samples, however, varied broadly, from 2 to 26 mmol/kg. Conductometric titration showed different amounts of carboxylic acid groups in pulps after the D1 stage, of which hexenuronic acid accounted for only a minor part. The variations in the fiber charge resulted from the different bleaching conditions applied before the D2 stage. The fiber charge affected the alkali demand in the final D2 stage, whereas variations in the alkali demand affected the initial pH and associated process kinetics. Lower total fiber charge was found to be beneficial for improved final brightening and viscosity when bleached at higher final pH.
Bioresources
The addition of a phosphonated chelant (DTPMPA) at different points of a TCF bleaching sequence and its effect on pulp properties were studied in this work. An industrial Eucalyptus grandis kraft pulp was submitted to a counter-ion exchange (Ca 2+ or Na + form) and was then bleached using DTPMPA in the washing or in the bleaching stages of two distinct sequences: OOpP and OQOpP (20 pulps). The counter-ion exchange affected fibre length, as well as the handsheets bulk and air permeability (higher for Na + -based pulps) and handsheet tensile strength, brightness, skeletal density, and total porosity based on Hg porosimetry (higher for Ca 2+ -based pulps). The hydrogen peroxide consumption in Op and P stages achieved the lowest values when the chelant was distributed rather than applied in a separate Q stage. The addition of chelant in the P stage provides pulps with higher ISO brightness (>85%). The chelant effects were always more noticeable in Ca 2+ -based pulps.
Bioresources, 2015
The SuperBatch™(SB), CompactCooking™(CC), and Lo-Solids™ (LS) modified cooking methods were evaluated relative to the cell wall surface and paper technical properties of bleached Eucalyptus globulus and Eucalyptus nitens. E. globulus pulps presented higher screened yield and brightness than E. nitens, which needed higher H-factor to reach a kappa number target. Independently of the cooking method or species, all the samples consumed similar amounts of ClO2 to reach a brightness of 90% ISO. E. nitens pulps showed lower carbohydrates and higher extractives content on the fiber surface, regardless of the cooking method. E. nitens presented slightly higher surface charge of the bleached pulps. Surface charges of CC and LS pulps were higher independently of cooked Eucalyptus species. Water retention value (WRV) for E. nitens pulps were higher than for E. globulus. No differences were observed in refinability of different cooking methods, however E. nitens pulps showed higher tensile and lower bulk compared to E. globulus. E nitens presented a thinner fiber cell wall than E. globulus. This seems to be more relevant for paper technical properties and WRV than fiber charge or surface composition. No correlation between surface composition, fiber surface properties, and paper technical properties among the cooking methods could be determined.
Tappi Journal
ABSTRACT: We investigated the bleaching efficiency of the final chlorine dioxide (D2) stage in the D0(EP)D1D2 bleaching sequence, focusing on the effect of pH in relation to the bleaching history of pulp samples. The samples used were unbleached kraft Eucalyptus grandis pulps with kappa no. 14.8 and the same pulp oxygen-delignified to kappa nos. 12 and 9.8. The samples were bleached according to the D0(EP)D1 sequence to a brightness of about 86% ISO and then submitted to the final D2 stage under identical conditions (e.g., chlorine dioxide charge, time, tempera-ture, and final pH). The target final brightness was 90.5% ISO. Changes in the kappa number, brightness, viscosity, and contents of hexenuronic acid, 4-O-methylglucuronic acid, and the total amount of carboxylic acid (COOH) groups in pulps were monitored during the bleaching sequence. The final brightness of eucalyptus kraft pulps increased when the terminal pH of the D2 stage was raised from 3.0 to 6.5. The 90.5% ISO target ...
Influence of Bleaching Sequences of Eucalyptus Kraft Pulp on the internal sizing of paper card
The packaging industry is a highlight, specifically the use of paper card which corresponds to 8% of the Brazilian production within the cardboard context, is the card for packaging liquid food that is ace for beverage packaging (such as milk and juice) and soft foods (as cream and tomato sauce). Due to economic globalization, there is the natural need of improvement of production processes. In this sense, there is the search for processes more economic, more effective and efficient, and environmentally friendly. It is most common to use rosin emulsions under mildly acidic conditions, e.g. between pH value of about 4.5 and 6. These conditions favor very high retention of alum or PAC (polyaluminum chloride) on the fibers. However, papers produced in higher pH shows better properties such as strength and viscosity. In this sense, there is a search for a type of rosin-based products to internal sizing in neutral/alkaline conditions. The aim of this study is to evaluate the influence of bleaching sequences of eucalyptus kraft- O2 pulp on the internal sizing of surface layer from paper card. Six different bleaching sequences, four ECF – D(E+P)DD; AHTD(E+P)DD; AHTD(E+P)DP; AHTDEDP one ECF-Light – AHTD(PO)D and one new ECF sequence – AHTDP are investigated. The pulps were bleached to 90 ± 0.5% ISO brightness. The pulps were refined in PFI mill and the refine curve was determined by previous tests. The pulps performed by 40° Schopper-Riegler (°SR). After that, the hand sheets (100 g/m²) were formed with 10 Kg/t of industrial rosin sizing agent plus 6 Kg/t of industrial PAC at pH 7,0. The quality parameters analyzed were Cobb test, Edge wicking peroxide and Edge wicking lactic acid.
Progress in eucalyptus kraft pulp bleaching
… sobre celulosa kraft …, 2005
Bleached eucalyptus kraft pulps are largely used for manufacturing tissue and print & writing (P&W) paper grades. High final brightness (92 + % ISO) and brightness stability (<2% ISO) are rather significant for P&W for it affects optical brighteners demand. Bleaching chemical demand, bleaching yield, water consumption, effluent load & treatability, pulp OX, brightness stability, refinability and strength are drivers for choosing bleaching technology. This work critically reviews the state-of-the-art processes for oxygen delignification, first stage, second stage and final bleaching of eucalyptus kraft pulp in the light of the aforementioned drivers. The potential of new bleaching technologies such as the P Mo stage and the use of formaldehyde in D-stages are also presented. Implementation of single or double-stage oxygen delignification is determined by the true pulp lignin content (discounted the HexA´s). The high pulp HexA´s content and poor oxygen stage selectivity limits dropping kappa number under 9-10 in single or double Ostage. Application of Mo-catalyzed acid peroxide delignification after O-stage allows further reduction of kappa number to 3-4. Efficient post-oxygen washing is the key for low cost bleaching, with a kg of COD/odt consuming the equivalent to 0.085% active chlorine. A D-(EP)-D type three stage sequences suffices for bleaching eucalyptus kraft pulps. The inclusion of a fourth stage is desirable for production of high brightness/ low reversion pulps. Bleaching chemical consumption is strongly influenced by brown pulp origin, with variations of 3.2 to 7.7% active Cl 2 demand depending upon the pulp type. The type of ECF Bleaching technology, based on chlorine dioxide, affects chemical consumption only slightly. Hot acid/hot chlorine dioxide bleaching technology saves small amounts of active chlorine for high bleachability pulps but none for low bleachability ones. Atmospheric extraction (EP) suffices for eucalyptus kraft pulp bleaching. Formaldehyde saves more chlorine dioxide when used in D 1 than in D 0 /D HT stages. A final peroxide stage significantly improves pulp brightness stability. The production or organically bound chlorine decreases by 30% with hot chlorine dioxide bleaching but this gain disappears after effluent biological treatment.