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Rice straw-based sustainable food packaging material with improved strength and barrier properties: Development and characterization, TAPPI Journal October 2023
ABSTRACT: Sustainable food packaging paper with high barrier and strength properties was developed with rice straw nanocellulose materials. Pulping and bleaching of rice straw were performed using an organosolv pulping and DED (D: chlorine dioxide bleaching; E: sodium hydroxide extraction) bleaching sequence. Bleached rice straw pulp was refined to 90°SR using a laboratory Valley beater. The laboratory handsheets were prepared using pulp slurry at 40°SR and 90°SR. The handsheets of cellulose nanofibrils (CNFs) made of highly refined pulp (90°SR) were surface sized using alkyl ketene dimer (AKD) wax to increase the barrier properties of paper for selective food packaging applications. The paper samples were tested for mechanical, optical, surface, and barrier properties, including tensile index, burst index, tearing index, bending stiffness, elongation, porosity, apparent density, opacity, Cobb value, water vapor transmission rate (WVTR), oil and grease resistance, and contact angle. The refined pulp (90°SR) was analyzed using field-emission scanning electron microscopy (FE-SEM), and it was observed that the morphology of the developed fibers changes to the nanoscale (<100 nm) for at least one dimension. The particle size distribution of the refined pulp using DLS analyzer also confirmed the cellulose fibers to near nanoscale. It was concluded that nanofibers were formed by a high degree of the mechanical pulp refining process and found to be much more economical than alternative processes in this direction. The sample handsheets of CNFs showed good strength and barrier properties. The barrier properties further increased when surface sizing was done using low-cost, nontoxic, and biodegradable AKD wax.
Journal articles
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Using bleaching stage models for benchmarking hardwood ECF bleach plants, TAPPI Journal October 2023
ABSTRACT: Steady-state models estimated the performance of the D0(EOP)D1 bleach sequence at two mixed hardwood bleach plants in the southern United States. At Mill 1, the full sequence’s chlorine dioxide charge that brightens the pulp to ~84% ISO was monitored for two weeks. Mill 2 considered the partial sequence that brightens the pulp to ~86% ISO for nearly four weeks. Elevated levels of chlorine dioxide were linked to increased washer carryover in brownstock and extraction areas. For Mills 1 and 2, an extra 0.24% and 0.33% chlorine dioxide was consumed in the D0 stage. This extra bleach demand was equivalent to an additional 4.8 and 5.5 kappa load to the brownstock, respectively. Some differences were observed for the D1 stage. Mill 1 had extraction carryover that averaged 1.1 units higher than was measured, contributing to use of an extra 0.22% of chlorine dioxide. Mill 2 had extraction carryover that averaged between 0 and 0.7 kappa units and consumed up to 0.13% more chlorine dioxide. Another data set from Mill 2 showed high brownstock and extraction carryover, leading to ~0.90% more total chlorine dioxide usage to brighten to 84% ISO. Overall, this investigation illustrated that the models could be employed as benchmarks.
Journal articles
Magazine articles
Online monitoring of the size distribution of lime nodules in a full-scale operated lime kiln using an in-situ laser triangulation camera, TAPPI Journal June 2024
ABSTRACT: To maximize efficiency of the recausticizing process in a pulp mill, producing a reburned lime with high and consistent reactivity is process critical. Prior investigations have demonstrated a correlation between the reactivity of lime and its nodule size, as well as the dusting behavior of the kiln. Therefore, monitoring the nodule size produced in the lime kiln could be a promising indirect method to measure the performance of the lime kiln. The objective of this investigation was to evaluate the utility of a laser triangulation camera for online monitoring of nodule size distribution for the lime kiln. A series of full-scale trials were performed in a lime kiln of a kraft pulp mill in which a camera was installed at the exit conveyor to analyze the lime discharging from the kiln. The nodule size distribution was analyzed for correlation with the lime temperature, flue gas temperature, and rotational speed of the kiln. The monitoring demonstrated temporal stability, and the results showed that the lime temperature had the most significant effect on the nodule size. The rotational speed of the lime kiln and the flue gas temperature showed limited effect on nodule size, but they had significant impact on the specific energy demand. The overall conclusion of the study is that the camera methodology effectively correlates lime temperature with nodule size distribution, and it advocates for the methods of implementation in automating lime temperature control, facilitating the production of consistently reactive lime at a lower specific energy consumption.
Journal articles
Magazine articles
Factors affecting phosphorus uptake/dissolution during slaking and causticizing, TAPPI Journal March 2024
ABSTRACT: Hydroxide is regenerated in the recovery cycle of kraft pulp mills by the addition of lime (CaO) to green liquor. Phosphate in green liquor can react with the lime during slaking/causticizing. Total titratable alkali (TTA), sulfidity, the concentration of phosphate in the green liquor, temperature, and the liming ratio were all variables explored in this work to determine their influence on phosphorus uptake and dissolution. Experiments were also run in which the lime was slaked before being added to the green liquor to separate reactions with phosphate during slaking and reactions that occur during causticizing. Both reburnt lime and technical grade CaO were used. The experiment results indicate that phosphorus primarily reacts with slaked lime (Ca(OH)2), and that the final concentration of phosphate in the white liquor at the end of slaking and causticizing is nearly independent of the initial concentration of phosphorus and only mildly dependent on the carbonate concentration in the green liquor. There do appear to be differences in the rate at which phosphate reacts with reburnt lime and technical grade CaO, though the reason for this was not determined.
Journal articles
Magazine articles
Z-directional testing of paperboard in combined tensile and compression loading, TAPPI Journal May 2024
ABSTRACT: The out-of-plane properties of paperboard are important in several converting applications such as printing, sealing, creasing, and calendering. A juxtaposed tensile and compression curve in the z direction (ZD) will, however, appear to have a kink or discontinuity at 0 stress. The purpose of the present work is to capture the continuous transition between tension and compression and to increase the understanding of the complex ZD properties of paperboard by cyclic testing. In this attempt to unify the ZD tensile and compressive behavior of paperboard, samples were laminated to the testing platens using heat seal laminate film. The method for adhering the samples was compared to samples that were laminated and glued to the testing platens. The edge effects of the cutting method were evaluated in compression testing with samples not attached to the testing platens. The flat slope seen in the initial part of the pure compression curve disappeared when the samples were laminated to the testing platens. The flat slope was instead replaced by a continuous response in the transition across 0 N. The stiffness in the transition region resembled the response in tensile testing. When the testing is cycled, the material exhibits a history dependence. Starting the cycle in either compression or tensile will show an effect on the stiffness at the transition, as well as the compressive stiffness. However, the ultimate tensile strength is unaffected.
Journal articles
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A novel unit operation to remove hydrophobic contaminants, TAPPI Journal April 2020
ABSTRACT: For mills making paper with recovered fiber, removal of hydrophobic contaminants is essential for trouble-free operation of paper machines. Significant cost savings on paper machine operation can be achieved by reducing deposits, which results in better quality, reduced downtime, increased fiber yield, and reduced energy consumption. Bubble nucleation separation (BNS) is a relatively new process for removing hydrophobic particles. When vacuum is applied to a slurry, dissolved gas bubbles nucleate on hydrophobic particles and drag them to the surface for easy removal. We constructed a 16-L batch unit to evaluate the effect of operating parameters on removal of hydrophobic particles, using statistical design of experiments. These results were used to guide our design of a 16-L continuous unit. We tested this unit on laboratory and mill samples. The removal of 60%•80% of hydrophobic particles was achieved with a low reject rate of < 2%.Following on this success, we built a 200-L pilot unit and tested it in our pilot plant. With promising results there, we installed the pilot unit at a commercial paper recycling mill. Over the course of several mill trials, we showed that it was possible to remove a considerable amount of suspended solids from paper machine white water with less than 2% rejects. Unfortunately, due to the unit only treating 50 L/min and the mill flow being 12000 L/min, we were not able treat a sufficient portion of the white water to know whether a large-scale implementation of BNS would improve paper machine runnability.
Journal articles
Magazine articles
Quantification of the degree of preference for different tissue products based on a hand-felt tissue test panel, TAPPI Journal May 2023
ABSTRACT: In this study, we successfully established a quantification model to determine the preference (PF) for different tissue products based on the results of a hand-felt tissue testing panel. The panel ascertained that products designed with four-ply tissues provided higher total tensile strength (TTS) and hand-felt surface softness (HSS) than did those of the three-ply, two-ply, and single-ply products.When practically tested with a tissue softness analyzer (TSA), the four-ply tissue product had a softness (TSA-HF) advantage; however, in human panel tests, more than half of the participants could not be sure of the hand-felt bulk softness (HBS) of the four-ply tissue product. This was mainly because when using the four-ply tissue, the hand-held test pad gave an overall perception distinctly different from those of the hand-held two- or three-ply products, which also differed from the flattened state of test pieces used in the instrumental softness tests. Users could distinctly feel that a product was safer (better TTS) and more comfortable (higher hand-held surface softness). Thus, the four-ply tissue product was accorded a higher preference.
Journal articles
Magazine articles
Utilization of kraft pulp mill residuals, TAPPI Journal February 2022
ABSTRACT: Kraft pulp mills produce on average about 100 kg of solid residuals per metric ton of pulp produced. The main types of mill waste are sludge from wastewater treatment plants, ash from hog fuel boilers, dregs, grits, and lime mud from causticizing plants and lime dust from lime kilns. Of these, about half is disposed of in landfills, which highlights the need and potential for waste recycling and utilization. Sludge is either incinerated in hog fuel boilers to generate steam and power or used in various forms of land application, including land spreading, composting, or as an additive for landfill or mine waste covers. The majority of hog fuel boiler ash and causticizing plant residues is landfilled. Alkaline residuals can be conditioned for use in land application, manufacture of construction materials, and production of aggregates for road work. This technical review summarizes residuals utilization methods that have been applied in pulp and paper mills at demonstration- or full-scale, and therefore may act as a guide for mill managers and operators whose goal is to diminish the costs and the environmental impact of waste management.
Journal articles
Magazine articles
Probing the molecular weights of sweetgum and pine kraft lignin fractions, TAPPI Journal June 2021
ABSTRACT: The present investigation undertook a systematic investigation of the molecular weight (MW) of kraft lignins throughout the pulping process to establish a correlation between MW and lignin recovery at different extents of the kraft pulping process. The evaluation of MW is crucial for lignin characterization and utilization, since it is known to influence the kinetics of lignin reactivity and its resultant physico-chemical properties. Sweetgum and pine lignins precipitated from black liquor at different pHs (9.5 and 2.5) and different extents of kraft pulping (30–150 min) were the subject of this effort. Gel permeation chromatography (GPC) was used to determine the number average molecular weight (Mn), mass average molecular weight (Mw), and polydispersity of the lignin samples. It was shown that the MW of lignins from both feedstocks follow gel degradation theory; that is, at the onset of the kraft pulping process low molecular weight-lignins were obtained, and as pulping progressed, the molecular weight peaked and subsequently decreased. An important finding was that acetobromination was shown to be a more effective derivatization technique for carbohydrates containing lignins than acetylation, the technique typically used for derivatization of lignin.
Journal articles
Magazine articles
Enzymatic treated viscose fibers functionalized by chitosan, TAPPI JOURNAL August 2018
Enzymatic treated viscose fibers functionalized by chitosan, TAPPI JOURNAL August 2018