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Setting priorities in CNF particle size measurement: What is needed vs. what is feasible, TAPPI Journal February 2023
ABSTRACT: Measuring the size of cellulose nanomaterials can be challenging, especially in the case of branched and entangled cellulose nanofibrils (CNFs). The International Organization for Standardization, Technical Committee 6, Task Group 1—Cellulosic Nanomaterials, is exploring opportunities to develop standard methods for the measurement of CNF particle size and particle size distribution. This paper presents a summary of the available measuring techniques, responses from a survey on the measurement needs of CNF companies and researchers, and outcomes from an international workshop on cellulose nanofibril measurement and standardization. Standardization needs differed among groups, with Japanese companies mostly requiring measurements for product specification and production control, and other companies mostly needing measurements for safety/regulatory purposes and for grade definitions in patents. Among all the companies, average length and width with percen-tiles (D(10), D(50), D(90)) were the most desired measurands. Workshop participants concurred that defining the location(s) on the CNF at which to measure the width and the length is an urgent and complex question. They also agreed that methods are needed for rapid particle size measurement at the nanoscale. Our recommendation within ISO is to start work to revise the definition of CNFs and develop sample preparation and measurement guidelines. It was also recommended that further research be done to reproducibly prepare hierarchical branched CNF structures and characterize them, develop automated image analysis for hierarchical branched CNF structures, and develop a classification system encompassing measurements at multiple size ranges from micro- to nanoscale to fully characterize and distinguish CNF samples.
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A discrete element method to model coating layer mechanical properties with bimodal and pseudo-full particle size distributions, TAPPI Journal July 2023
ABSTRACT: The mechanical properties of paper coating layers are important in converting operations such as calendering, printing, and folding. While several experimental and theoretical studies have advanced our knowledge of these systems, a particle level understanding of issues like crack-at-the-fold are lacking.A discrete element method (DEM) model is used to describe bending and tension deformations of a coating layer. The particles in the model are either bimodal distributions or pseudo-full particle size distributions of spherical particles. The impact of particle size distribution on the predicted mechanical properties of the coating layer is reported. Inputs to the model include properties of the binder film and the binder concentration. The model predicts crack formation as a function of these parameters and also calculates the modulus, the maximum stress, and the strain-to-failure. The simulation results are compared to previous experimental results. Reasonable predictions were obtained for both tensile and bending for a range of latex-starch ratios and at various binder concentrations. The influence of particle packing density on mechanical properties is reported.
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Editorial: The state of cellulosic nanotechnology: June conference captures current and emerging trends, TAPPI Journal July 2023
ABSTRACT: From June 12-16, 253 participants from 18 countries gathered in Vancouver, BC, Canada, for TAPPI’s 2023 International Conference on Nanotechnology for Renewable Materials. Representatives from academia, industry, and federal research institutes could choose from among 140 technical presentations on production, characterization, applications, and functionalization of renewable nanomaterials.
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Effect of fly ash-based calcium silicate on physical properties of cardboard paper, TAPPI Journal July 2023
ABSTRACT: This work reported the possibility of using fly ash-based calcium silicate (FACS) as filler for papermaking and waste fiber to synthesize cardboard paper. The adverse effects of FACS filler on paper strength were improved by using cationic starch modification, surface size, and interlayer-filled technology. Physical property tests indicated that the increase of filler content leads to a decrease in paper strength and an increase in bulk, but at the same content, the strength properties of paper modified by cationic starch were significantly improved, and the absorption resistance was lower. The paper had better absorption resistance than the original FACS paper after surface size. In addition, the absorption resistance and strength of the interlayer filling paper were better than the original FACS-filled paper, and the absorption resistance was the best. The results support the potential use of FACS as a low-cost filler for cardboard paper production.
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Experimental study and prediction of two-phase flow pattern distribution diagrams in multi-channel cylinder dryer, TAPPI Journal July 2023
ABSTRACT: The multi-channel cylinder dryer (MCD) is designed to improve heat transfer. Although there are numerous research studies on the pressure drop, heat transfer characteristics, and flow pattern in static state of MCD, there is little research on the flow pattern in the rotating state. In this paper, the distribution of flow pattern in MCD under different rotating speeds and steam mass flow rates is studied. Furthermore, the logistic regression method (LR) is used to predict the flow pattern diagrams. The results show that in the front section of the flow channel, the flow pattern is basically annular flow, which is not affected by mass flow rate and rotating speed. On the other hand, wavy flow, vortex flow, slug flow, and bubble flow can be observed when the fluid enters the middle and the end section. The higher the rotating speed and the steam mass flow rate, the more the flow pattern tends to be an annular and wavy flow. At the end of the passage, the flow pattern is mainly slug flow. The predicted flow pattern diagrams are in good agreement with the experimental result, and to obtain an effective flow pattern in the middle and the end section of the flow channel, the influence of increasing rotating speed is greater than that of increasing steam mass flow rate. However, the specific rotating speed, steam mass flow rate, and other parameters should still be set by combining with the actual situation. This work can provide some references for the further study of MCD flow characteristics.
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Evaluating the effect of recovery boiler operation on green liquor dregs concentration using multivariate analysis, TAPPI Journal June 2023
ABSTRACT: Poor settling and filterability of green liquor dregs has been a persistent problem in many kraft pulp mills. While the concentration and settling/filtering behaviors of dregs are expected to be related to how black liquor is burned in recovery boilers, the effect of boiler operation is not well understood. A systematic study was conducted to examine how recovery boiler operation may affect the dregs concentration in the raw green liquor (RGL) at three kraft pulp mills using SIMCA, a multivariate data analysis (MVDA) program. Daily average boiler operating data from three kraft mills were analyzed over a 3-year period. Results of both principal component analysis (PCA) and partial least squares regression (PLS) suggest that the main boiler operations contributing to high dregs concentrations in RGL are low liquor firing load, low bed temperature, poor char burning, and unstable char bed.
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External fibrillation of wood pulp, TAPPI Journal June 2023
ABSTRACT: Pulp refining produces external fibrillation consisting of fibrils tethered to fiber surfaces, in addition to loose fibrils and fines. Both contribute to a larger bonding area that increases paper strength, but tethered fibrils have less likelihood of being washed out during papermaking. This study postulates the mechanism by which refining produces external fibrillation and the optimum conditions for doing so.The postulated mechanism is surface abrasion during sliding of fibers in refiner gaps. External fibrillation occurs when forces are great enough to partially dislodge fibrils from fiber surfaces, but not large enough to break the fibrils. The refining intensities to achieve these forces were determined by a mathematical model and experiments using a laboratory disc refiner. The optimum intensities in terms of specific edge load (SEL) for chemical pulps were about 0.1 J/m for hardwoods and 1.0 J/m for softwoods. An extension of this study suggested that abrasion may also account for most of the energy consumed in the mechanical pulping process.
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Water chemistry challenges in pulping and papermaking • fundamentals and practical insights: Part 2: Conductivity, charge, and hardness, TAPPI Journal June 2023
ABSTRACT: Although water is essential to the papermaking process, papermakers often overlook its importance and focus on fibers, fillers, and chemical additives. A better understanding of water properties and chemical interactions associated with water at the wet end leads to a sound foundation for high-quality paper production and smooth operation. Water is an excellent solvent for ionic substances, both organic and inorganic. These substances contribute to system conductivity, charge, and hardness and significantly impact the papermaking process. Part 1 of this paper, published in TAPPI J. 21(6): 313(2022), discussed fundamental water properties, water chemistry, and the impact of pH on pulping and papermaking operations. In this paper, we review definitions, sources, and the typical symptoms of the effect of conductivity, charge, and hardness on the productivity of the papermaking process. Sources of conductivity, charge, and hardness impacting these factors, measurement methods, and available correction strategies for their control are also discussed.
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Value creation by converting pulp mill flue gas streams to green fuels, TAPPI Journal March 2023
ABSTRACT: Climate change mitigation induces strong growth in renewable electricity production, partly driven by shifts in environmental policies and regulation. Intermittent renewable electricity requires supporting systems in the form of sustainable hydrocarbon chemicals such as transportation fuels. Bulk chemical production fits well into a pulp mill environment, given their large volumes, stable operation, and ample supply of biomass-based carbon feed-stock in the form of flue gases. Until now, the utilization of the flue gases from conventional operation of a pulp mill has received little attention. Harnessing these flue gases into usable products could offer additional value to mill operators, while also diversifying their product portfolio. However, electricity-based fuels and products require extra energy in the conversion step and may not be commercially competitive with current fossil products under the current regulation. There might also be uncertainties about future commodity prices. Thus, the objective of this study is to estimate the economic competitiveness and the added value of selected side products that could be produced alongside conventional pulp and paper products. A typical modern pulp mill is modeled in different product configurations and operational environments, which allows testing of various development paths. This illustrates how the overall energy and mass balance of a pulp mill would react to changes in different final products and other parameters. The focus of the study is in synthetic methanol, which is produced from flue gases and excess resources from the mill, with minimal interference to the pulping process. The results aid in assessing the necessity and magnitude of a premium payment for subsidizing green alter-natives to replace current fossil fuels and chemicals. Additionally, the results function as an indicator of the development state of the pulp and paper industry in the turmoil of climate change regulation. The results indicate that power-to-X systems offer one more viable pathway alternative for broadening the product portfolio of the pulp and paper sector, as well as opening new flexibility measures and services to grid stabilization. Market conditions were found to have a significant impact on the perceived profitability.
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Quantification of the degree of preference for different tissue products based on a hand-felt tissue test panel, TAPPI Journal May 2023
ABSTRACT: In this study, we successfully established a quantification model to determine the preference (PF) for different tissue products based on the results of a hand-felt tissue testing panel. The panel ascertained that products designed with four-ply tissues provided higher total tensile strength (TTS) and hand-felt surface softness (HSS) than did those of the three-ply, two-ply, and single-ply products.When practically tested with a tissue softness analyzer (TSA), the four-ply tissue product had a softness (TSA-HF) advantage; however, in human panel tests, more than half of the participants could not be sure of the hand-felt bulk softness (HBS) of the four-ply tissue product. This was mainly because when using the four-ply tissue, the hand-held test pad gave an overall perception distinctly different from those of the hand-held two- or three-ply products, which also differed from the flattened state of test pieces used in the instrumental softness tests. Users could distinctly feel that a product was safer (better TTS) and more comfortable (higher hand-held surface softness). Thus, the four-ply tissue product was accorded a higher preference.