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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.
Journal articles
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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.
Journal articles
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Editorial: The innovation engine and the forest products industry value chain, TAPPI Journal October 2023
ABSTRACT: The forest products industry (FPI • pulp, paper, paperboard, building products, allied products, and byproducts) has been continuously innovating as it manufactures and delivers value-added products to consumers worldwide. Integrated pulp and paper mills produce pulp, paper, paperboard, and byproducts like turpentine, tall oil, methanol, lignin, and other chemicals.
Journal articles
Magazine articles
Pulp and paper mills: The original biorefineries — past performance and limitations to future opportunities, TAPPI Journal October 2023
ABSTRACT: Pulp mills have been biorefineries since the invention of the Tomlinson recovery boiler. Unfortunately, the paper industry has done a poor job explaining that concept to the general public. A number of bioproducts in everyday use have been produced by pulp mills for several decades, and new products are routinely being developed. Modern research efforts over the last couple of decades have focused on producing even more products from pulp and paper mills through capacity enhancement and the development of value-added products and liquid transportation fuels to enhance paper mill profitability. Some of these efforts, often referred to as modern biorefineries, have focused so heavily on product development that they have ignored operating and process realities that limit the transformation of pulp and paper mills from the current limited number of bioproducts produced today to economic scale production of these value-added products. In this paper, several of these limitations are addressed. In addition, there are several supply chain, marketing, product quality, and economic realities limiting the value potential for these wholesale conversions of pulp mills into multiproduct modern biorefineries. Finally, the conservative nature and capital intensity of the pulp and paper industries provide a difficult hurdle for conversion to the modern biorefinery concept. These issues are also reviewed.
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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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Editorial: The next phase of research in academia and industry, TAPPI Journal September 2023
ABSTRACT: The pulp, paper, and textile sectors have contrib-uted to lifestyle improvements for people with the development and commercialization of products like toilet tissue, facial wipes, diapers, and feminine hygiene products, to name a few. Research and development (R&D) efforts in these sectors are critical now more than ever due to the need for healthcare and lifesaving products, as became evident with the COVID-19 pandemic. Additionally, the need to meet net-zero carbon goals and the necessity to revive manufacturing in devel-oped economies clearly emphasize the requirement to ex-amine the R&D landscape. Academia, industry, and governments have respective roles to play in this field.
Journal articles
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Filtration efficiency and breathability of selected face masks, TAPPI Journal September 2023
ABSTRACT: Face masks have been used as physical barriers to stop respiratory infections for many years. Due to insufficient and low supply of certified masks, alternative face covers such as face shields, neck gaiters, and fabric reusable masks gained attention during the COVID-19 pandemic. However, for these alternate face masks to fulfill their intended function, they must be effective. Additionally, the level of breathability provided by the makeshift masks must be at a certain level. The work reported in this paper was carried out to determine the relationship between filtration efficiency (FE), breathability, and important physical characteristics of mask substrates. The fiber diameter of the core filter layer was determined using a scanning electron microscope. Five types of face masks (two types of N95, two types of surgical masks, and a 100% knitted cotton fabric) were tested for their FE and breathability using moisture vapor transmission rate (MVTR). The cotton knitted mask had the lowest FE (5.10%•26.47%), while the National Institute for Occupational Safety and Health (NIOSH)-certified N95 mask had the highest FE values (92.10%•99.65%). However, the cotton mask outperformed the N95 in terms of the pressure drop, meaning higher comfort. In general, the N95 face mask provided the best protection against aerosolized particles. According to the regression analysis, the fiber diameter of the mask filter substrate serves as an important predictor of FE of mask substrates. In this study, it was confirmed that fiber diameter is inversely related to the filtration ability. Results show that compact structure with finer fibers will enable higher filtration efficiency. The study lends itself to developing layered face masks to obtain optimum filters with good filtration, better fit, and acceptable comfort for the wearer.
Journal articles
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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.
Journal articles
Magazine articles
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.
Journal articles
Magazine articles
Test method and coating composition impact on measured moisture vapor transmission rate for waterborne coatings on paper, TAPPI Journal November 2024
ABSTRACT: Moisture vapor barrier is one of the necessary performance attributes for paper packages. Two methods are typically employed to assess the moisture vapor transmission rate (MVTR): the gravimetric cup method (ASTM E96) and the MOCON method (ASTM F1249). While those tests have been compared for free standing polymeric films, less is understood about their application in coated paper. Our results show that, despite a general agreement between the two methods, discrepancies exist where test protocols and material properties of coated paper impact the MVTR measurement. The measurement discrepancies can be explained by differences in local moisture concentration. Our study provides new insights on moisture vapor barrier assessment of waterborne coatings on paper and implications for achieving paper packages with improved barrier performance.