Pulp Brightness Research Articles

Extension of a steady-state chlorine dioxide brightening model for Z-ECF bleaching of softwood kraft pulps

Earlier studies developed a steady-state model to predict the brightness and/or bleach consumption during the chlorine dioxide brightening (D1) of softwood pulps produced by conventional elemental-chlorine-free (ECF) sequences. This model relates the chlorine dioxide consumed to the brightness gains predicated upon an asymptotic D1 brightness limit, an incoming D1 pulp brightness, and an equation parameter (β11). The current investigation examines the application of this model to ECF sequences that use ozone delignification (Z-ECF). Literature D1 data from various Z-ECF bleaching studies, which investigated OZ, OD0/Z, and OZ/D0 delignification, were fitted to the model. The β11 parameter was found to be linearly correlated to the entering kappa number. Interestingly, this linear relationship was found to be identical to the relationships observed when modeling the D1 stage for conventional ECF and chlorine-based bleach sequences. Subtle differences in D1 brightening response in the model among the various bleach sequences are reflected by incoming pulp brightness (at the same kappa number). The current model is used to illustrate how alterations to Z-ECF delignification affect D1 brightening and chlorine dioxide consumption.

BIOBLEACHING OF ETHANOL-SODA PULP OF EULALIOPSIS BINATA BY XYLANASES FROM ASPERGILLUS FLAVUS ARC-12 AND SCHIZOPHYLLUM COMMUNE ARC-11

Environmental pollution can be minimized by using xylanase pretreatment of pulp before chemical bleaching. A. flavus ARC-12 and S. commune ARC-11 produced 234.26 and 1147.11 IU/ml of xylanase under solid-state fermentation that was used for biobleaching of ethanol-soda pulp of Eulaliopsis binata. The brightness of bleached ethanol-soda pulp of E. binata increased by 3.2 and 1.9% (ISO) with A. flavus ARC-12 and S. commune ARC-11 xylanase respectively compared chemical bleaching at the same chlorine dioxide charge. While the consumption of chlorine dioxide were mitigated by 2.98 and 3.82% with A. flavus ARC-12 and S. commune ARC-11 xylanase pretreatment respectively. Moreover, A. flavus ARC-12 and S. commune ARC-11 xylanase pretreatment reduced AOX generation by 23.80 and 19.04% respectively compared to chemical bleaching.

Hemicellulose and hexenuronic acid removal selectivity to give boosting effect to ECF bleaching

Varies wood structure need difference way of treatment to get the appropriate quality of wood pulp. In pulp industry, wood chips should be cooked and bleached in order to have a good quality of pulp suitable for paper industry. A modified pulp cooking such as Continuous Isothermal Cooking and Super Batch Cooking followed by ECF bleaching is a good alternative for the achievement the necessary standard quality. Effort to achieve better quality in higher yield has so many times been done. Enzyme treatment using xylanase using Ecopuylp TX-200 is a good alternative that could be done in the ECF bleaching stage. Two kinds of unbleached wood pulp from Eucalyptus camaldulensis from AA Thailand, Acacia mangium from RAPP Indonesia is used in this experiment. The bleaching results are analysed for yield, viscosity, hexenuronic acid content, and brightness. The results give an indication that wood structure has a close correlation with the accessibility of enzyme and chemistries in giving peeling effect of lignin from lignin carbohydrate complex (LCC) to get high brightness of pulp with minimum fibre losses. The presence of Na2CO3 in the cooking liquor to gather with the xylanase has positive effect in the cleavage of hemicellulose and lignin through hydrogen bond at – OCH3.

Effect of deinking and peroxide bleaching on the physical properties of recycled newspapers

Paper recycling for producing a new paper that can be used from old spent paper has gained increased interest, and this process helps prevent the paper from accumulating in landfills, reducing pollution and greenhouse gas emissions. In this work old newspaper (ONP) supplied from Al-Ahram Press is de-inked by washing process using sodium hydroxide, surfactant then hydrogen peroxide was applied to bleach the recycled deinked ONP. Following single-stage bleaching, the fiber properties of the pulp (brightness, tensile, tear strength, and burst index) were determined. The Effect of hydrogen peroxide dose, consistency, and temperature on the pulp brightness were studied. The deinking step produces deinked pulp with low brightness 51.75% ISO and the single-stage peroxide bleaching applied to the deinked ONP pulp could produce pulp with brightness 64.05% ISO at 60 min, 80°C, H2O2 concentration 2% and consistency 20%. The obtained data showed that the brightness of the deinked ONP increases with increasing hydrogen peroxide dose, consistency, and temperature. Also, it was found that the tensile strength and burst index increase by increasing brightness while, tear strength decreased.

Recirculation of treated effluent in the bleaching of kraft pulp

The bleaching plant of a kraft pulp mill is the sector that consumes water and generates effluent with the highest volume. Water recycling is an attractive option to reduce water consumption and effluent generation. This study evaluated the technical feasibility of using treated effluent as washing water in the bleaching stages. The bleaching sequence was simulated in the laboratory using four types of washing water: deionized water, whitewater, low organic load effluent, and high organic load effluent. To achieve 90% ISO pulp brightness, the ClO2 consumption increased from 8.1 kg ClO2 odt-1 when using water to 13.8 and 16.3 kgClO2 odt-1 for the low and high organic effluents. Physical and optical tests of the hand-sheet papers did not show any statistical difference between various washing waters. The filtrates showed values that did not burden the efficiency of the effluent treatment plant. It was possible to use effluent in the bleaching stages, considering that the filtrates and the produced paper complied with the quality standards.

Yield loss during bleaching of pulp of Pinus radiata previously delignified with oxygen.

The pulp bleaching process removes or transforms the chromophore groups in the pulp, so that the final product reaches a desired brightness. However, this chemical treatment inevitably results in yield loss. Therefore, the objective of this work was to quantify the yield loss caused during the bleaching of kraft pulp of Pinus radiata delignified with oxygen. The material was submitted to three distinct ECF sequences (D0(EPO)D1D2, D0(EPO)D1P, and Z/EDP). At the end of each bleaching stage, the pulp brightness and the loss of gravimetric yield of the process were determined, and the generated filtrates were collected. From these filtrates, the pollutant load of the effluent was determined by measuring the content of total dissolved solids, the chemical oxygen demand, the concentration of total organic carbon carbon, and the adsorbable organic halogens. Among the whole sequences, the Z/EDP sequence had the lowest gravimetric yield, the highest pollutant load in the collected filtrate, and lowest potential for adsorbable organic halogens generation. There was good correlation between the loss of yield from the bleaching process and the organic load of the generated effluent; and among the techniques studied, the quantification of total organic carbon was the most appropriate method for the indirect quantification of the yield loss during the bleaching process of the studied material.

Chlorine dioxide bleaching of nineteen non-wood plant pulps

AbstractBleaching of unbleached and oxygen delignified pulps from nineteen non-wood plants has been evaluated in elemental chlorine free bleaching. Chlorine dioxide charge (kappa factor 0.15, 0.20 and 0.25) and temperature (70 and 85 °C) in the delignification stage (D) were varied. Chlorine dioxide (ClO2) charge and temperature exhibited lower kappa number and higher brightness after alkaline extraction (EP) stage. High temperature ClO2delignification (DHT) exhibited higher final pulp brightness. The final brightness of wheat straw pulp reached to 90 % after D0/DHT(EP)D1bleaching, while banana pseudo stem pulp showed the worst bleachability. Residual hexeneuronic acid contents in final pulp from most of the non-wood plants were lower and exhibited 1–2 % higher pulp brightness in DHTprocess than D0process. Oxygen delignified pulp and DHTprocess discharged lower COD load.

Partial circuit closure of filtrate in an ECF bleaching plant

Abstract The bleaching sector of the wood pulp industry is its largest effluent generator. The aim of this study was to reuse the bleaching filtrate in order to reduce water consumption. The experiment was conducted by simulating the D0(EP)D1 bleaching sequence and recirculating different amounts of filtrate from the oxidation stage to control the pulp consistency of the delignification stage (pre-O). Physical, mechanical, chemical and optical properties of the pulp were studied. The accumulation of the non-process elements (NPE) and their effects were evaluated with the Aspen-Plus® computer simulator. The results of the computational modeling were satisfactory. The recirculation of filtrates increased the saturation index of the system by 19 %, but remained at sub-saturation levels. The pulp viscosity and elongation remained statistically stable. Recirculation of up to 50 % of the filtrate did not produce differences in pulp brightness; however, there were slight losses in the pulp resistances. In order to maintain 84 % ISO brightness, there was a higher consumption of the bleaching reagents. Up to 50 % of recirculation of the filtrates was accomplished without jeopardizing the system and the pulp quality and resulted in a savings of 55 m3 h−1 of water – 7 % of the consumption of the entire mill.

Eco-friendly pulping of wheat straw using crude xylano-pectinolytic concoction for manufacturing good quality paper.

In this study, suitability of xylano-pectinolytic enzymes in pulping of wheat straw has been explored. The suitable biopulping conditions were optimized, with xylanase dose of 400 and pectinase dose of 120IU/g wheat straw, 1:10 (g/ml) material to liquid ratio, 55°C temperature, 3h treatment time, 0.75% Tween 80 and pH8.5. Enzymatic pretreatment efficiently increased the pulpability of wheat straw, generated pulp with higher yield, lower kappa number (15.67%) and rejections (59.65%) in comparison with chemical pulp. The brightness of pretreated wheat straw pulp with enzyme was 16.04% higher than that of the non-enzyme treated wheat straw pulp. The biopulping resulted in 12% reduction of pulping chemicals along with more residual alkali content, in order to achieve similar optical and chemical properties as obtained by 100% chemically treated pulp. Physical properties of pulp also improved after enzymatic pretreatment, increasing burst index (26.50%), tear index (18.22%) and breaking length (5.56%). The enzyme plus chemical (88% pulping chemicals) treated pulp showed improvement in brightness and whiteness, with reduction in yellowness at all bleaching stages. In comparison with chemically bleached pulp, biopulp with reduced alkali dose (88%) had higher breaking length (6.63%), double fold number (51.28%), tear index (2.83%), burst index (24.31%), along with increased viscosity (6.12%) and Gurley porosity (27.50%). These results clearly suggest that biopulping of wheat straw with xylano-pectinolytic enzymes can reduce chemical loading during soda-anthraquinone pulping and also improve the quality of paper. This is the first report demonstrating the biopulping of wheat straw using crude xylano-pectinolytic enzymes.

Development of a fast brightness testing method for mechanical pulp based on microwave oven drying

Brightness is an important quality parameter for pulp products, and it is important to have reliable measurement of pulp brightness in a timely manner for process control and/or quality control purposes. In these circumstances, a quick testing method for pulp brightness is highly desirable. A rapid handsheet brightness testing method for lignin-rich mechanical pulp has been developed, which is based on the use of tap water to make handsheets and microwave ovens to rapidly dry the handsheet. Microwave oven fast drying decreased the handsheet brightness of mechanical pulp by 5–6 points due to the lignin-originated discoloration reactions. The spray of ascorbic acid and ethylenediaminetetraacetic acid (EDTA) solutions to the handsheet can effectively inhibit these lignin discoloration reactions. With 0.2% ascorbic acid and 0.2% EDTA spraying on the wet pulp handsheet, the brightness of the handsheet from a peroxide-bleached stone groundwood pulp after the microwave oven fast drying method was similar to that obtained from the same pulp but following TAPPI Standard Test Method T 272 sp-12 “Forming handsheets for reflectance testing of pulp (sheet machine procedure)”. The effect of handsheet dryness on the handsheet brightness was also studied, and the results showed that the brightness reading was almost constant in the dry-ness range of 70% to 90%. The method developed is a reliable, fast brightness testing method for lignin-rich pulp that is of practical interest in industrial operations.

Effects of Hot Water Pre-Extraction on Energy Consumption and Brightness of Bamboo Alkaline Peroxide Mechanical Pulp

The main purpose of this paper was to investigate the effects of hot water pre-extraction (HWP) on the refining energy consumption and the brightness of bamboo alkaline peroxide mechanical pulp (APMP). It was found that compared with un-extraction, the refining energy consumption dropped by about one-third after HWP. The reduction of energy consumption was proved through enhancing the channel of water and chemicals into inferior fiber based on the surface characterization of bamboo. Scanning electron microscope (SEM) images showed that the HWP made the fibers' structure loose and porous. Both pore volume and specific surface area were increased significantly after HWP, by 260.00% and 1804.76%, respectively. A decrease in pulp brightness was mainly due to the formation of new chromophore groups during the HWP process. The results of 13C nuclear magnetic resonance spectroscopy (13C-NMR) illustrated that some structures of milled wood lignin (MWL), such as guaiacyl, etherificated guaiacyl, and aromatic units, were increased during the HWP process. However, some lignin-links units of α-O-4, β-O-4, and some carbohydrate structures such as xylan, α- and β-glucose, and β-and β-mannose in lignin-carbohydrate complex (LCC) were evidently degraded. Additionally, most of the lignin and LCC were degraded under the simulative conditions of HWP bamboo. Furthermore, the analysis of UV spectrophotometry indicated that HWP was conductive to the generation of chromophore groups such as conjugated carbonyl, catechol, and o-benzoquinone.

Evaluation and Optimization of Kraft Delignification and Single Stage Hydrogen Peroxide Bleaching for Ethiopian Sugarcane Bagasse

ABSTRACT The current study investigated the Ethiopian sugarcane bagasse during its delignification using the Kraft pulping process and bleaching by single stage hydrogen peroxide process. The multilevel categoric experimental design was used to appraise the effects of the independent process variables (temperature, NaOH concentration, and time) on the pulp yield and kappa number during the Kraft pulping process. The central composite experimental design of response surface methodology was used to appraise the effects of independent bleaching variables (bleaching temperature, H2O2 concentration, and time) on the pulp yield, brightness, and whiteness during the bleaching process. The optimal pulp yield was 38.41% with 17.68 kappa number. The bleached pulp yield for the pulp with kappa number of 17.68 and the pulp with kappa number of 8.41 were 84.12% and 83.91%, respectively. The brightness and whiteness for the pulp with kappa number of 17.68 were 61.92% and 85.36%, respectively. Similarly, for the pulp with a kappa number of 8.41, the brightness and whiteness were 68.35% and 91.43%, respectively. Paper from the pulp with kappa number of 17.68 has higher tensile, burst, and tear strength. The study shows the promising utilization of the Ethiopian sugarcane bagasse for paper production via the Kraft delignification and single stage hydrogen peroxide bleaching.

Bio-pulping: An energy saving and environment-friendly approach

AbstractPretreatment of wood or other raw material with white-rot fungi (WRF) prior to pulping is known as biopulping. Lignin and hemicelluloses are removed selectively during early growth of WRF that produces enriched cellulose, known as selective delignification. Biopulping is considered as environment-friendly and cost-effective approach for delignification of lignocellulosic raw materials. The delignification efficiency of WRF during biopulping is directly related to ligninolytic enzymes production that is influence by several factors such as fungal strain, nature of raw material, oxygen availability, moisture content, pH, temperature, source of nitrogen, presence of Mn++and Cu++ions. The WRF, especiallyCeriporiopsis subvermispora,Trametes versicolorandPhanerochaete chrysosporium, have been used dominantly for the purpose of biopulping. It is an energy saving process that also improves brightness of pulp and strength properties including tensile index, burst index and folding endurance of paper. Significant decrease in kappa number has also been attained by fungal pretreatment of raw materials. Biological pretreatment of raw material also reduces the requirement of pulping chemicals.

Unbleached and bleached handsheet characteristics of Subabul heartwood and sapwood

Abstract The objective of this study was to understand the influence of bleaching on % residual lignin, water retention value, brightness and morphological properties of Subabul heartwood and sapwood pulps. The second aim was to compare the properties of unbleached and bleached handsheets with respect to tensile index and fractography. Screened wood chips of Subabul were subjected to kraft cooking (165 °C, 3 hours) followed by ECF bleaching and refining. When unbleached handsheets were compared, higher tensile index was found for sapwood sheets (29.8 N.m/g) than heartwood sheets (12.8 N.m/g). Therefore, it is recommended to use unbleached sapwood sheets for packaging grade applications. The bleached pulps have exhibited negligible residual lignin (0.1 %), higher water retention value (∼21) and higher brightness (88 %) compared to unbleached pulps. Subsequently, the bleached heartwood sheets revealed higher tensile index (∼7 fold) and higher modulus of elasticity (∼2.7 fold) compared to unbleached heartwood sheets. For printing grade applications bleached sapwood and bleached heartwood pulps are equally recommended, because no differences were observed in their pulp and sheet characteristics.

Physicochemical Characteristics of Fungal Xylanases and their Potential for Biobleaching of Kraft and Non-wood Pulps

Xylanases are enzymes with a wide variety of biotechnological applications, such as in the bioconversion of lignocellulosic materials, improvement of feed digestibility, and bleaching kraft pulps to increase pulp brightness. Many studies have been conducted and published over the years on cellulose pulp bleaching due to the need to search for more sustainable tools and thus reduce environmental pollution. Thus, in this review, we focus on analyzing the biochemical properties of xylanases produced by mesophilic and thermophilic fungi that have been used in the bleaching processes of kraft and non-wood pulps. Eucalyptus kraft pulp is still one of the most used raw materials in the production of pulp and paper, while straw and bagasse are alternative sources of non-wood pulps. Thermophilic fungal xylanases show optimum enzymatic activity at high temperatures and a shorter treatment period when compared to mesophilic xylanases in the bleaching step. However, mesophilic fungal xylanases exhibit a longer period of enzymatic treatment but achieve a satisfactory brightness and kappa number. Hence, these approaches will contribute to future applications of these xylanolytic enzymes in pulp and paper industries.

Bleachability improvement of eucalypt mechanical pulps using hydrogen peroxide in ethanol-water media

Alkaline darkening has a negative effect on chemimechanical pulps produced from various eucalypt chips. For instance, the pulp’s brightness has been found to drop rapidly when alkali addition exceeds its optimum amount. Therefore, to compare the effects of different media on brightness gain, eucalypt mechanical pulps were bleached using a typical peroxide bleaching sequence in a water medium and in an ethanol-water (E/W) medium. Various pulp brightness levels and changes of residue chemicals in the spent bleaching liquors were investigated. Compared to water medium, the net brightness gain notably increased when using the E/W medium at the same chemical dosages. The rate of pulp brightness loss caused by increasing alkali dosage dropped in the E/W medium. Analyses based on ultraviolet-visible diffuse reflectance spectra of bleached pulps, as well as gel permeation chromatography and pyrolysis-gas chromatography-mass spectrometry spectra of the residues in the spent bleaching liquors, indicated that the contributions to brightness improvement from ethanol-water media could be explained by the selective dissolution and removal of phenolic- or guaiacyl-structured lignin fragments that result in the formation of chromophoric groups under alkaline conditions.

Staged alkali and hydrogen peroxide treatment of poplar chemi-mechanical pulp

In order to improve the physical properties and brightness of poplar chemi-mechanical pulp, a new staged alkali and hydrogen peroxide treatment method was proposed and applied. Wood chips were impregnated and swelled with an alkali solution and then treated with a hydrogen peroxide bleaching liquor. A thorough evaluation and comparison of the physical properties and brightness of the pulps that underwent different treatment methods was conducted. The results showed that when the pulp was treated with an alkali and hydrogen peroxide treatment method with an alkali dosage of 6% and a hydrogen peroxide dosage of 6%, the tear index was 3.64 mN‧m2/g, the tensile strength was 3.61 kN/m, and the pulp brightness was 67.1% (ISO). The obtained physical properties and brightness of the alkali and hydrogen peroxide method treated pulp were greater than the traditional alkaline hydrogen peroxide method values, as well as the values of any other single treatment methods.

Oxalate formation during ClO2 bleaching of bamboo kraft pulp

Abstract This study aimed to investigate the oxalate formation mechanism during chlorine dioxide ( ClO 2 {\mathrm{ClO}_{2}} ) bleaching of bamboo kraft pulp, and thus explore favourable ClO 2 {\mathrm{ClO}_{2}} bleaching conditions to better control oxalate formation. The amount of oxalate formed varied linearly with ClO 2 {\mathrm{ClO}_{2}} dosage within the whole research range, while it rose exponentially within the first 90 mins of pulp bleaching. Then the actual bleaching process was simulated by reacting ClO 2 {\mathrm{ClO}_{2}} with three representative lignin model compounds and comparatively studied. The rule of oxalate formation in the simulated reaction system was identical to that in pulp bleaching by ClO 2 {\mathrm{ClO}_{2}} , except for oxalate production by veratraldehyde with prolonged reaction time. Under identical conditions, vanillin formed the highest amount of oxalate, while veratraldehyde formed the least. Furthermore, the amount of oxalate formed increased by 19.59 mg/kg when the kappa number of the delignified pulp was reduced by one unit. Considering the satisfactory pulp brightness and decreased oxalate formation, the recommended conditions for ClO 2 {\mathrm{ClO}_{2}} bleaching of bamboo kraft pulp were a ClO 2 {\mathrm{ClO}_{2}} dosage of 4 %, 60 °C and 70 mins.

Horseradish and potato peroxidase biobleaching of mixed office waste paper

Mixed office waste (MOW) pulp was biodeinked with crude enzyme extracted from Penicillium citrinum NCIM-1398. Crude enzyme dose was charged having activities of endo β-1,4-glucanase 6I U/g, xylanase 876.19 IU/g, and amylase 26.53 IU/g. The present study aimed to bleach the biodeinked MOW pulp with 3% H2O2 in the presence of a stabilizing agent viz. 0.1% ethylenediaminetetraacetic acid (EDTA) and 0.1% magnesium sulfate (MgSO4), which improved the pulp brightness up to 4.2% and the ERIC value was reduced by 24.1%. The residual H2O2 left in the pulp slurry after bleaching was subjected to peroxidase treatment using enzyme dose 0.017 U/g at 20 °C for 3 h at 200 rpm. Horseradish peroxidase reduced residual H2O2 in the pulp slurry from 0.30 to 0.05 g/L and improved the brightness of pulp to 88.1%, while the ERIC value was reduced by 20.9%. Potato peroxidase reduced residual H2O2 from 0.30 to 0.04 g/L, reduced the ERIC value by 30.9%, and improved the brightness to 89.2%. Peroxidase treatment was not only observed to consume the residual hydrogen peroxide left after the bleaching stage but also may come up as eco-friendly technology to recycle MOW paper as writing printing grade paper.

Pretreatment of Chlorine Dioxide Solution for Pulp Bleaching

Adsorbable organic halogen (AOX) is mainly produced by the reaction of residual lignin and chlorinated bleaching agents during bleaching processes. The formation of AOX can be reduced via optimization, addition of chemical additives, and/or pretreatment processes. Only a few studies exist on the effective purification of chlorine dioxide solutions and its effect on AOX reduction. In this paper, the effects of the extraction pressure, temperature, pH, and extraction time on the chlorine gas removal rate (CR) were evaluated. In addition, a response surface model was established to optimize the chlorine gas removal. The temperature of chlorine gas separation was optimized at 39.85 °C, with a separation pressure of –51.20 kPa and solution pH of 1.94, providing an estimated CR of 70.93% under the optimum separation conditions. Chlorine dioxide solutions with and without chlorine gas removal were used for pulp bleaching. AOX formation was reduced by 69.57% at the same 2.0% chlorine dioxide dosage, while the pulp brightness decreased by 3.0%ISO. In addition, AOX formation was reduced by 27.90% at the same bleached pulp brightness (80.00%ISO). The results provide theoretical support for the production of high-purity chlorine dioxide solutions and the development of clean pulping and papermaking processes.