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Z-direction chemical analysis for new application methods, TAPPI Journal January 2023
ABSTRACT: In conventional wet-end chemical addition during paper production, chemical distribution through the z-direction of the sheet is usually not considered an important characteristic. With a nontraditional chemical dosing approach, such as foam-assisted additive addition, the chemistry can appear at different concentrations throughout the sheet, typically in a z-direction gradient. To fully understand the strength properties of the sheet, it is helpful to view or quantify the chemical distribution through the sheet in the z-direction. One qualitative method uses a dye technique along with confocal laser scanning microscopy to generate an image where the relative chemical concentration can be observed. A quantitative method involves compiling nitrogen analyses of layered subsections of the sheet into a composite graph of relative chemical concentration vs. the z-direction of the sheet. Chemical distribution analysis can be paired with traditional z-direction strength tests, such as Scott bond and z-direction tensile, to help one understand and improve the chemical addition process and its effects.
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Pareto-based design of experiments for identifying and comparing optimum sealing parameters of heat sealing applications in packaging machines, TAPPI Journal June 2023
ABSTRACT: Sealing is one of the most important process steps in industrial packaging, because the sealed seam is the most sensitive section of a package in terms of quality. For this reason, a major focus in flexible packaging is the sealing process, and among this, heat sealing is the most frequently used technology. In detail, applications of heat sealing processes are confronted with four conflicting objectives: increasing seam quality, reducing dwell time, reducing sealing temperature, and increasing process robustness towards varying conditions. Typical problems, such as identification of the optimum process parameters or selection of the most appropriate packaging film, are subject to these conflicting objectives.This paper presents a recently published design of experiments for characterizing and comparing heat sealing properties of packaging films based on a multi-objective optimization algorithm. The approach provides easy-to-read charts showing all optimum sealing parameters with regard to the four essential objectives of heat sealing: seam quality, dwell time, sealing temperature, and process robustness. Three case studies show exemplary applications of the new approach: 1) analyzing transport damages of beverage powder packages; 2) identifying and comparing optimum sealing parameter of a standard, mono-material, and fiber based packaging film regarding tightness and visual properties of the produced sachets; and 3) analyzing the effect of additional aluminum layers on sealing characteristics regarding hot-tack.The new design of experiments may provide the basis of a standard test method for the identification of optimal sealing parameters in the heat sealing processes.
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Editorial: New coating grades require new tests: Barrier performance inside the package, TAPPI Journal November 2024
The TAPPI Journal special Coating issue is an annual issue that focuses on paper coating and coated papers. It is drawn from presentations at TAPPICon and from other submissions on the topic of paper coating. The TAPPICon 2024 Coating track was rich in high-quality technical content. In fact, the papers were of such significance that Coating members of the TAPPI Journal Editorial Board, which include me, Gregg Reed, and Gregory Welsch, decided that a second paper coating-related special issue would be appropriate for the TAPPI Journal editorial calendar. In addition to the current issue on Barrier Coating Testing, there will be another issue on Coating Fundamentals in early 2025.
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Quantification of block testing for coated paper substrates, TAPPI Journal November 2024
ABSTRACT: Block resistance is a critical property for coated paper and board substrate that will be rolled, stacked, or otherwise contact itself after coating. Small differences in the coated substrate’s blocking can determine whether the substrate can be successfully used for its designated purpose. However, this crucial property is typically evaluated using a qualitative scale that is based on subjective operator ratings and impacted by factors that include: (1) sound of coated substrate during separation, and (2) force with which substrates are separated. This paper tests the hypothesis that quantifying the block test by measuring the force required to peel samples apart improves the test by: (1) providing more standardized testing conditions by controlling peel force and rate; (2) more clearly differentiating samples that experience minimal to some blocking; and (3) maintaining customizability to evaluate customer-specific test conditions. The method developed in this study uses a standard block tester and block testing conditions, but it peels the coated paper samples using a hot tack/heat seal instrument with force measurement capabilities. This paper demonstrates, using the instrument’s heat seal capabilities, that it can measure peel forces that represent the full range of observable block scores. The efficacy of this method was evaluated by having a group of trained operators engage in a randomized, blind experiment where they assessed block resistance on a set of coated paper samples using a modified qualitative block scale and compared their results to force measurements collected using the proposed method. The sample set included two coatings that have successfully run in commercial trials with minimal blocking, and one coating that experienced significant blocking in commercial trials despite only exhibiting some blocking at standard block test conditions in laboratory testing. The quantitative test method presented in this paper clearly differentiated these samples, whereas the qualitative assessment could not predict which samples had suitable block resistance for commercial use. As any tensile tester capable of measuring with 0.1 N resolution can be used for the Quantitative Block Test, the proposed method can be widely adopted. Furthermore, this method can be used for any block condition.
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Evaluation of folding effects on coating damage, TAPPI Journal November 2024
ABSTRACT: Barrier coatings on paperboard need to maintain integrity during converting and end-use for effective barrier performance. Folding is one of the most common deformations during converting; however, factors that affect damage during folding are not well defined. This is partly because methods to fold specimens and characterize damage are not standardized and the results are generally not transferable. In this work, we describe a method to fold paper specimens precisely and reproducibly. The keys to folding include using a defined geometry and controlled deformation. Multiple methods can be used to quantify damage; in this case, we use differences in permeability as a measure of how the coating becomes more open. Damage is sensitive to the degree of compression after the initial folding. Using a shim for support provides a defined amount of compression and minimizes the sensitivity to the applied pressure.
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Colloid chemical aspects of paper formation in the presence of nanofibrillated cellulose and cationic starch, TAPPI Journal September 2024
ABSTRACT: A series of experimental tests were carried out to examine colloidal-scale consequences of optionally treating nanofibrillated cellulose (NFC) with cationic starches of different charge density and dosage (0.5% or 2.0% by weight), adding that material to a furnish prepared from 100% recycled copy paper, and then subjecting the mixture to very different levels of hydrodynamic shear. Tests included optical microscopy, sediment volume tests, sediment velocity tests, and “percent fines” assessment by means of a fiber quality analyzer (FQA). In addition, the zeta potential and charge demand of the studied materials were evaluated. Optical imaging revealed that cationic starch treatment of the NFC tended to agglomerate it into multiparticle clusters, which sometimes could be mostly redispersed by hydrodynamic shear. Subsequent addition of the starch-treated NFC to the default furnish resulted in much of the colloidal material becoming attached to fibers. Subsequent shearing of the mixtures was at least partly effective in separating the clusters of NFC from the fiber surface, resulting in essentially a two-component mixture. Multiparticle NFC clusters coexisted with the fiber suspension, sometimes attached and sometimes not, depending on the details of treatments. Sediment volume tests showed that systems containing cationic starch-treated NFC tended to have a higher density after settling in comparison to untreated NFC; these findings are consistent with the cationic starch acting as a stabilizer on the solid surfaces, allowing them to slide past each other during the settling process. Application of intense hydrodynamic shear tended to result in denser sediment. Results of tests with the sediment velocity messurement and the FQA percent fines assessment did not correlate well with changes in test conditions considered in this study.
Journal articles
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Numerical investigation of the effect of ultrasound on paper drying, TAPPI Journal March 2022
ABSTRACT: The paper drying process is very energy inefficient. More than two-thirds of the total energy used in a paper machine is for drying paper. Novel drying technologies, such as ultrasound (US) drying, can be assessed numerically for developing next-generation drying technologies for the paper industry. This work numerically illustrates the impact on drying process energy efficiency of US transducers installed on a two-tiered dryer section of a paper machine. Piezoelectric transducers generate ultrasound waves, and liquid water mist can be ejected from the porous media. The drying rate of handsheet paper in the presence of direct-contact US is measured experimentally, and the resultant correlation is included in the theoretical model. The drying section of a paper machine is simulated by a theoretical drying model. In the model, three scenarios are considered. In the first scenario, the US modules are positioned in the dryer pockets, while in the second scenario, they are placed upstream of the drying section right after the press section. The third case is the combination of the first and second scenarios. The average moisture content and temperature during drying, enhancement of total mass flux leaving the paper by the US mechanism, total energy consumption, and thermal effect of heated US transducers are analyzed for all cases. Results show that the application of the US can decrease the total number of dryer drums for drying paper. This numerical study is based on the US correlation obtained with the US transducer direct-contact with the paper sample. Thus, future work should include US correlation based on a non-contact US transducer.
Journal articles
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Predicting strength characteristics of paper in real time using process parameters, TAPPI Journal March 2022
ABSTRACT: Online paper strength testing methods are currently unavailable, and papermakers have to wait for manufacture of a complete reel to assess quality. The current methodology is to test a very small sample of data (less than 0.005%) of the reel to confirm that the paper meets the specifications. This paper attempts to predict paper properties on a running paper machine so that papermakers can see the test values predicted in real time while changing various process parameters. This study was conducted at a recycled containerboard mill in Chicago using the multivariate analysis method. The program provided by Braincube was used to identify all parameters that affect strength characteristics. Nearly 1600 parameters were analyzed using a regression model to identify the major parameters that can help to predict sheet strength characteristics. The coefficients from the regression model were used with real-time data to predict sheet strength characteristics. Comparing the prediction with test results showed good correlation (95% in some cases). The process parameters identified related well to the papermaking process, thereby validating the model. If this method is used, it may be possible to predict various elastic moduli (E11, E12, E22, etc.) in the future as the next step, rather than the traditional single number “strength” tests used in the containerboard industry, such as ring crush test (RCT), corrugating medium test (CMT), and short-span compression strength test.
Journal articles
Magazine articles
The Shendye-Fleming OBA Index for paper and paperboard, TAPPI Journal March 2022
ABSTRACT: We are proposing a new one-dimensional scale to calculate the effects of optical brightening agents (OBA) on the bluish appearance of paper. This index is separate from brightness and whiteness indices.In the paper industry, one-dimensional scales are widely used for determining optical properties of paper and paperboard. Whiteness, tint, brightness, yellowness, and opacity are the most common optical properties of paper and paperboard. Most of the papers have a blue cast generated by addition of OBA or blue dyes. This blue cast is given because of the human perception that bluer is whiter, up to a certain limit. To quantify this effect, it is necessary to determine how much blue cast paper and paperboard have. As the printing industry follows the ISO 3664 Standard for viewing, which has a D50 light source, this also plays a very important role in showing a blue cast. Color perception is based on light source and light reflected from an object. The ultraviolet (UV) component in D50 interacts with OBA to provide a reflection in the blue region of the visible spectrum. Use of a UV blocking filter results in measurements without the effect of emission in the blue region. This difference is used in determining the OBA effect in the visible range of the paper. This equation is known as the Shendye-Fleming OBA Index.
Journal articles
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Considerations in managing wastewater odor at pulp and paper operations, TAPPI Journal March 2022
ABSTRACT: Many pulp and paper mills are, at least periodically, faced with the release of odors that can migrate offsite and be considered a nuisance by nearby residents. At chemical pulp mills, perceptible odors associated with reduced sulfur compounds (RSCs) are common, many of which are highly perceptible owing to their low odor thresholds. As releases of RSCs and other odorous substances from production processes are progressively controlled, the proportional contribution from wastewater treatment systems to areal odors can increase. This review paper summarizes important fundamentals of odor generation, source identification, and control. Common odorous substances are identified, and mechanisms for their generation are summarized. Approaches for measuring odorous substances are detailed to enable more effective management, and various odor control strategies are discussed.