Bleached Softwood Kraft Pulp Research Articles

Enhanced wet tensile paper properties via dielectric-barrier discharge

Abstract Dielectric-barrier discharge treatment was used to modify fully bleached softwood kraft and unbleached softwood thermomechanical pulp handsheets. The effect of dielectric-barrier discharge treatment on the physical strength properties and dimensional stability of handsheets were analyzed. Increased dielectric-barrier discharge treatment power resulted in significant increases in the wet tensile index of handsheets. Increases in the surface acid content of pulp fibers do not appear to contribute to changes in paper properties, nor do changes to relative bonded area within handsheets. Enhanced wet strength via dielectric-barrier discharge treatment corresponds to increased dimensional stability. This appears to be due to fiber cross-linking in the case of bleached kraft pulp, since the wet-strain decreases as wet tensile and wet Young's modulus increase. In the case of unbleached thermomechanical pulp, the wet-strain shows no decrease, yet the wet Young's modulus increases as the wet tensile index increases.

Pulp charge determination by different methods: effect of beating/refining

Total and surface charge of unbleached and bleached softwood kraft pulps of different levels of freeness were determined using three different techniques—potentiometric titrations, conductometric titrations (with NaOH and NaHCO 3 separately) and polyelectrolyte titrations using a particle charge detector (PCD). Each method gave different charge values but the relative levels were similar for each pulp. The surface charge as determined by titration with poly-DADMAC was highly dependent on the degree of beating but the total fibre charge as given by potentiometric titration or conductometric titration with NaOH remained constant after beating. Conductometric titration with sodium hydroxide gave a slightly higher value for total charge than the potentiometric titration. Conductometric titrations with 0.05 M NaOH gave higher values of pulp charge than similar titrations with 0.05 M NaHCO 3.

Carbon-13 NMR evidence for cocrystallization of cellulose as a mechanism for hornification of bleached kraft pulp

Solid-state 13C NMR spectroscopy was used to characterize a bleached softwood kraft pulp in the never-dried state and after cycles of drying and remoistening. Changes in NMR signal strengths indicated that growth of crystalline domains involved cocrystallization rather than accretion of cellulose from noncrystalline domains. A cluster of C-4 signals at 89.4 ppm, assigned to the interiors of crystalline domains, grew at the expense of C-4 signals at 84.0 and 84.9 ppm, assigned to the well-ordered surfaces of crystalline domains. Irreversible changes were not detected until the moisture content dropped below 18%. They were enhanced by a second drying/remoistening cycle, but showed little further change on subsequent cycles. The necessary conditions resembled those reported for hornification, suggesting that cocrystallization might provide a mechanism for hornification.

Influence of Fiber Properties on the Network Strength of Softwood and Hardwood Kraft Pulp Fibers from Different Stages of a Bleaching Sequence

During chemical pulping and bleaching operations, fiber properties are gradually changed due to mechanical and chemical treatment. The changes in fiber properties, in turn, influence network strength, i.e., the rigidity of fiber networks. In this study, the influence of fiber length, lignin content, specific surface area, total charge, and fiber flexibility on the network strength of commercial unbleached and totally chlorine free (TCF) bleached (ozone and hydrogen peroxide) softwood and hardwood kraft pulp suspensions have been investigated. The fiber length, total lignin content, and total charge decreased together with the network strength along the fiber line while the specific surface area and fiber flexibility increased. Correlations equal to or greater than 90% were found between network strength and fiber length, lignin content, specific surface area, and total charge. The interrelationship between the fiber properties indicated that for a given pulp, the total lignin content was the parameter that had the greatest influence on the network strength.

The Role of Alkali-Hydrogen Peroxide during Pulp Treatment

Semi-quantitative method was developed for the determination of α-carbonyl structure in solid lignin. Deuteride reduction followed by nitrobenzene oxidation was applied to oxygen bleached softwood kraft pulp (NOKP) in order to evaluate the reactivity of hydrogen peroxide with α-carbonyl structures in lignin. We already showed that hydrogen peroxide attacked α-carbonyl structures in lignin very clearly during milled wood lignin treatment. However, when NOKP and hydrogen peroxide treated NOKP were analyzed by this method, the role of hydrogen peroxide was not clearly observed in terms of the content α-carbonyl structure. By the analysis of alkali treated NOKP without hydrogen peroxide, it was suggested that, at the hydrogen peroxide treatment, the effect of hydrogen peroxide on the α-carbonyl structure might be hidden by the generation of α-carbonyl structure and that actually hydrogen peroxide effectively degrades those newly produced structures. Hydrogen peroxide was found to play such a “hidden role” not only for newly produced α-carbonyl structures but also for the newly produced permanganate consuming substances during the treatment.

The effects of xyloglucan on the properties of paper made from bleached kraft pulp

Xyloglucan was adsorbed onto bleached soft-wood kraft pulp followed by preparation and analysis of handsheets with respect to sheet formation as well as sheet mechanical and optical properties. Adsorption of xyloglucan was found to be slow. After more than 20 hrs adsorption, equilibrium had not been reached. The amount of xyloglucan adsorbed increased with beating, but neither the rate of adsorption nor the quantity adsorbed was significantly affected by temperature. Xyloglucan was found to be practically irreversibly adsorbed onto the fibres and the effects of xyloglucan on paper sheet properties were investigated after thorough washing of the pulp. The adsorption characteristics of xyloglucan confirm observations by other authors on other cellulose substrates. Tensile index values for handsheets formed with the xyloglucan-containing pulps were higher than those measured for control pulps with a comparable beating degree. The light scattering coefficient was, however, not affected by xyloglucan adsorption. Hence, the increase in tensile strength is attributed to an increased relative bond strength between the fibres. Tensile strength versus tear strength relationship was similar for pulps with and without xyloglucan, but water retention value and dewatering resistance were lower for the xyloglucan treated pulps than for the reference pulps at the same tensile strength. In addition, formation was improved for pulps with adsorbed xyloglucan. The conclusion is that xyloglucan is a promising wet end additive that decreases the necessity for beating of the pulp and improves the formation of paper.

ACTION OF OXYGEN ON THE CARBOHYDRATES OF A KRAFT PULP. THE INFLUENCE OF A SODIUM BOROHYDRIDE PRE-TREATMENT

A fully bleached softwood kraft pulp was chosen as a model for pulp carbohydrates. The pulp was submitted to oxygen bleaching stages, to study the action of oxygen upon carbohydrates in the absence of lignin. The pulp was not degraded under mild conditions. In the presence of several metal ions, the carbohydrates were severely degraded by oxygen. Under these conditions, intermediate HO· radicals were detected. The results suggested an additional pathway to the classical mechanism proposed in the literature. The influence of a pulp pre-treatment with sodium borohydride was studied, and the origin of its protective effect during oxygen bleaching was demonstrated.

Fiber yield for fully bleached kraft pulps from black locust ( Robinia pseudoacacia ) and silver maple ( Acer saccharinum )

) and silver maple (Acer saccharinum) with emphasis being placed on fiber yield. Black locust had longer fibers, a higher Seifert cellulose content, and a lower lignin content compared to the maple. The results were higher strength and bleached pulp yield for the black locust. The final yields were 49.5% for black locust and 47.7% for maple. These values are significantly higher than the 40–42% that is normally obtained for bleached softwood kraft pulps.

Application of an Exponential Kinetic Equation to the Interaction of Optical Brighteners with Pulp

A bleached softwood kraft pulp was treated with fluorescent whitening agentsTinopal UP and Leucophor AP under different conditions. The kinetics ofadsorption-chemical interaction between optical brighteners and pulp wasdescribed by an exponential kinetic equation. An entropy heterogeneity of thepulp surface related to the active sorption centers, their accessibility and theirspatial orientation was confirmed. The activation energy values obtained werefound independent of the brightener concentration and on the increase of pulpwhiteness. A decisive role of the entropy factors was ascertained.

Measurement of Elastic Constant of Pulp Fiber Wall by Scanning Acoustic Microscope

An acoustic micro-metrology technique of a scanning acoustic microscope, as acoustic material signature, was applied to measure the elastic constant of softwood bleached kraft pulp fiber wall. The Rayleigh wave speed measurement of cross sectional surface of heat-treated and untreated single softwood bleached kraft pulp fibers, which were 3, 520±170m/s and 3, 240±180m/s, respectively, was achieved by this technique. This evidently means that the wall of heat-treated fibers was stiffer than that of the untreated ones because the higher the Rayleigh wave speed, the higher the elastic constant (C44). Furthermore. if the ideal component of fiber wall is supposedly composed from a majority of a transversely isotropic S2 layer, the calculation of C44of the fiber wall could possibly be demonstrated by applying a Rayleigh wave speed to shear wave speed ratio of 0.93 and a density of 1.5g/cm3for a close-packed cellulosic material of the S2layer according to the theoretical equation. The calculated C44 values for the heat-treated and untreated fiber wall were 22±2 GPa and 18+2 GPa, respectively. However, handsheets made from unbeaten heat-treated fibers had a lower in-plane shear modulus than those from unbeaten unheated fibers. These results indicate the effect of heat treatment on elasticity of a fiber wall which is generally known as hornification.

Alternative Measurements of Productive Efficiency in the Global Bleached Softwood Pulp Sector

Abstract In this article, we conduct a productive efficiency analysis using the two major methods: stochastic frontier analysis (SFA) and data envelopment analysis (DEA). First, we demonstrate the steps and assumptions involved in SFA and DEA, and highlight their strengths and weaknesses. Then we apply them to the case of bleached softwood kraft pulp production to derive technical and allocative efficiency measures for 102 mills in the world. We find that in general, the SFA cost-efficiency levels are higher than their DEA counterparts, and much of the cost inefficiency is caused by inappropriate input mix, or allocative inefficiency, instead of the way with which inputs are converted into outputs, or technical inefficiency. In addition, SFA and DEA results rank some of the producers in different orders. We also find that while cost-efficiency levels vary in different regions, most producers have substantial opportunities to make improvements. Finally, we discuss implications of our study. FOR. SCI. 46(4):558–569.

Biomechanical pulping: a mill-scale evaluation

Mechanical pulping process is electrical energy intensive and results in low paper strength. Biomechanical pulping, defined as the fungal treatment of lignocellulosic materials prior to mechanical pulping, has shown at least 30% savings in electrical energy consumption, and significant improvements in paper strength properties compared to the control at a laboratory scale. In an effort to scale-up biomechanical pulping to an industrial level, 50 tons of spruce wood chips were inoculated with the best biopulping fungus in a continuous operation and stored in the form of an outdoor chip pile for 2 weeks. The pile was ventilated with conditioned air to maintain the optimum growth temperature and moisture throughout the pile. The control and fungus-treated chips were refined through a thermomechanical pulp mill (TMP) producing lightweight coated paper. The fungal pretreatment saved 33% electrical energy and improved paper strength properties significantly compared to the control. Since biofibers were stronger than the conventional TMP fibers, we were able to reduce the amount of bleached softwood kraft pulp by at least 5% in the final product. Fungal pretreatment reduced brightness, but brightness was restored to the level of bleached control with 60% more hydrogen peroxide. The economics of biomechanical pulping look attractive.

The effect of Trichoderma cellulases on the fine structure of a bleached softwood kraft pulp

The mode of action of several Trichoderma reesei cellulase preparations was investigated in relation to their effect on the crystallinity and degree of polymerization of a fully bleached softwood kraft pulp. One complete (Celluclast 1.5L, Novo Industri) and six modified cellulases (Rohm Enzyme Finland Oy, former Primalco Ltd. Biotec) were used under a relatively low enzyme loading of 40 mg protein g −1 cellulose in a reaction mixture in which an excess of exogenous cellobiase activity was added (Novozym 188). This enzyme loading was used to assess the mode of action of the enzymes under both non-saturating and non-inhibitory conditions. The modified cellulase preparations were obtained from T. reesei by deleting the following components of the cellulase system: EG I and/or EG II or CBH I and/or CBH II. Characterization of hydrolysates by gel permeation chromatography (GPC) showed that short incubation times of 4 h with CBH I-deficient enzymes (CBH I− and CBH I/II−mutants) resulted in the highest shifts in the molecular weight distribution of cellulose. Compared to EG-deficient enzymes (EG I−, EG II− and EG I/II−mutants), the lack of CBH II resulted in equivalent changes in both polydispersities and average degrees of polymerisation of cellulose. This suggested that the role of CBH II in hydrolysis was similar to that of both endoglucanases I and II. The effectiveness of all mutant enzymes in hydrolysing cellulose was much lower than that obtained when a complete cellulase system such as Celluclast 1.5L was used. Our results also indicated that the lack of CBH I was very detrimental to hydrolysis and depolymerization of cellulose and that EG I has a greater effect on the substrate than EG II. However, there were no detectable changes in the degree of crystallinity of partially hydrolysed pulps, regardless of the enzyme system used.

Flow properties of microcrystalline cellulose suspension prepared by acid treatment of native cellulose

The properties of cellulose microcrystals and their colloidal suspensions obtained by acid treatments of native cellulose have been investigated. Bleached softwood kraft pulp was treated with 65% (w/w) sulfuric acid or 4 N hydrochloric acid and the resulting particle morphology and flow properties of the aqueous suspensions were studied. Colloidal dispersion of the HCl-treated sample was obtained by more thorough removal of acid from the hydrolysate than in the case of H 2SO 4 treatment. The H 2SO 4-treated and HCl-treated samples had similar particle sizes and shapes when observed by electron microscopy. Conductometric titration of suspensions revealed that the H 2SO 4-treated sample had a surface charge of 84 m-equiv kg −1 dry material due to the introduction of sulfate groups, while that of the HCl-treated sample was undetectable. The H 2SO 4-treated suspension showed no time dependence in viscosity, while the HCl-treated suspension was thixotropic at concentrations >0.5% (w/v) and anti-thixotropic <0.3%. The inclination of the relative viscosity–concentration plot (Einstein coefficient) for the H 2SO 4- and HCl-treated suspensions were 135 and 1380, respectively. The former value, when used in Simha's equation for rod-like particle suspension, roughly corresponds to an axis ratio of 50 estimated from the micrographs.

低ＡＯＸ，高白色度パルプ製造における過酢酸の新利用技術

The effects of chelating agents, peracetic acid and alkaline peroxide on the replacement of chlorine dioxide and hypochlorite in D-Eo-H-D bleaching of oxygen delignified hardwood kraft pulp were studied in a laboratory scale. Since an increased use of peroxygen chemicals necessitates a use of a chelating agent, both DTPA and a new chelating agent with low nitrogen content (DEAS) were tested. Peracetic acid was used here as a bleaching agent in combination with chlorine dioxide in a D2 stage. Also the effect of peracetic acid on post-bleaching of O-D-EOP-D bleached softwood kraft pulp was studied.The bleaching experiments indicate that the importance of a chelation prior to Eo stage increases with the decreasing active chlorine charge in the D1 stage and increasing peroxide charge in the E. stage. With a sequence of Q/D-EOP-Q/D/PAA the total active chlorine charge in D-Eo-H-D dropped from 48 kg act. C1/tp to 20 kg act. C1/tp by using 10 kg H2O2/tp in the E0 stage and 5 kg peracetic acid/tp in the D2 stage. Also 8 kg hypochlorite/ tp were eliminated at the same time. The use of DEAS in the Q/D stage gave more improved pulp properties for bleached pulp than the use of DTPA correspondingly.

Normal Pressure Pulping of Jute, Kenaf and Mesta Bast Fibers.

To develop a simple pulping technique for small scale papermaking, a combination of ammonium oxalate pretreatment and alkaline hydrogen peroxide treatment at normal pressure was examined for jute, kenaf and mesta bast fibers. The ammonium oxalate pretreatment seems sufficient to remove transition metal ions (Mn, Fe and Cu) and a part of Ca and Mg to give a favorable metal profile for the second alkaline hydrogen peroxide pulping. The brightnesses of the pulp samples were about 60_??_70% at 5% H202 dosage although kappa numbers were still high. The strength properties of the pulps were comparable with those of commercial softwood bleached kraft pulp except folding endurance. The pulps may have strength properties enough for some practical use in local pulp mills.

Chlorophenanthrenes, alkylchlorophenanthrenes and alkylchloronaphthalenes in kraft pulp mill products and discharges

Chlorinated phenanthrenes (PCPHs; P=1–5), alkylphenanthrenes (C 4-PCPHs; P=1–3), dimethylnaphthalenes (C 2-PCNs; P=1–4) and trimethylnaphthalenes (C 3-PCNs; P=1–2) were analyzed by high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) in pulp, effluent and biosludge of two kraft pulp mills (mills 1 and 2). These compounds were indicated to be formed in the manufacture of both bleached hardwood and softwood kraft pulp. Different compound groups dominated in mill 1 samples compared to mill 2 samples. Differences between birch and pine pulp from mill 1 were observed for all substance groups but in mill 2 pulp only for PCPHs. The highest concentrations of PCPHs in pulp (3 ng/g dry weight) were measured in pine pulp from mill 2. PCPHs occurred at a higher level in pine pulp compared to birch pulp. The sum levels of C 4-PCPHs in pulp ranged from 0.9 to 8.7 ng/g dw, those of C 2-PCNs from 0.7 to 8.2 ng/g dw and those of C 3-PCNs from 0.3 to 4.5 ng/g dw. Drying and pressing of pulp to sheets seemed to effect on the amounts of extractable C 4-PCPHs in pulp, because concentrations measured in dried sheet pulp were lower than in wet pulp slurry. Mill 2 biosludge had C 4-PCPHs (61 ng/g dw) at a higher level than C 2-PCNs (35 ng/g dw). In mill 1 biosludge these groups were at a similar level (72 ng/g dw). The sum concentration of C 3-PCNs in mill 1 sludge was 47 ng/g dw and in mill 2 sludge 16 ng/g dw. All studied groups were found both as particle-bound and dissolved in filtrates. Total levels in effluents ranged from 2 ng/L for C 3-PCNs in mill 2 effluent to 56 ng/L for C 4-PCPHs in mill 1 effluent.

Dynamic Wettability on Pulp Fiber and Paper Surface (Part 1). Measurement on Wettability of Pulp Fiber at Short Time Intervals.

An optical technique to measure directly the contact angle of liquid against a single wood-pulp fiber has been developed for characterizing fiber-liquid interactions. A fiber was contacted with liquid by partially immersing the fiber in a drop of the liquid. The contact angle was determined from a series of photographs of the liquid drop silhouette at the point of contact. The contact line and profile history were continuously photographed in every 0.2 seconds after the initial contact. The direct contact angle measurement was carried out by a system consisting of an automatic rewinding camera with two bellows, an intervalometer and a stroboscope. Contact angle of a water drop on handsheet surface were also measured as a function of time according to that for single pulp fibers. The measurement on single pulp fibers by this technique did not deviate significantly from data previously reported by the wilhelmy method. Because of appropriate reproducibility with small standard deviation, this technique was considered to be suitable for measuring the contact angle on fibers of small cross section. Contact angle of water on single pulp fibers showed a rapid decrease with time in the initial 1 second and then was settled after 5-15 seconds.Softwood bleached kraft pulp fiber and its handsheet showed fairly low contact angle of water.On the other hand, contact angle of single fiber and handsheet from thermomechanical pulp was higher. This can be interpreted as being due to higher lignin and extractives content. For softwood bleached kraft pulp fiber, water showed lower contact angle compared with methylene iodide. But there was little difference between water and methylene iodide in case of thermomechanical pulp fiber. In order to determine surface properties of single pulp fiber of kraft and thermomechanical pulps, the dispersion and polar components to the surface free energy were calculated. The similar values for the dispersion component were obtained, whereas the polar component of kraft pulp fiber was greater compared with thermomechanical pulp.

Effect of Various Treatments on Wettability of Pulp Fiber.

Influences of various treatments of pulps, such as beating, recycling, sizing and solvent extraction, on dynamic wettability of single pulp fiber and a handsheet from the pulp fiber were discussed from the measurement of contact angle to water at short time intervals.Beating had little influence on contact angle of softwood bleached kraft pulp fiber and the handsheet.Recycling of the pulp was performed by a sequence of defibration, dewatering and drying at 80°C for 24 hours five times repeatedly. Remarkable increase in contact angle of kraft pulp fiber was observed. Also recycling caused delay in the rate of decrease of contact angle of the fiber with time. On the other hand, contact angle of the handsheet decreased with repetition times of recycling.Extraction of thermomechanical pulp with atcoholbenzene was fairly effective on decrease in contact angles of both single fiber and handsheet.Sizing with alkylketene dimer increased contact angle of kraft pulp fiber, but there was no significant difference in contact angle when the amount of sizing agent added were varied from 0.05 to 0.17% . However, contact angle of the handsheet much increased with sizing.

Changes in zeta potentials of amorphous cellulose particles with aluminum sulfate.

Microcrystalline cellulose powder, linter cellulose, softwood bleached kraft pulp (SBKP), and hardwood bleached kraft pulp (HBKP) were converted to amorphous particles, and ζ-potentials of suspended samples were measured with the addition of aluminium sulfate (alum). ζ-Potentials of these samples without alum were related to their carboxyl content, and the sample with higher carboxyl content has the more negative ζ-potential. In the presence of alum in suspensions, ζ-potentials are influenced not only by carboxyl content but also swelling degrees of samples. When amorphous samples with different swelling degrees were prepared from microcrystalline cellulose powder, the amorphous sample with higher swelling degree had the more negative ζ-potential. ζ-Potentials of amorphous particles prepared from linter cellulose, SBKP, and HBKP were shifted to positive direction by the addition of alum to suspensions, but never turned to positive over the wide range of alum addition. ζ-Potentials of amorphous particles prepared from linter cellulose, SBKP, and HBKP were almost unchanged at least for one day, during standing of suspensions at room temperature after the addition of alum. In contrast, ζ-potentials of microcrystalline cellulose powder and those of amorphous particles prepared from microcrystalline cellulose powder were shifted to negative direction by standing of suspensions. These relaxation phenomena of ζ-potentials in the presence of alum may depend on structural changes of alum in suspensions during the standing.