| 1. |
- Ghaffari, Roujin, 1994, et al.
(författare)
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Specific ion effects on lignin adsorption and transport through cellulose confinements
- 2024
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Ingår i: Journal of Colloid and Interface Science. - 1095-7103 .- 0021-9797. ; 653, s. 1662-1670
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Tidskriftsartikel (refereegranskat)abstract
- The presence of ions in a solution is anticipated to induce distinct effects on macromolecules. Consequently, the tuning of adsorption and mass transfer of lignin molecules can be achieved by incorporating ions with chaotropic or kosmotropic characteristics. This study examines the adsorption and mass transfer behavior of lignin molecules across model cellulose membranes in presence of ions from the Hofmeister series. Experimental investigations encompassed the use of diffusion cells to quantify lignin's mass transfer through the membranes, and quartz crystal microbalance with dissipation (QCM-D) monitoring was used for adsorption studies. Notably, at high ion concentrations, the mass transport rate of lignin was observed to be lower in the presence of highly hydrated (kosmotropic) sulfate ions, conforming to the Hofmeister series. Intriguingly, this relationship was not apparent at lower ion concentrations. Furthermore, QCM-D experiments indicated that lignin displayed higher adsorption onto the cellulose surface when exposed to less hydrated (chaotropic) nitrate anions. This behavior can be rationalized by considering the system's increased entropy gain, facilitated by the release of adsorbed ions and water molecules from the cellulose surface upon lignin adsorption. This study highlights the complexity of ion-specific effects on mass transfer and adsorption processes and their dependency on ion concentrations.
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| 2. |
- Hosseini, Seyedehsan, 1994, et al.
(författare)
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Alkyl ketene dimer modification of thermomechanical pulp promotes processability with polypropylene
- 2024
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Ingår i: Polymer Composites. - 1548-0569 .- 0272-8397. ; 45:1, s. 825-835
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Tidskriftsartikel (refereegranskat)abstract
- Alkyl ketene dimers (AKDs) are known to efficiently react with cellulose with a dual polarity in their structure: a polar component and a nonpolar component. AKD of three different carbon chain lengths, 4, 10, and 16 carbons have been synthesized, and thermomechanical pulp (TMP) fibers were modified by them. The modification of TMP fibers with AKD resulted in an increased water contact angle, showing the presence of the AKDs on the TMP fibers and a new carbonyl peak in the IR spectra, suggesting modification of the TMP fibers with AKD groups. Calculating the Hansen solubility parameters of AKD and AKD conjugated to TMP in polypropylene (PP) indicates improved compatibility, especially of longer chain AKD and TMP AKD. The rheological studies of the composites showed that the AKD with the longest carbon chain decreases the melt viscosity of the PP-TMP-AKD composite, which combined with the shape and the color of the extruded composite filaments indicates improved flow properties and reduced stress build up during processing. The research findings demonstrate the ability of AKD to enhance the dispersibility and compatibility of natural fibers with PP.
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| 3. |
- Hosseini, Seyedehsan, 1994, et al.
(författare)
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Reducing friction between metal and thermo-mechanical pulp using alkyl ketene dimers and magnesium stearate
- 2024
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Ingår i: Tribology International. - 0301-679X. ; 192
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Tidskriftsartikel (refereegranskat)abstract
- The friction between natural fibers and metal affects tool life, wear and tear and surface defects of extrudates. The ability of alkyl ketene dimer (AKD) and magnesium stearate (MgSt) to reduce coefficient of friction (COF) between thermomechanical pulp (TMP) and metal were determined at temperatures of 30, 100, and 180 °C and additive concentrations from 0.5 to 5 wt%. The AKD and MgSt were added to TMP sheets through spraying, followed by drying. ATR-FTIR and IR microscopy confirmed the presence of AKD and MgSt on the TMP. AKD addition at 2 wt%, consistently reduced the COF of TMP and metal, whereas MgSt reduced COF at 100 and 180 °C, only. No further reduction in COF was observed at 5 wt% of AKD or MgSt.
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| 4. |
- Ghaffari, Roujin, 1994, et al.
(författare)
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Effect of alkalinity on the diffusion of solvent-fractionated lignin through cellulose membranes
- 2023
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 30:6, s. 3685-3698
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Tidskriftsartikel (refereegranskat)abstract
- Mass transport of liberated lignin fragments from pits and fiber walls into black liquor is considered a determining step in the delignification process. However, our current understanding of the diffusion of lignin through cellulose and the influential parameter on this process is very limited. A comprehensive and detailed study of lignin mass transport through cellulosic materials is, therefore, of great importance. In this study, diffusion cell methodology is implemented to systematically investigate the transport of fractionated kraft lignin molecules through model cellulose membranes. Pulping is a complex process and lignin is very heterogenous material therefore to perform a more detailed study on lignin diffusion, we included an additional solvent fractionation step. One of the benefits of this method is that the setup can be adjusted to various experimental conditions allowing the complex chemical reactions occurring during pulping, which would affect the mass transfer of lignin, to be avoided. Here, the effects of the alkalinity of the aqueous solution and molecular weight of the kraft lignin molecules on their diffusion were investigated. Additionally, NMR spectroscopy, size exclusion chromatography, and UV/Vis spectroscopy were used to characterize the starting material and the molecules that passed through the membrane. Lignin molecules detected in the acceptor chamber of the diffusion cells had lower molecular weights, indicating a size fractionation between the donor and acceptor chamber. UV/Vis showed higher concentrations of ionized conjugated kraft lignin molecules in the acceptor chamber, which is a sign of chemical fractionation. This study suggests that the diffusion of lignin through small cellulose pores can be enhanced by decreasing the average molecular weight of the diffusing kraft lignin molecules and increasing alkalinity.
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| 5. |
- Ghaffari, Roujin, 1994
(författare)
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Mass transfer challenges in wood decomposition
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Even though the kraft cooking operation is more than 100 years old, the rate-determining step of this operation has not been fully elucidated. Recent studies point in the direction of mass transport of liberated lignin fragments from the fibers' walls into black liquor being influential in rate determination of kraft cooking. Thus, to further develop the kraft pulping operation, detailed knowledge of the mass transport events during pulping is of great importance. In this thesis, the diffusion of kraft lignin molecules through model cellulose membranes is studied by a diffusion cell methodology, where solubilized kraft lignin molecules diffuse from the donor chamber to the acceptor chamber through pores in the membrane. An advantage of using this method is that the influence of complex chemical reactions is eliminated while implementing various experimental parameters important for mass transport in the setup. Here we have investigated the effects of the membrane pore sizes, alkalinity of the solution, and size of the kraft lignin molecules on their diffusion through a porous cellulose membrane. Additionally, NMR spectroscopy, size exclusion chromatography, and UV/Vis spectroscopy techniques have been used to characterize the starting material and observe the differences between the starting material and the lignin molecules that have passed through the membrane. The average molecular weight of the species that diffused into the acceptor chamber after 168 hours was lower than that of the species in the donor chamber. The relative concentration of ionized conjugated kraft lignin molecules was higher in the acceptor chamber with the small pore membranes within the time span of the experiment. The results of this study show that the mass transport rate of lignin through a porous cellulose membrane is increased by increasing alkalinity and by decreasing molecular weight of the diffusing kraft lignin molecules. A possible explanation for the former is that the probability of forming associations in the solution is reduced at higher alkalinity levels. The latter can be explained by the higher diffusion coefficient of lower molecular weight molecules.
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| 6. |
- Ghaffari, Roujin, 1994
(författare)
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Mass Transport in Wood Disintegration: Implications for the Pulp and Paper Industry
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficient delignification and fractionation processes are essential in the pulp and paper industry. Mass transport events in wood fractionation are of great importance, specifically in two main stages, namely, the mass transport of chemicals into wood and the mass transport of degraded lignin molecules out of cellulose confinements. It has been previously suggested that the mass transport of lignin molecules through fibers is the rate-determining step in kraft pulping. This thesis first investigates the effects of pore sizes, the alkalinity of the solution, the molecular weight of lignin, and specific ion effects on the mass transport of lignin through model cellulose membranes using diffusion cells. Furthermore, the adsorption of lignin on cellulose substrates in the presence of salts chosen from the Hofmeister series was studied using a quartz crystal microbalance with dissipation monitoring (QCM-D). It was observed that mass transport rates through the cellulose membrane were enhanced by an increase in pore size, alkalinity of the solution, and a decrease in lignin molecular weight. Higher alkalinity of the solution decreases the association between the lignin molecules, which increases the mass transport. QCM-D measurements showed that the adsorption of lignin on cellulose was increased in the presence of chaotropic anions. This behavior can be rationalized by the system's entropy gain, facilitated by the release of adsorbed ions and water molecules from the cellulose surface upon lignin adsorption. The thesis also explores the rate-determining step in the ionoSolv fractionation process. To achieve a more homogeneous fractionation, the effects of temperature, water content, and vacuum on the impregnation of wood by ionic liquids (ILs) were further studied. This thesis not only highlights the complexity of mass transport events in wood fractionation but, by comparing the concentration of lignin released from dry wood, IL-impregnated wood, and previously reacted wood samples over time, has also revealed that the mass transport of the IL into wood is the rate-determining step.
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| 7. |
- Ghaffari, Roujin, 1994, et al.
(författare)
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Mass Transport of Lignin in Confined Pores
- 2022
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 14:10
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Tidskriftsartikel (refereegranskat)abstract
- A crucial step in the chemical delignification of wood is the transport of lignin fragments into free liquor; this step is believed to be the rate-limiting step. This study has investigated the diffusion of kraft lignin molecules through model cellulose membranes of various pore sizes (1-200 nm) by diffusion cells, where the lignin molecules diffuse from donor to acceptor cells through a membrane, where diffusion rate increases by pore size. UV-vis spectra of the donor solutions showed greater absorbance at higher wavelengths (similar to 450 nm), which was probably induced by scattering due to presence of large molecules/clusters, while acceptor samples passed through small pore membranes did not. The UV-vis spectra of acceptor solutions show a characteristic peak at around 350 nm, which corresponds to ionized conjugated molecules: indicating that a chemical fractionation has occurred. Size exclusion chromatography (SEC) showed a difference in the molecular weight (M-w) distribution between lignin from the donor and acceptor chambers. The results show that small pore sizes enable the diffusion of small individual molecules and hinder the transport of large lignin molecules or possible lignin clusters. This study provides more detail in understanding the mass transfer events of pulping processes.
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| 8. |
- Henrik-Klemens, Åke, 1990, et al.
(författare)
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The glass transition temperature of isolated native, residual, and technical lignin
- 2024
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Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 78:4, s. 216-230
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Tidskriftsartikel (refereegranskat)abstract
- The glass transition temperatures (T g) of native, residual, and technical lignins are important to lignocellulose pulping, pulp processing and side stream utilization; however, how the structural changes from native to residual and technical lignin influences T g has proven difficult to elucidate. Since the T g of macromolecules is greatly influenced by the molecular weight, low-molecular-weight fractions, such as milled wood lignin (MWL), are poor representatives of lignin in the cell wall. To circumvent this problem, lignins of both high yield and purity were isolated from Norway spruce and softwood kraft pulp using the enzymatic mild acidolysis lignin (EMAL) protocol. Technical softwood kraft lignin was also fractionated into groups of different molecular weights, to acquire lignin that spanned over a wide molecular-weight range. A powder sample holder for dynamic mechanical analysis (DMA), was used to determine the T g of lignins, for which calorimetric methods were not sensitive enough. The T gs of EMAL were found to be closer to their in situ counterparts than MWL.
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