Nordic Pulp & Paper Research Journal

Journal Information
ISSN / EISSN : 0283-2631 / 2000-0669
Published by: Walter de Gruyter GmbH (10.1515)
Total articles ≅ 2,255
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Tai Ju Lee, Hyoung Jin Kim
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0053

Abstract:
Regulation of hexavalent chromium is based on Waste Framework Directive 1994/62/EC, European Commission and publication of the World Health Organization. Herein, detection of hexavalent chromium was performed by alkaline digestion and instrumental analysis which was demonstrated in USEPA methods. However, UV-vis detection method could be affected by some metal ions reacted with diphenylcarbizide. Actually, various interfering elements, such as Ni, Fe, Al, and Cu, were detected and selected by ED-XRF in paper materials. In order to improve accuracy of analysis results of hexavalent chromium in paper materials based on USEPA methods, the interfering elements was removed by liquid–liquid extraction with carbonate media using tricaprylmethylammonium chloride and chloroform after alkaline digestion. Consequently, the temperature for alkaline digestion was between 85 and 95 °C. Hydrochloric acid was proper complex tricaprylmethylammonium-Cr(VI) in the procedure of liquid extraction. After that hexavalent chromium was completely extracted using of 1 M sodium hydroxide solution. The technique for analyzing the hexavalent chromium used in liquid–liquid extraction significantly reduced the errors caused by the interfering elements, Fe and Cu. Thus, application of the extraction method was efficient in removing the interfering elements, which increased the recovery ratio of the hexavalent chromium from paper materials by 90 %.
, Christer Sandberg, Anders Karlström, Göran Thungström, Per Engstrand
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0011

Abstract:
In this study, the effect of process- and online analyser configuration on pulp quality control is explored. The following parameters were included: analyser sampling interval, time delay, measurement error magnitude, and latency chest residence time. Using different values of parameters in a process model, a range of configurations were constructed. For each configuration, the achievable control performance was evaluated using an optimization approach. PI controller settings were chosen based on minimization of the integrated absolute error (IAE) in pulp quality after an input step disturbance. The results show that reducing the sampling interval improves performance also when the interval is smaller than the chest residence time or the analyser delay. Moreover, reducing the chest residence time can reduce the IAE by up to 40 %. However, reducing the residence time to lower than 1/3 of the sampling interval does not improve performance. Further improvement is possible if the analyser delay is reduced. The compromise between reducing the IAE and avoiding creating variation by acting on measurement error has a strong influence on the results. In conclusion, pulp quality control performance can be improved significantly by making changes to the studied configuration parameters.
, Maria Boman, Olena Sevastyanova, Mikael E. Lindström, Juha Fiskari
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0022

Abstract:
Bleachability is evaluated as how easily a pulp sample is bleached and it depends on the structure of residual lignin and carbohydrates. Also, the bleachability varies depending on the bleaching sequence. ECF light sequences have been improved significantly in the recent years. However, we still don’t fully understand how ECF light bleach plants are optimally run. This work studies the bleachability of softwood kraft pulp in an ECF light bleaching sequence, (OO)Q(OP)D(PO). Three pulp samples with brown stock kappa number 27, 32 and 35 were bleached and studied for residual lignin, hexenuronic acid and carbohydrate content. It was found that in the bleaching stages that are highly delignifying, it is beneficial with a higher kappa number for the delignifying bleachability. However, in the bleaching stages where the objective is brightness increase, the brightness gain bleachability is improved by a lower kappa number. We also intended to determine which of the three samples had the best suited kappa number for this particular bleaching sequence. According to our results, the bleaching was most effective with kappa number around 32. Although an even higher kappa number resulted in higher yield after cooking, it seemed that this bleaching sequence cannot preserve the yield gain.
Magdolna Pál, , Koltai László, Diana Gregor-Svetec, , Živko Pavlović, Neda Milić-Keresteš
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0041

Abstract:
In this paper, white pixel percentage (WPP) value, as an overall measure of fold crack damages, has been analysed with respect to selected parameters of sample preparation and digitalization process, as well as the results of residual tensile strength. The WPP values were derived by an automated image processing algorithm, developed earlier, based on extensive comparative analysis of the existing computer-aided methods. Results indicate that WPP values correlate well with the extent of fold cracks on the coated samples, as far as the used parameters of sample preparation and digitalization are concerned. In the case of correlation with residual tensile strength, results for samples folded in cross direction revealed that the extent of the visually registered fold cracks agree well with the actual damage, while for samples folded in machine direction, the overall strength losses weren’t alarming, although the fold cracks were detected correctly. In addition, results pointed out that the simplest sample placement position (inner angle of 180°) is not applicable for realistic sample representation. Furthermore, scanners could provide a superior image quality in lab conditions, but for industry application, a camera-based solution would be more purposeful, while micrographs are more suitable for traditional visual analysis.
Hui Zhao, Wenjuan Tao, Haoming Gu, Lifang Guo, Mai Han, Huamin Zhai,
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0049

Abstract:
The mechanical pulp of mulberry branches was evaluated as a raw material for the production of cellulose II and its subsequent conversion to nanocellulose via high-pressure homogenization, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidation, and sulfuric acid hydrolysis. The morphology, chemical structure, crystallinity, and thermal stability of the nanocellulose samples prepared by each method were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, and thermogravimetric analysis. The results showed that nanocellulose prepared by high-pressure homogenization exhibited higher aspect ratio (>100), and the weight loss peak in the DTG chart was 361 °C, with the best thermal stability, whereas that prepared by sulfuric acid hydrolysis featured shorter fiber length (96±31 nm) and a higher crystallinity (78.2 %).The TEMPO oxidized nanocellulose (TOCN) had smaller width (5.5±1.6 nm) and high carboxyl content (1.5 mmol/g). In addition, we have further studied the application of TOCN in the wet end of papermaking, replacing the colloidal SiO2 in CPAM/ colloidal SiO2/APAM retention system with the same amount (3600 ppm) of TOCN. The study found that the strength of the paper obtained by adding TOCN instead of the traditional wet end additives is similar, and the water drainage and retention properties of the pulp are improved.
R. J. Kerekes,
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0044

Abstract:
Refiners develop pulp properties by applying forces on fibres during bar crossings. The size of these forces is critical in developing fibre properties while avoiding fibre shortening. This study has shown that bar force calculated from Specific Edge load (SEL) gives the same result as vector-based derivations of average bar force. Predicted forces agree reasonably well with ones measured by a novel piezo-electric sensor in refiner bars and forces estimated from measurements of fibre shortening.
Shuangshuang Chen, Lirong Lei, Youming Li
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0030

Abstract:
Paper mill effluent has been characterized as recalcitrant because of containing lignin and its derivatives. Since biofilm system exhibits a notable potential for the removal of recalcitrant contaminants, a sequencing batch biofilm reactor (SBBR) was employed to treat coagulated recycled paper mill effluent in this study. The results indicated that the SBBR removed 91.3 % of chemical oxygen demand (COD), whilst total suspended solid (TSS) and color removal reached 83.1 % and 71.0 %, respectively. The microbial analysis suggested that three typical heterotrophic phyla, Proteobacteria, Bacteroidetes and Acidobacteria are dominant bacteria and reflected the removal of recalcitrant contaminants. The COD removal rate of SBBR is evidently superior to conventional activated sludge process due to high sludge concentration as well as long sludge retention time (SRT). Whilst the problem of sludge bulking can be successfully avoided, the blockage of reactor caused by TSS accumulation and microbial growth deserve further investigation.
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0047

Abstract:
Paper is an environmentally friendly, recyclable material whose main material is cellulose, which can be obtained from all kinds of trees and plants, used as writing, printing and packaging material. Due to its structural properties, papers are not resistant to temperature and humidity, as well as problems with ink transfer with its porous structure and experienced negative printability properties. In recent years, especially the growth of the packaging industry has increased the demand for papers with improved printability properties. In order to obtain better printability properties from papers, some processes can be performed in paper production, as well as some surface treatments after production. These processes are paper coating, sizing and calendering. Paper coatings are generally water-dispersed coating solutions with one or more pigments, binders and certain additives to improve the desired properties. With these processes, by filling the gaps between the pores of the paper, a shapely and smooth surface is obtained and good printability is obtained together with the optical and physical properties of the papers. In this study, the interactions and printability properties of different types of pigments with xanthan gum binder were investigated by preparing paper coating formulations using calcium carbonate, barite and talc pigments and xanthan gum as binder. As a result, xanthan is a good coating binder and CaCO 3 {\mathrm{CaCO}_{3}} from the compared pigments is the most suitable compared to the other 2 pigments, considering all the studied areas.
, Barry Hirtz, Carl Sheehan, Travis Reinheimer, Philip Loewen, Bhushan Gopaluni
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0048

Abstract:
Rotary kilns are large-scale unit operations that are critical to many industrial processes such as cement production, pyrometallurgy, and kraft pulping. As expensive, energy-intensive units, it is imperative from both an economic and environmental perspective to ensure efficient operation of the rotary kiln. To provide additional insights for operation and maintenance, rotary kilns are increasingly outfitted with more advanced sensing technology. Leveraging this supplementary data requires strategies and active efforts towards storage, processing, and visualization. In this work we provide a visualization strategy for industrial thermal camera data that is measured along the shell profile of a rotary lime kiln. The proposed strategy assists specifically with the visualization of ring formation at different timescales, but it also serves more generally as a useful tool for operations management. This paper describes the visualization strategy, provides a demonstration with industrial data, and offers open-source resources for interested users to implement it themselves.
Hongfeng Zhang, Ester Tsenter, Paul Bicho, Erin A. S. Doherty, Richard Riehle, Jose Moran-Mirabal,
Nordic Pulp & Paper Research Journal; https://doi.org/10.1515/npprj-2021-0005

Abstract:
Seven copolymers of maleic anhydride were hydrolyzed and impregnated into sheets of bleached softwood kraft pulps to enhance market pulp properties. Drying the impregnated pulps at 120 °C for 10 minutes, attached to the fiber surfaces up 0.16 meq of carboxyl groups per gram of dry pulp. Heating the impregnated pulps regenerates succinic anhydride moieties which can then form stable ester linkages with cellulosic hydroxyls. The pH of the impregnation solution is important. Impregnation with solutions at pH 8 gave polymer contents without repulping issues. By contrast, impregnation at pH 4 gave dried pulp sheets that were too strong to enable repulping in a paper mill. Although most of the seven copolymers were fixed to cellulose, poly(ethylene-alt-maleic anhydride) gave the highest density of carboxyl groups. The simplicity of waterborne polymers and mild drying temperatures suggests maleic anhydride copolymer treatment could be implemented in a conventional market pulp mill.
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