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ABSTRACT: Laboratory experiments with bleached kraft furnish were carried out to quantify the effects of major differences in electrical conductivity of papermaking process water (due to the addition of sodium sulfate) on the performance of various paperm

ABSTRACT: Laboratory experiments with bleached kraft furnish were carried out to quantify the effects of major differences in electrical conductivity of papermaking process water (due to the addition of sodium sulfate) on the performance of various papermaking additives. Batches of refined pulp were prepared with conductivity levels of 168 (tap water), 1000, and 10,000 ìS/cm. The absolute values of the calculated zeta potential, in various cases, were shown to decrease with increasing logarithm of electrical conductivity. The performance of retention aid systems, including cationic polyacrylamide (cPAM), were not adversely affected by increased salinity, even up to an electrical conductivity level of 10,000 ìS/cm. In fact, treatment involving sequential addition of cPAM and colloidal silica showed superior retention of mineral filler at the highest conductivity level. Likewise, combinations of papermaking additives that promote the dewatering of paper continued to perform well in furnish prepared with increasing salinity. The ability of various chemical systems to induce flocculation among papermaking fibers decreased moderately at the highest level of salinity considered.

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.

Dynamic CFD modeling of calcination in a rotary lime kiln with an external dryer, TAPPI Journal August 2023

ABSTRACT: Mid-kiln ring formation is a problem in lime kilns that may be related to fluctuations in the start location of calcination. To calculate fluctuations in bed and gas temperature profiles within a lime kiln with an external dryer, a dynamic two-dimensional (2D) axisymmetric computational fluid dynamics (CFD) gas model with a methane burner implemented in ANSYS Fluent, coupled by mass and heat balances to a one-dimensional (1D) bed model, was developed. The dynamic model was used to calculate changes in the location where calcination starts with fluctuations in operational conditions using pulp mill data. This model simulates radiative, convective, and conductive heat transfer between the gas, wall, and bed to determine the axial bed temperature in the kiln. The calcination reaction is described using a shrinking core model that allows for the prediction of the location at which calcination begins and the degree of calcination achieved. The solid motion within the kiln is modeled using Kramer’s equation modified for transient response. Steady-state and dynamic simulation results were compared to data from an industrial dry lime kiln, and good agreement was found. A sensitivity analysis was also performed to provide insight on how operating conditions and model variables impact the calcination location and degree of calcination. Of the variables examined, the fuel rate and the feed temperature had the largest impact on both the calcination location and degree of calcination in the kiln. Model predictions of a period of ring formation in the industrial kiln showed that the start location of calcination fluctuated by more than 2 m on either side of the mean of regular operation, warranting further investigation of the importance of these fluctuations on mid-kiln ring formation.

CFD and predictive modeling of temperature and calcination in a rotary lime kiln • Potential for steadier kiln operation, TAPPI Journal October 2024

ABSTRACT: Rotary lime kilns are used in the pulp and paper industry to calcine lime mud to lime. Lime kiln models provide a means to understand the complex phenomena occurring within the kiln to aid in problem-solving during operation. A two-dimensional (2D) computational fluid dynamics (CFD) and one-dimensional (1D) bed model was previously developed for steady-state and transient analysis. This study explores data extracted from the model over a longer time period. The simulated outlet gas and shell temperature are compared to measured data for validation. The capability of using the model to estimate the production rate, accounting for the residence time within the kiln, is discussed. The maximum refractory wall temperature is analyzed during operation. Fluctuations in the calcination location are compared to outer shell heat-map data to correlate the calcination location and ring formation and growth. The model results to date indicate that fluctuations in the calcination zone may contribute to problematic ring growth, though a direct correlation has yet to be established. Additionally, a method for steadier kiln control is introduced and discussed. A machine learning model is also developed to predict the calcination start location from industrial data and is compared to the CFD model for validation. This model can generate results quickly and without the need for knowledge in CFD software and theory. Good agreement is found between the CFD and machine learning model during operation, with a mean absolute error (MAE) of 0.46 m, a mean absolute percentage error (MAPE) of 0.92%, and a root mean square error (RMSE) of 1.17 m.

The influence of precoating layers on the performance of water-based barrier coatings, TAPPI Journal January 2025

Cellulose nanofibrils (CNF) on paper have been demonstrated to be an effective barrier against oxygen and grease and have been shown to improve the barrier performance of dispersion-based barrier coatings. The potential to produce paper grades that have good oxygen, grease, and moisture barrier properties is clear, but a better understanding of the synergies between CNF, other coating layers, and water-based barrier coatings (WBBC) is needed to optimize these systems. Different coat weights of a commercial WBBC were applied to papers that have a range of different qualities and thicknesses of CNF precoating layers. The same WBBC was also applied to pigmented coated paper, with various types of pigments and latex levels. Samples were characterized in terms of grease resistance, water vapor transmission rate (WVTR), and oxygen transmission rate (OTR) before and after folding. The results were contrasted to cases where the WBBC was applied to the paper with no precoating layer. When the WBBC is applied on a CNF layer or the pigmented coating layer, the performance of the WBBC for the water vapor barrier improves a significant amount compared to when the WBBC is applied to the base paper with no precoating layer. This improvement likely comes from these precoating layers filling in the large paper pores, which leads to the WBBC forming a continuous layer at low coat weights. Folding decreases the moisture barrier performance to some degree, but the grease resistance is not influenced by folding when a CNF precoating layer is involved. Oxygen barrier properties are moderate for the CNF layer alone and are less than 5 cm3/m2/day when WBBC is coated on the CNF layer. This result likely comes from the barrier coating’s ability to repair defects in the CNF layer to stop the easy passage of oxygen in defect regions of the sample.

Local delamination in pharmaceutical blister packages • A thermomechanical theory on buckling of heat-sealed composite laminates in flexible packaging, TAPPI Journal July 2025

ABSTRACT: Pharmaceutical blister packages consist of cavities made from a thick polymeric form foil and a thin aluminum lid foil. Heat-sealing technology is usually used to bond the lid foil to the form foil. Occasionally, the sealed area shows buckling defects of the lid foil, which allow contamination to enter into the cavity. A contaminated product is a worst-case scenario for pharmaceutical production and must be avoided. We discuss a thermomechanical theory on buckling defects in blister packages and derive strategies to avoid these. The theory is based on the assumption that the seal of a blister packaging behaves like a laminate of thin composite layers under compressive load. Literature research on buckling of thin laminated films, thermal behavior of polymers, and seal strength of heat-sealed polymers provides the technical and physical background to elaborate the theory. The theory comprises three elements: an initial condition regarding thermal load and precedent defects; a buckling condition; and a crack propagation condition. The plausibility of the theory is verified using model calculations and heat-seal tests. The paper concludes with strategies against buckling of heat-sealed lid foils and an outlook on other applications in laminating and coating of polymer films.

Materials performance considerations in hydrothermal liquefaction conversion of biomass, TAPPI Journal June 2025

ABSTRACT: Hydrothermal liquefaction (HTL) is a promising thermochemical route developed to convert woody biomass and biowaste to biochemicals and bio-oils. However, the operating conditions are rather harsh to biorefinery structural metallic components. These conditions include alkaline catalysts such as potassium carbonate (K2CO3); hot, pressurized (sub-critical) water reaction; and medium and aggressive anions chlorine (Cl•) and hydrogen sulfide (H•) released from biomass feedstocks. Thus, selection of suitable structural alloys for biorefinery components involves striking a balance between mechanical properties, corrosion resistance, and cost. Alloys currently being considered for this application include ferritic-martensitic steels and austenitic stainless steels. From a corrosion perspective in hot pressurized water, the former typically exhibits higher stress corrosion cracking resistance, whereas the latter exhibits higher corrosion resistance. This study reviews cost-effective corrosion control strategies aimed at increasing the chromium (Cr) content for protective surface oxide formation, as screened by testing in simulated HTL alkaline water, to support materials selection and design. Corrosion control strategies include surface modification (increasing surface Cr content), alloying (increasing bulk Cr content), and stainless-steel type (ferritic vs. austenitic). Of the alloys considered (including those subjected to surface modification), ferritic stainless steels exhibit a promising balance between corrosion and stress corrosion cracking resistance, adding another family of candidate alloys for structural biorefinery component materials selection and design.

Effect of xylan on the mechanical performance of softwood kraft pulp 2D papers and 3D foams, TAPPI Journal March 2025

ABSTRACT: Pulp fibers are paramount in paper products and have lately seen emerging use in fiber foams. Xylan, an integral component in pulp fibers, is known to contribute to paper strength, but its effect on the strength of pulp fiber foams remains less explored. In this study, we investigate the role of xylan in both 2D handsheets and 3D foams. For a softwood kraft pulp, we enzymatically removed 1% from pulp fibers and added 3% xylan to them by adsorption, corresponding to approximately a decrease of a tenth and an increase of a third of the total xylan content. The mechanical properties of 2D fiber networks, i.e., handsheets, made using the xylan-enriched pulp improved, particularly regarding tensile strength and Young’s modulus; however, the decrease in mechanical properties of handsheets made from enzymatically- treated xylan-depleted pulp was more pronounced. In 3D networks • pulp fiber foams, much less fiber-fiber contacts formed, and thus the mechanical properties were not as much influenced by removal of xylan. Furthermore, the presence of the required surfactant on the fibers, acting as debonding agent, overshadows any positive effect xylan might have on fiber-fiber bonding. We propose that the improved mechanical properties for the sheets result from a combination of an increased number of fiber-fiber bonds and higher sheet density, while the deterioration in mechanical properties of handsheets comprising enzymatically-treated fibers is caused by the opposite effect.

Setting priorities in CNF particle size measurement: What is needed vs. what is feasible, TAPPI Journal February 2023

Energy saving potential of interstage screen fractionation for production of board grade BCTMP, TAPPI Journal August 2023

Over the last few decades, the continuing decline in mechanical pulp-based grades has led pulp producers to modify operations and implement measures to reduce production costs in order to stay competitive. In spite of a considerable effort to reduce energy consumption, the latter is still a major portion of production costs in the process of making bleached chemithermomechanical pulp (BCTMP). In this study, we evaluated the impact of interstage screening fractionation (ISSF) and secondary refining strategy for producing BCTMP with the objective of reducing refining energy consumption while maintaining or improving bulk and strength properties. In the first step and to establish a baseline for a mill’s existing configuration, the collected primary refined pulp and reject streams from the ISSF were refined in a high consistency (HC) refiner to target freeness levels. The accepts and refined rejects streams were recombined, and their properties were compared to those of the refined primary pulp. The results showed that, at a given freeness of 400 mL and compared to the control case (without fractionation), the ISSF using an 0.070 in. basket followed by rejects refining could lead to about 25% energy saving in the second stage HC refining. Handsheet properties showed that utilization of ISSF could produce BCTMP with higher bulk and similar average fiber length and tear index. However, a slight reduction in tensile strength was observed. In the second set of trials, the primary refined pulp and the rejects from the ISSF using the 0.070 in. basket were refined by a low-consistency (LC) refiner. The results showed that, at the same freeness of 400 mL and compared to refined primary pulp, the ISSF saved about 26% in net LC refining energy. At a specific edge load (SEL) of 0.4 J/m, the produced pulp had similar bulk and strength properties compared to those of the control sample. A higher SEL of 0.6 J/m in LC refining could further decrease net refining energy consumption; however, it also led to reduction in fiber length, bulk, and strength properties.