The Effect of Void Structure on the Permeability of Fibrous Networks

Koponen, Antti; Ekman, Axel; Mattila, Keijo; Al-Qararah, Ahmad M.; Timonen, J.

doi:10.1007/s11242-017-0831-2

Cited by 17 publications

(13 citation statements)

References 46 publications

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“…When was 10 they reported apparent foam viscosities as much as 60% below that of water. As discussed above, Koponen et al (2017) found with X-ray tomography that at a porosity of 0.8, for example, the average pore diameter of a fiber sheet was 30 lm, which is clearly smaller than the typical diameter of bubbles. The porosity of the filtered sheet is here unknown during forming, but it seems probable that the constricted pore type flow of foam contributes to the observed low resistance of foam.…”

Section: Resultsmentioning

confidence: 81%

“…On the other hand, with similar density, the permeability of foam-formed sheets can be higher than water-formed sheets due to different pore structures. In Koponen et al (2017), for example, foam-formed fiber sheets had 30-60% higher permeability in the porosity region of 0.8-0.9. Figure 10 shows a schematic of two possible cases of the flow of Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The average pore size of foam formed fiber sheets was studied in Koponen et al (2017) with X-ray tomography. It was found that with porosity of 0.8-0.9 the average pore size was 30-60 lm.…”

Section: Resultsmentioning

confidence: 99%

“…In addition to surface tension, the observed improved dryness behavior of foam with increasing SDS dosage may be related to higher permeability of the sheet due to lower density before pressing (see Fig. 13) and a more open pore structure due to a higher number of large pores (Hjelt et al 2011;Koponen et al 2017). The air permeability of the final dry sheets, shown in Fig.…”

Section: Dryness Of Wet Sheets After Forming and Pressingmentioning

confidence: 95%

“…Displacement dewatering may also be improved in foam forming due to bubble surfaces wiping the droplets away from fiber surfaces. Sheet permeability may also be higher in foam forming due to a higher number of large pores (Hjelt et al 2011;Koponen et al 2017) and lower density. This would lead to higher flow rate of air, which improves displacement dewatering.…”

Section: Dryness Of Wet Sheets After Forming and Pressingmentioning

confidence: 99%

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Dewatering of foam-laid and water-laid structures and the formed web properties

et al. 2019

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The use of aqueous foams as a carrier fluid for pulp fibers instead of water has re-emerged in the paper and board industry in recent years. In foam forming, a surfactant is needed to reduce the surface tension of the carrier liquid and to create foam as a process fluid and flowing medium. This presents the following questions: (1) How do the water forming and foam forming processes differ? (2) How do the obtained wet/dry fibre sheets differ after forming and after wet pressing? (3) Which differences in the process behavior and sheet properties are due to the surfactant, and which are due to the presence of air bubbles in the flowing medium? The answers to these questions were sought by using an experimental academic approach and by applying a special dynamic

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Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 99%

“…The average pore size of foam formed fiber sheets was studied in Koponen et al (2017) with X-ray tomography. It was found that with porosity of 0.8-0.9 the average pore size was 30-60 lm.…”

Section: Resultsmentioning

confidence: 99%

Section: Dryness Of Wet Sheets After Forming and Pressingmentioning

confidence: 95%

Section: Dryness Of Wet Sheets After Forming and Pressingmentioning

confidence: 99%

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Dewatering of foam-laid and water-laid structures and the formed web properties

et al. 2019

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Design-driven integrated development of technical and perceptual qualities in foam-formed cellulose fibre materials

et al. 2017

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Potentiometric back titration as a robust and simple method for specific surface area estimation of lignocellulosic fibers

et al. 2021

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The specific surface area (SSA) of cellulosic or lignocellulosic fibers is seldom reported in the recent literature on papermaking, despite its close relation with the degree of refining and other key pulp properties. Amidst outdated assays (Pulmac permeability test) and methods that, while accurate, are of doubtful usefulness for papermaking purposes (N2 adsorption–desorption), we suggest a methodology based on the cationic demand. A commonly used cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC), became adsorbed onto thermomechanical pulp samples. Then, a potentiometric back titration with an anionic polyelectrolyte measured the cationic demand, expressed as microequivalents of PDADMAC per gram of pulp. Multiplying this value by the surface area of a microequivalent of polymer, considering rod-like conformation in the case of minimum ionic strength, yielded the SSA of the lignocellulosic pulp. Our system assumes that the quaternary ammonium groups were anchored through electrostatic and ion–dipole interactions. Measuring the carboxyl content allowed for discriminating between both kinds of forces. Finally, the model could be validated by plotting the estimated SSA values against the Schopper-Riegler degree, attaining high correlation coefficients (R2 ~ 0.98). Owing to the high molecular weight of the polyelectrolyte of choice (107 kDa), and more particularly in the case of fine-free pulps, SSA values estimated from the cationic demand were consistently lower than those from dye (Congo red) sorption. Instead of being a drawback, the limited diffusion of PDADMAC through fibers can enable papermakers to attain a more helpful quantification of the available surfaces in operations with low residence times.

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The Effect of Void Structure on the Permeability of Fibrous Networks

Cited by 17 publications

References 46 publications

Dewatering of foam-laid and water-laid structures and the formed web properties

Dewatering of foam-laid and water-laid structures and the formed web properties

Design-driven integrated development of technical and perceptual qualities in foam-formed cellulose fibre materials

Potentiometric back titration as a robust and simple method for specific surface area estimation of lignocellulosic fibers

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