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Multiple recycling of paperboard: Paperboard characteristics and maximum number of recycling cycles— Part I: Multiple recycling of corrugated base paper, TAPPI Journal November 2019
ABSTRACT: Paper for recycling is an important fiber source for the production of corrugated base paper. The change in production capacity toward more and more packaging papers affects the composition of paper for recy-cling and influences the paper quality. This research project investigated the influence of the multiple recycling of five different corrugated base papers (kraftliner, neutral sulfite semichemical [NSSC] fluting, corrugating medium, testliner 2, and testliner 3) on suspen-sion and strength properties under laboratory conditions. The corrugated board base papers were repulped in a low consistency pulper and processed into Rapid-Köthen laboratory sheets. The sheets were then recycled up to 15 times in the same process. In each cycle, the suspension and the paper properties were recorded. In particular, the focus was on corrugated board-specific parameters, such as short-span compression test, ring crush test, corrugat-ing medium test, and burst. The study results indicate how multiple recycling under laboratory conditions affects fiber and paper properties.
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Fate of phosphorus in the recovery cycle of the kraft pulping process, TAPPI Journal March 2020
ABSTRACT: The accumulation of nonprocess elements in the recovery cycle is a common problem for kraft pulp mills trying to reduce their water closure or to utilize biofuels in their lime kiln. Nonprocess elements such as magnesium (Mg), manganese (Mn), silicon (Si), aluminum (Al), and phosphorus (P) enter the recovery cycle via wood, make-up chemicals, lime rock, biofuels, and process water. The main purge point for these elements is green liquor dregs and lime mud. If not purged, these elements can cause operational problems for the mill. Phosphorus reacts with calcium oxide (CaO) in the lime during slaking; as a result, part of the lime is unavailable for slaking reactions. The first part of this project, through laboratory work, identified rhenanite (NaCa(PO4)) as the form of P in the lime cycle and showed the negative effect of P on the availability of the lime. The second part of this project involved field studies and performing a mass balance for P at a Canadian kraft pulp mill.
Journal articles
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Improving refining efficiency with deflocculation, TAPPI Journal May 2022
ABSTRACT: The ability to load a refiner requires the formation of a fiber mat between opposing refiner bars. One of the consequences of this is the formation of flocs that persist through the refiner grooves and exit the refiner. These flocs interfere with sheet strength, requiring additional energy to make up the strength deficit. In addition, flocs can initiate string formation, resulting in machine efficiency issues such as cross-machine profile deterioration and the downtime required to correct it. Novel refiner plate modifications have been shown to improve refining efficiency in otherwise identical refiner plates. Energy savings are typically around 15% of gross refining energy on the basis of the treated stock, although much higher reductions have also been seen. Addressing this previously underappreciated flaw in conventional refining enables greenhouse gas reduction and other benefits related to sheet strength and machine efficiency.
Journal articles
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Web instability in the open draw and the impact on paper machine efficiency, TAPPI Journal May 2022
ABSTRACT: Paper is most likely to break in the first open draw on a paper machine where it is unsupported, wettest, and weakest. Tension is applied to peel the web from the roll surface, as well as minimize web flutter in the open draw. The average tension is well below the breaking point and is often set by adjusting the speed difference between the press and the next machine element by visually observing the behavior of the web. However, machine direction variations caused by instabilities in the paper machine can cause tension swings that exceed the strength of the web. Measurement of the web’s release point from press rolls on pilot and commercial paper machines was used to identify the cause of tension instabilities. Variations in the speed of the paper machine drives and the work of adhesion from the press roll surface were identified as key factors. Fluctuations of paper moisture, which affects the elastic modulus and strength of the web, appear to be less important.
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Mechanistic aspects of nanocellulose•cationic starch•colloidal silica systems for papermaking, TAPPI Journal February 2023
ABSTRACT: Optimization of a chemical additive program for a paper machine can require attention to both colloidal charges and kinetic effects. This work considered an additive program with two negatively charged substances (nanofibrillated cellulose [NFC] and colloidal silica) and two positively charged items (cationic starch and cationic acrylamide copolymer retention aid). Results were shown to depend on charge interactions; however, that clearly was not the whole story. Some findings related to cationic demand, dewatering, fine-particle retention, and flocculation among fibers were best explained in terms of at least partly irreversible complexation interactions between the charged entities. Adjustments in ratios between oppositely charged additives, their sequences of addition, and effects of hydrodynamic shear levels all affected the results. In general, the most promising results were obtained at a cationic starch level of 0.25% to 0.5% based on sheet solids in systems where the cationic starch was used as a pretreatment for NFC.
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An analytical method to quantitatively determine the amount of polyamide epichlorohydrin (PAE) in paperboard and white water, TAPPI Journal February 2023,
ABSTRACT: Polyamide epichlorohydrin (PAE) is a permanent wet strength resin. When applied to paperboard, some amount of resin is retained in the sheet, and some is lost to the white water. An analytical method for quantifying the amount of PAE retained in the sheet and lost into the white water has been developed. This method hydrolyzes the PAE to adipic acid, which in turn is derivatized to diethyl adipate and quantified by pyrolysis gas chromatography•mass spectrometry (pyGCMS). In addition, the hydrolysis conditions of the PAE were studied by the Taguchi approach, and PAE material balances around the dry sheet and white water for 3 and 6 lb/ton PAE applications have been performed. The PAE resin recovery was 95.4% with 65.0% in the sheet for the 3 lb/ton PAE-charged paper-board, and the recovery was 96.7% with 36.1% in the sheet for the 6 lb/ton PAE-charged paperboard.
Journal articles
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How do mud balls form in lime kilns?, TAPPI Journal April 2023
ABSTRACT: Mud ball formation in lime kilns has been a persistent problem in many kraft mills, particularly for older kilns that are equipped with chains. A systematic laboratory study was conducted to examine how mud balls are formed and the key factors that affect ball formation. The results confirm the general mill experience that high moisture and high sodium contents in lime mud are the main contributing factors to ball formation. The high moisture content allows lime mud to agglomerate and grow to form balls, while the high sodium content helps make the balls hard and retain their shape. A ball formation mechanism is proposed to explain how mud balls form and grow near the kiln feed end.
Journal articles
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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.
Journal articles
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Measurement and control of extensional viscosity in barrier coating dispersions, TAPPI Journal November 2023
ABSTRACT: This study aimed to understand the effect of various rheological additives on the extensional viscosity of barrier coating dispersions, as well as to understand the role extensional viscosity plays in stabilizing a liquid curtain. The apparent extensional viscosity was measured using two devices that create accelerating flows: a capillary viscometer and an orifice rheometer. Additives tested include several polyvinyl alcohols, a high molecular weight polyethylene oxide, and carboxymethylcellulose. Extensional viscosity plays a significant role in stabilizing a liquid curtain, as it slows down hole expansion and prevents impurities and disturbances from causing holes in the first place. Some of the additives could substantially increase the extensional viscosity of the dispersions without increasing the shear viscosity outside the typical range of processability for a curtain coater. Some of the additives exhibited coil-stretch transition, meaning they start increasing extensional viscosity above a certain extension rate. Polymers with low chain lengths exhibited finite extensibility, which indicates the polymer chain has fully extended and cannot provide further extensional viscosity, even though the extending force is increased. Polymeric additives with stiff or branched chains significantly raised shear viscosity without increasing extensional viscosity. Both methods could reliably measure extensional viscosity in curtain coating barrier dispersions.
Journal articles
Magazine articles
Alkyl ketene dimer (AKD) sized paper reversion due to oxidative photodegradation, TAPPI Journal January 2024
ABSTRACT: Alkyl ketene dimer (AKD) is a sizing agent used in papermaking to increase the resistance of paper-board towards water penetration. The acquired hydrophobic property of the paper can be reversed due to the instability of the sizing agent. It is broadly known that AKD size reversion is due to migration, poor orientation, masking, or hydrolysis of the sizing agent. Unfortunately, the environmental parameters that cause this chemical instability are not well understood. Thus, the conditions that initiate or catalyze AKD size reversion and the mechanisms of AKD size reversion under different environmental conditions need to be investigated. In this study, six different experimental setups were used to investigate how temperature, daylight, fluorescent light, oxygen, and ultraviolet (UV) light affect AKD size reversion. Cobb values and pyrolysis gas chromatography-mass spectrometry (py-GCMS) results show that AKD size reversion is due to the degradation of the chemical in the presence of light and oxygen; temperature variations were found to accelerate reversion in the presence of light and oxygen. The oxidative photodegradation mechanism of the sizing agent is explored, and a possible mechanism is proposed.