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Guest Editorial: Coating research addresses new product demands in response to global pandemic, TAPPI Journal November 2020
ABSTRACT: For all of us, the year 2020 has been one of significant challenge. Our communities, companies, institutions, organizations, and families have had to make many tough decisions and change our way of life as a result of the global pandemic.
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Investigation of the influencing factors in odor emission from wet-end white water, TAPPI Journal October 2020
ABSTRACT: Emission of malodorous gases, such as volatile organic compounds (VOCs), hydrogen sulfide (H2S), and ammonia (NH3) during pulping and papermaking has caused certain harm to the air environment and human health. This paper investigated the influencing factors of odor emission from wet-end white water during the production of bobbin paper in a papermaking mill using old corrugated containers (OCC) as raw material. The concentration of malodorous gases emitted from wet-end white water was determined with pump-suction gas detectors. The results indicated that low temperature could limit the release of malodorous gases from white water. Specifically, no total volatile organic compounds (TVOC), H2S, and NH3 was detected at a temperature of 15°C. The concentrations of malodorous gases were slightly increased when temperature increased to 25°C. When temperature was 55°C, the released concentrations of TVOC, H2S, and NH3 were 22.3 mg/m3, 5.91 mg/m3, and 2.78 mg/m3, respectively. Therefore, the content of malodorous gases significantly increased with the temperature increase. The stirring of white water accelerated the release of malodorous gases, and the release rate sped up as the stirring speed increased. However, the total amount of malodorous gases released were basically the same as the static state. Furthermore, the higher the concentration of white water, the greater the amount of malodorous gases released. The pH had little influence on the TVOC release, whereas it significantly affected the release of H2S and NH3. With the increase of pH value, the released amount of H2S and NH3 gradually decreased. When pH reached 9.0, the release amount of H2S and NH3 was almost zero, proving that an alkaline condition inhibits the release of H2S and NH3.
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Editorial: Special coating issue contains highlighted works from TAPPICon 2023, TAPPI Journal November 2023
ABSTRACT: Did you know that TAPPI’s Coating and Graphic Arts Division has changed its name to Coating, Printing, and Surface Enhancement (CPSE) Division? This change occurred mid-year, as our members realized that the new name fits much better with the day-to-day workings of the Division, as well as the broader activities to functionalize and add value to paper and paperboard that continue to expand into new arenas.
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Impact of different calendering strategies on barrier coating pickup, TAPPI Journal November 2023
ABSTRACT: Paper was pre-calendered in a pilot scale configuration with a traditional soft nip calender and a metal belt calender. All calendering strategies reduced surface roughness and permeability of the samples, but different strategies affected the surface roughness and permeability differently. The metal belt calender seemed to have a larger effect on the large-scale variations compared to the soft nip calender. Six test points from the pilot calendered papers were chosen for laboratory coating studies. Uncalendered paper was included as reference samples. The calendered samples and the reference were pre-coated with a regular pigmented coating consisting of a ground calcium carbonate (GCC) pigment and a styrene acrylate (SA) latex. Both uncoated and pre-coated substrates were barrier coated with a polyvinyl alcohol (PVOH) in one and two layers. The coating pickup was determined gravimetrically, and the barrier properties were evaluated with TAPPI Standard Test Method T 454 grease resistance test. All samples needed two PVOH coating layers to form a grease barrier. The uncalendered sheets showed the best results with one coating layer, but this was at the expense of a higher coating pickup compared to the calendered sheets. The barrier coating pickup could be reduced by a combination of high temperature metal belt calendering and pre-coating. The high temperature and long residence time in the nip enabled plasticization of the fibers. This led to an irreversible deformation, even after water application. This meant that the smoothness obtained during calendering would be less affected by water-induced roughening during the coating operation.
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Use of kaolin clay in aqueous barrier coating applications, TAPPI Journal November 2023
ABSTRACT: Paper-based packaging with barrier effect, as opposed to single use plastics, is gaining more prominence for sustainability reasons. At the same time, latex- or biopolymer-based aqueous barrier coating dispersions are increasingly being adopted as a better alternative to the traditional barrier coating materials, such as wax, surface active chemicals, and polyethylene. In this work, studies were performed to determine the influence of different kaolin clays in latex binder-based aqueous coatings on barrier properties, namely, oil and grease, water resistance, and water vapor transmission rate, by applying coatings to solid bleached sulfate (SBS) paperboard substrate in the laboratory. The aim was to explore potential benefits of using kaolin clay to replace some of the latex binder in coating and improve or maintain various types of barrier performance and blocking without negatively influencing the other performance attributes, including heat seal. The delaminated clay with the highest shape factor provided improved barrier properties over the clays of low shape factor. The ultrafine and non-delaminated clays required significantly higher coat weights to reach satisfactory barrier properties. Coatings with different latex levels indicated that a considerably high proportion of coarse delaminated clay can be incorporated to replace latex binder, while still achieving exceptional barrier properties. Furthermore, a change in binder system was found to significantly alter the barrier properties and the role that a mineral pigment can play. The results indicate that a proper selection of binder systems for each barrier property would be required while considering the clay/latex coating systems.
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Kraft pulp viscosity as a predictor of paper strength: Its uses and abuses, TAPPI Journal October 2023
ABSTRACT: For bleached kraft pulps, two factors govern paper strength: the individual fiber strength, and the bond strength that adheres the individual fibers together in the paper matrix. Inherent fiber strength is related to the length of the carbohydrate polymers, also known as the degree of polymerization (DP). Average DP (DP) is inferred by performing pulp viscosity measurements. Under certain circumstances during kraft pulping and bleaching, the average polymer lengths can be shortened, resulting in lower pulp viscosity, and may indicate fiber damage. Fiber damage typically manifests itself as a reduction in tear strength for well-bonded handsheets.This paper will review the literature on how pulp viscosity can predict paper/fiber strength and how it can be used as a diagnostic tool. It can be a means to monitor pulp quality during pulping and bleaching, as well as to alert when such operations approach a critical threshold. However, viscosity losses must be carefully and judiciously analyzed. Like most diagnostic tools, viscosity measurements can be misused and abused, which can lead to incorrect inferences about intrinsic fiber strength. This review will also cover these misuses. The overall goal is to provide the papermaker a better understanding of what pulp viscosity is, how it correlates to potential sheet strength, and what its limitations are. It will be illustrated that when pulp viscosity drops below a critical value, it will indicate an appreciable deterioration in the paper’s tear and tensile strength.
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Next generation dry strength additives: Leveraging on-site synthesis to develop high performance glyoxalated polyacrylamides, TAPPI Journal January 2024
ABSTRACT: Although glyoxalated polyacrylamides (gPAMs) have been described since the 1950s, the freedom to design new materials based on this chemistry has been limited by practical concerns; namely, a balance between solution concentration and material characteristics must be met to make the economics of gPAM strength additives work for the paper industry. For traditional “delivered” gPAMs, only a very narrow range of polyacrylamide molecular weights and compositions could be considered for glyoxalation. However, the development and successful implementation of automated reactor equipment that allows for the synthesis of gPAMs from glyoxal and polyacrylamide copolymers at the mill, known as “on-site” glyoxalation, obviates the shipping and stability concerns that have traditionally held back gPAM development. As such, on-site generators represent a platform that enables the glyoxalation of materials that would otherwise not have been suitable for use in a traditionally delivered gPAM product. These on-site generators therefore open new avenues for polymer design to allow for the creation of the next generation of strength additives. By leveraging the synthetic freedom of the on-site generators, a suite of high performance gPAMs has been designed, yielding materials that provide both exceptional strength and drainage performance in poor quality furnishes.
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Improving monochloramine performance with innovative sensor-controlled dosing, TAPPI Journal January 2024
ABSTRACT: Monochloramine (MCA) has become one of the major oxidant chemistries for biological control in the paper industry. Feedback control, such as oxidative-reductive potential (ORP), is often used to provide better control of a dosing scheme. The trademarked Ackumen MCA-i is a chemical-digital solution that uses artificial intelligence with actionable insights to stabilize the wet-end process, providing improved performance and reduction in overall chemical costs. Accurate sensor-controlled dosing can be tied to multiple inputs, such as production rates, grade changes, pH, ORP, chlorine residual, freshwater usage, and more. In this study, a case history will be presented to demonstrate how this technology provided a more consistent MCA molecule throughout the process, resulting in a higher level of efficacy and reduction in chemical costs.
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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.