Hardwood Kraft Pulp Research Articles

Mechanical and Hygroscopic Properties of Molded Pulp Products Using Different Wood-Based Cellulose Fibers.

With an increasing interest for molded pulp product (MPP) in the industry, it is important to fully understand how the manufacturing process is different from papermaking. One specific way to differentiate the processes is to compare their resulting products. As the paper industry uses several wood fibers with various pulping processes, it is interesting to compare some of these fibers, to further progress our understanding of the MPP process. In this study, six different wood fibers were used (as received) and analyzed to obtain the sample with the lowest moisture uptake and highest tensile properties. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and fiber analysis module (MorFi) observations were performed, as well as moisture uptake measurements after sorption and tensile tests. We observed significant differences between the fibers tested. Kraft fibers (bleached softwood kraft pulp (BSKP), bleached hardwood kraft pulp (BHKP), and unbleached softwood kraft pulp (USKP)) showed smoother surfaces and less non-cellulosic molecules, such as hemicellulose, lignin, and pectin, in the SEM images. Bleached chemi-thermomechanial pulp (BCTMP) and recycled pulps (R-NPM and R-CBB) both showed non-cellulosic molecules and rougher surfaces. These results were confirmed with the FTIR analysis. With kraft fibers, MPP mechanical properties were lower than non-kraft fibers. Resulting moisture uptake is in between the recycled fibers (lowest moisture uptake) and BCTMP (highest moisture uptake). The removal of non-cellulosic molecules reduces the mechanical properties of the resulting MPP. The incorporation of non-wood molecules, as found in recycled fibers, also reduces the mechanical properties, as well as moisture uptake, when compared with BCTMP.

Effect of Pulp on the Strength of Coloring Paper Used for the Production of Fruit Bags

In the present study, we explored an eco-friendly method for improving the strength of base paper for fruit bags. We determined the fibers characteristics of hardwood bleached kraft pulp (HwBKP), recycled liquid crystal display glass interleaf (LCD), and old newsprint (ONP), which are raw materials used to produce coloring paper. Using various types and mixing ratios of pulp, we produced coloring paper handsheets and determined their strengths. The HwBKP had the highest initial freeness, and as the freeness decreased, the strength of the handsheet increased. The ONP had the lowest initial freeness and paper strength owing to a high recycling rate. The LCD interleaf comprised softwood fibers and was stronger than a handsheet with a Canadian Standard Freeness (CSF) value of 450 mL made from HwBKP. However, when the freeness of HwBKP was 350 mL CSF, the handsheet strength decreased as the mixing ratio of LCD interleaf increased. Therefore, we concluded that it was necessary to decrease the freeness of HwBKP or increase the mixing ratio of LCD interleaf while maintaining the freeness of HwBKP at 400-450 mL CSF to enhance the strength of coloring paper.

Quality Evaluation of Cellulose Nanofiber Manufactured with a Prototype Grinder for the Development of a Taylor-Flow Nanogrinding System

In this study, we aimed to develop a domestic grinder for the production of cellulose nanofibers (CNFs). Therefore, we manufactured a prototype grinder using Taylor-flow nanogrinding technology and evaluated the quality of the CNFs produced using it. To produce the CNFs, we pretreated hardwood bleached kraft pulp (HwBKP) with 0.5% or 1.0% of an enzyme. The enzyme-pretreated CNFs (EN-CNFs) were produced using the prototype grinder, and their particle size, viscosity, and fiber width were measured. As a control, EN-CNFs were also prepared with an imported microgrinder under the same conditions used for the prototype grinder and the same physical properties were investigated.<BR>With regard to the prototype grinder, as the grinding time increased, the particle size and fiber width decreased, and the viscosity increased. The imported grinder showed the same trends. Based on the fiber width of the EN-CNFs, the CNF manufacturing performance of the prototype grinder was judged to be 41.3% of that of the imported grinder. We drew the following conclusions based on our analysis of the fiber width and the difference in design between the two grinders: The effective method for improving the grinding efficiency of a domestic Taylor-flow nanogrinder should be developed by studying the particle size of the diamond coating electrodeposited on the cylinder surface, the gap between the fixed cylinder and the rotating cylinder, and the efficiency of the cooling process.

H2O2 bleaching of brown pulp with adsorbed xylan and its modifying effects on the mechanical properties of paper

Xylan is the primary hemicellulose in most hardwood species, especially in birch. Research has highlighted the exploitation of xylans as a strength-enhancing additive to paper due to the current trend for the effective utilization of biomass. In this paper, a new pulping process was proposed, which involved the extraction of xylan prior to pulping, followed by the re-adsorption of the pulp after the final stage in the digester, followed by a suitable bleaching process. The aim of this work was to bleach hardwood kraft pulp (brown pulp) with adsorbed birch xylan via hydrogen peroxide and study the effect of the bleaching parameters on the paper properties. The results showed that the optical properties of paper decreased; however, the mechanical properties increased after the brown pulp adsorbed birch xylan. During the bleaching process, better mechanical properties were obtained with shorter bleaching times and lower bleaching temperatures, initial pHs, and MgSO4 dosages. However, the optical properties were improved as the bleaching time, temperature, initial pH, and MgSO4 dosage were increased. The adsorption of birch xylan could effectively modify the mechanical properties of paper made from brown pulp under various phases.

Understanding the evolution of cellulose fibers during enzyme treatment

Enzyme treatment is a potential strategy for producing cellulose fibrils but its evolution of the mesoscopic and microcosmic structures is not fully understood. In this work, the effect of the properties and microstructures of cellulose bleached hardwood kraft pulp (BHKP) subjected to different enzyme treatment times (0−10 h) on further fibrillation was explored by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results showed that the enzyme treatment did not change the crystal structure of cellulose but destroyed the intermolecular and intramolecular hydrogen bonds, leading to the increase of the crystal index and size. A thorough investigation on the relation between treatment and evolution of inter-/intra-molecular H-bonds in cellulose including content and cleave sequence of H-bonds was conducted by FTIR peak fitting, second derivative analysis and generalized two-dimensional correlation spectroscopy (2DCOS). Compared to intramolecular H-bonds, the intermolecular H-bonds was first broken with a significant decrease in content. In addition, enzyme treatment could promote the peeling of fibrils, and various properties such as yield, water retention value, aspect ratio, and degree of polymerization, etc. were gradually reduced over time relative to the original material, these discoveries provide a theoretical support to a more effective treatment method for the commercial production of cellulose fibrils.

Effect of Polyelectrolyte-Cationized Cellulose Nanofibril on the Properties of Paper

In this study, the effect of a cationic cellulose nanofibril (CNF), produced by combining surface-modification using cationic polyelectrolyte and micro-grinding, on the strength of paper, was evaluated. Hardwood bleached kraft pulp (HwBKP) was pretreated with poly-DADMAC, and then a method of previous study was conducted, followed by micro-grinding. Afterward, the zeta-potential and fiber width of the untreated and cationic CNFs were measured. The handsheets were produced by adding the untreated and cationic CNFs into the furnish that was prepared with HwBKP and softwood BKP (SwBKP), after which their physical properties were evaluated. The drainage rate and chemical oxygen demand (COD) of the furnish were analyzed based on the addition of CNFs to identify the effect of cationic CNF on the drainage and retention at the wet-end part.<BR>Further, the zeta-potential of the cationic CNF surface-modified with poly-DADMAC exhibited a positive value, but no significant difference was noted in the fiber widths based on the surface-modification. The cationic CNF exhibited higher tensile and burst indexes, and folding endurance because of higher retention at the wet-end part and higher fiber bonds than that in the untreated CNF. However, the cationic CNF did not show the difference in the ISO brightness and opacity of the paper, and the drainage rate of the furnish from untreated CNF. Thus, it was concluded that the cationic CNF, produced via surface-modification using poly-DADMAC and micro-grinding, was more effective in improving the strength of the paper regarding the similar optical properties of the paper, as well as the drainage rate of the furnish, compared with untreated CNF.

How do xylanase and hot acid stages differ at enhancing elemental chlorine-free bleaching of hardwood kraft pulp?

Hardwood kraft pulp contains relatively high hexenuronic acid content which increases unnecessary consumption of bleaching chemicals and has negative effects on pulp brightness stability. Hexenuronic acid can be partly removed by an enzyme treatment or a hot acid treatment. The difference between enzyme and hot acid stages on removing hexenuronic acid and enhancing hardwood kraft pulp ECF bleaching has been investigated. A typical hot acid stage removed more than 60% of hexenuronic acid but only saved about 20% of chlorine dioxide to achieve 84% ISO, while xylanase treatment only removed 12% of hexenuronic acid but saved approximately 40% of chlorine dioxide to achieve the same brightness target. In addition to a slight reduction of hexenuronic acid, fiber ultrastructure analysis reveals that enzyme pretreatment removed hemicellulose layer which was originally present on the fiber surface. The removal of “barrier” xylan increases fiber accessibility to bleaching chemicals and decreases the diffusion resistance of delignification during bleaching.

Effect of polysulfide pulping process on the energy balance of softwood and hardwood kraft pulp mills

Abstract Polysulfide pulping is a method to increase the pulp yield in a kraft pulp mill. Higher production is in the core of pulp mill process development, but modifications in cooking raise questions on their effects on the other parts of the process. This study focuses on the impacts of polysulfide pulping on the energy use and production of kraft pulp mills. The impacts are estimated by calculating and analyzing the steam and electricity balances of reference softwood and hardwood mills. Energy generation using residual biomass is an essential part of the operation of a kraft pulp mill, and often a notable source of income. The results show that implementation of polysulfide cooking affects both energy consumption and production. Higher hemicelluloses content of pulp cooked using polysulfide liquor means that less organic material ends up in the black liquor. Subsequently, the recovery boiler energy production suffers. The reduced steam production together with increased steam consumption decreased electricity production, corresponding to a decline in sellable electricity of 22.4 % in the hardwood mill and 28.4 % in the softwood mill. The study shows that increasing the pulp production by investing in polysulfide cooking in stand-alone kraft pulp mills can be economically feasible.

Combining phosphotungstic acid pretreatment with mild alkaline extraction for selective separation of hemicelluloses from hardwood kraft pulp

In this study, a modified process, namely PTA-4%CCE, consisting of an initial phosphotungstic acid (PTA) catalytic hydrolysis, followed by a low-alkali cold caustic extraction (4%CCE) was investigated for upgrading a bleached hardwood kraft pulp to dissolving pulp via selectively removing hemicelluloses. The results showed that the PTA hydrolysis resulted in degraded hemicelluloses with low molecular weight and an increased fiber accessibility. These favorable changes of fiber morphologies facilitate the alkali penetration inward and hemicelluloses diffusion/removal outward even under a very low alkali concentration (4% NaOH) in the subsequent CCE stage (4%CCE), thus enabling a high hemicellulose removal selectivity (85.2%) while decreasing alkali usage. PTA also showed excellent recyclability/reusability with more than 86% recovery. The cellulose purity and reactivity of resultant pulp were 94.92% and 49.5%, respectively. This study reveals that the modified process provides a sustainable and effective strategy for hemicelluloses separation from cellulose fibers.

Converting bleached hardwood kraft pulp to dissolving pulp by using organic electrolyte solutions

In this laboratory study, a hardwood bleached kraft pulp (HBKP) was converted to dissolving pulp by removing hemicellulose using organic electrolyte solutions (OES), consisting of ionic liquid (1-ethyl-3-methylimidazolium acetate (EminAc)) and a polar organic solvent γ-valerolactone (GVL). The molar ratio of GVL/EmimAc, and temperature have significant effect on the swelling of HBKP fibers, thus the hemicellulose dissolution/removal process. Under the optimal conditions of GVL/EmimAc molar ratio of 4 and 60 °C, hemicellulose was effectively removed, leading to the formation of a dissolving pulp with yield of 76%, cellulose content of 91%, Fock reactivity of 56.8% and viscosity of 723 mL/g. Furthermore, the potential of using EmimAc/GVL/water ternary system to selectively remove hemicelluloses from the same HBKP was studied. The GVL/EmimAc/water ratio of 2:1:1 at 60 °C showed promising results, with yield of 76.7%, and cellulose content of 94.8%.

Effect of nanofibrillated cellulose made from enzyme-pretreated bamboo pulp on paper strength

The applicability of bleached bamboo kraft pulp (Ba-BKP) was explored as a raw material for the manufacture of nanofibrillated cellulose (EN-NFC) made of enzyme-pretreated pulps and the effects of the EN-NFC on enhancing paper strength. The Ba-BKP was pretreated using an endo-glucanase enzyme at 50 °C and pH 6, after which the EN-NFC was made by micro-grinding. Bleached hardwood kraft pulp (Hw-BKP) was used as a control, and the non-enzymatic refining pretreatment of BKPs was compared with the enzyme pretreatment. The EN-NFC was incorporated into handsheets, and the sheet strengths were measured. The physical properties of the NFC made from the Ba-BKP were similar to those made from the Hw-BKP. The NFC prepared following enzyme pretreatment were smaller and more uniform than those pretreated with refining. The EN-NFC made from the Ba-BKP was effective at enhancing tensile index by 52.7%, and burst index by 210.2% when 2% of EN-NFC was added in the furnish, and those of handsheets containing the EN-NFC made from Hw-BKP showed the similar improvement. Therefore, Ba-BKP can be used as a raw material for the manufacture of EN-NFC that confers similar physical properties and strength enhancement to paper as those made from Hw-BKP.

감나무 부산물로부터 제조된 셀룰로오스 나노피브릴의 물성 평가

In this study, we evaluated the applicability of fruit by-products as raw materials for the production of cellulose nanofibril (CNF). The persimmon byproducts generated by pruning persimmon trees were collected and used for the manufacture of bleached kraft pulp and CNFs. The persimmon byproduct bleached kraft pulp (PB-BKP) was made at the optimum pulping and bleaching conditions reported in the previous study and the CNFs were made from PB-BKP and commercial hardwood bleached kraft pulp (Hw-BKP) by refining and micro-grinding processes. After micro-grinding, the particle size, viscosity, zeta potential, and fiber width were evaluated according to the pass number of fibrillation. The appearance of the CNF slurries showed no significant difference between PB-BKP and Hw-BKP. It was found that nanoization of PB-BKP and Hw-BKP proceeded sufficiently when the pass number was five or more. In addition, as the pass number increased, the low shear viscosity of CNF increased, the particle size decreased, and no significant change was observed in the zeta potential. Looking at each pulp, CNF made of PB-KBP had higher fiber width and particle size than Hw-BKP in the initial pass number, but the difference decreased when the pass number was nine. Therefore, CNF made with PB-BKP and CNF made with Hw-BKP showed similar characteristics after the sufficient pass number of micro-grinding. Based on the results, we concluded that persimmon tree by-products can be used as raw materials for the production of CNF.

Effects of hemicellulose composition and content on the interaction between cellulose nanofibers

In this study, cellulose nanofibers (CNFs) from softwood and hardwood kraft pulps were prepared with different hemicellulose contents, and the effects of the hemicellulose compositions and contents on the interaction between CNFs were studied. In addition, the effects of CNF interaction on the CNF dispersion stability and viscosity characteristics in the aqueous state were investigated. Using quartz crystal microbalance with dissipation, the results of the interaction analysis revealed that hemicellulose moderated the strength of the interaction between CNFs, and the intensity of the interaction changed according to the hemicellulose compositions. The interaction between galactoglucomannans was stronger than that between glucuronoxylans, and CNFs prepared from softwood pulp containing mainly galactoglucomannan showed stronger interaction between CNFs than those prepared from hardwood pulp containing mainly glucuronoxylan. The presence of hemicelluloses on the surface of CNFs improved the dispersion stability and increased the viscosity. However, the intensity of the interaction between CNFs, which is dependent on the type of hemicellulose, did not affect these properties. The properties of CNFs in the aqueous state are determined by not only the interaction between CNFs but also several factors such as the morphology of CNFs and physical properties of hemicelluloses.

New technology for developing a lightweight refiner plate for hardwood kraft pulp fibers

Sand casting makes it difficult to manufacture a fine bar plate for low intensity refining. This study introduced a novel technology for manufacturing lightweight fine bar plates and compared the effects to traditional bar plates. The lightweight fine bar plate base was manufactured using a lightweight aluminum alloy and stainless-steel. Because the bars were inserted into the plate vertically without the draft angle, the stock throughput was improved by approximately 27% compared to the sand-casted bar plates. Additionally, the lightweight fine bar plate maximized internal and external fibrillation while minimizing fiber length loss. In conclusion, the lightweight fine bar plate was shown to be more effective in improving the strength properties of paper and reducing energy consumption.

Using ionic liquid (EmimAc)-water mixture in selective removal of hemicelluloses from a paper-grade bleached hardwood kraft pulp

In this paper hemicellulose was separated by using 1-ethyl-3-methylimidazolium acetate (EmimAc, an ionic liquid) -water mixtures from a paper grade market bleached hardwood kraft pulp to produce dissolving pulp. Pure EmimAc dissolves pulp fibers completely in 30 min at ambient temperatures. By adding water (as an antisolvent to EmimAc system) the cellulose dissolution decreases and by optimizing the conditions, hemicellulose is largely removed while cellulose remains as the solid residue (dissolving pulp). At optimal conditions: molar ratio of water to EmimAc of 2, 60 °C, an alpha-cellulose content of 92.2%, with a high yield (78 wt%) was obtained. The viscosity of the solvent mixture decreases by increasing water to EmimAc molar ratio, which improves the mobility of ions, thus, facilitating their penetration into pores and lumens of the fibers during the dissolution process. Cellulose purity increases and purified cellulose yield decreases with the increases in temperature and water content (up to 2 wt%) in the mixture. This study implies that the optimal EmimAc/water mixture is an effective system to separate hemicellulose from hemicellulose/cellulose matrix.

Forecasting the Import Price of Hardwood Bleached Kraft Pulp Using a Time-Series Model

Managing the import price risk of hardwood bleached kraft pulp (Hw-BKP) is a major concern of the Korea paper industry due to high price volatility. The primary objective of this study is to develop forecasting models for the import price of Hw-BKP as a tool to reduce price risk. Six different types of extended autoregressive models with various rolling window size were evaluated based on multiple accuracy measures. Results show that forecasts from the models with exogenous and monthly dummy variables are more accurate than the others. An autoregressive model with exogenous and monthly dummy variables model (ARMX) using a window size of 36 months outperforms the other models. When applying the model, it is possible to reduce the mean absolute error (MAE) by 24.6% and the root mean square error (RMSE) by 35.3% compared to a naive forecast model.

The surface softness and mechanical properties of wood pulp–lyocell wet-laid nonwoven fabric

This study explores the tensile properties of wet-laid nonwoven fabric made from softwood bleached kraft pulp (SwBKP), hardwood bleached kraft pulp (HwBKP), dissolving pulp (DP), and Lyocell. Five different ratios of wood pulp and Lyocell (0/100, 10/90, 20/80, 30/70, 40/60, and 50/50) were manufactured using papermaking technology, which is similar to wet-laid technology. The results indicate that the properties of strength and surface softness of a nonwoven fabric are enhanced by the contribution of the entanglements of wood pulp–Lyocell. Of the three pulps, SwBKP is superior to both HwBKP and DP on account of its higher properties of density and tensile strength, which are increased by refining treatments. In terms of the surface softness component results, HwBKP has a lower MMD value than the other samples. The SwBKP–Lyocell mixing ratios with the minimum ratio of 30/70 were found to offer sufficient tensile strength with improved softness.

Transparent, water-stable, cellulose nanofiber-based packaging film with a low oxygen permeability

Herein, we report on a transparent, water-stable, high oxygen barrier packaging film made from a combination of cellulose nanofiber (CNF) and a fluoropolymer (FP) coating. Nanofibrillation of the hardwood kraft pulp was carried out using succinic anhydride pretreatment and aqueous counter collision (ACC) technique to obtain ultrafine (5–7 nm) succinylated cellulose nanofibers (SCNF), which was readily fabricated into a thin coating (on PET film) as well as a self-standing film. Introducing the FP topcoat on SCNF enabled a synergistic enhancement of both oxygen barrier performance and stability against water-swelling.

Structural analysis of CaCO3 nanoparticle/pulp fiber composites by tube flow fractionation

Two slurries that consisted of precipitated calcium carbonate (CaCO3) nanoparticles and unbeaten hardwood bleached kraft pulp (HBKP) were prepared via ultrafine bubble and mixing methods. In the ultrafine bubble method, a CO2 gas flow was bubbled into a HBKP slurry that contained Ca(OH)2 to prepare a precipitated CaCO3/HBKP composite slurry. The HBKP/water and precipitated CaCO3/water slurries were prepared separately and mixed to prepare a precipitated CaCO3/HBKP mixture slurry. Each of the two CaCO3/HBKP slurries was separated into five fractions using a tube flow fractionation (TFF) system. The first and second fractions consisted of long HBKP fibers and fiber aggregates. The third fraction had the highest mass ratio of the components in the five fractions, and it had approximately 1-mm-long HBKP fibers. The fourth fraction contained primarily HBKP short fibers and CaCO3 aggregates. Thus, the CaCO3/HBKP components in the slurry were separated adequately by TFF, depending on their hydrodynamic sizes. The average width of each fraction in the CaCO3/HBKP composite slurry was always larger than that of the corresponding fraction from the CaCO3/HBKP mixture slurry, which indicated that precipitated CaCO3 nanoparticles and their aggregates attached stably to long and short pulp fiber surfaces in the composite slurry.

Enhancement of delignification by ionic liquids pretreatment and modification of hardwood kraft pulp in preparation for bleaching

Ionic liquids (ILs) pretreatment is shown to improve the pulp bleachability and modify the physical strength of the hardwood pulp during the oxygen-chlorine dioxide-hydrogen peroxide (ODP) bleaching. The pretreatment enhanced lignin removal in ODP bleaching, resulting in decreased lignin content of the pretreated pulp. The brightness and strength properties were improved. In particular, the folding strength was increased by 153% relative to the control when the pulp was pretreated by [TEA][HSO4]. The analysis of scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction confirmed the enhancement of delignification in ILs pretreatment by the removal of hemicellulose and lignin on pulp fibers’ surface, and the well-preserved fiber framework of the hardwood pulp fibers during ODP-bleaching.