Microstructure and mechanical properties of free and restrained dried paper: a comprehensive investigation

Urstöger, Georg Johann; Kulachenko, Artem; Schennach, Robert; Hirn, Ulrich

doi:10.1007/s10570-020-03367-4

Cited by 22 publications

(23 citation statements)

References 22 publications

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“…While wetting and sorption obviously swell fibers, thereby increasing their diameter, the opposite process, drying, accomplishes more than simply reversing this process. Rather, the drying process also alters certain key properties of the fibers, such as water retention, fiber stiffness, and cohesion of the fiber network, which is a rather complex physical phenomenon. , Therefore, we conducted an experiment in which the same strip of paper was measured in a rotational experiment and then carefully dried under climate-controlled conditions (23 °C, 50% relative humidity) and finally centrifuged at a constant rotation speed of 2200 rpm for 30 min. Subsequently, another rotational experiment was performed, during which the same paper strip was rewetted.…”

Section: Resultsmentioning

confidence: 99%

Porosity Centrifuge: Determination of Pore Sizes of Swellable Porous Materials under Hypergravity

2021

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Porous materials are ubiquitous and essential for many processes in nature as well as in industry, and the need to produce them from renewable materials will definitely increase. A prominent example for such a fully recyclable and biogenic porous material is paper, a material that contains macropores formed in between the fibers as well as a large distribution of much finer pores on and within the fiber walls. While the determination of pore sizes is of central importance for the characterization of such materials, their determination is usually only possible with complex methodologies. The determination of pore sizes in the context of water has remained largely unsolved to date, in particular, if water-swellable materials are considered. Here, we introduce a completely new way of determining pore sizes of materials even under swelling conditions. Using a centrifugal device and studying the imbibition of water into paper at various centrifugal forces that oppose the capillary forces, we can access the mean pore size of different paper materials in an experimentally simple fashion. In addition, we can show that the pore size values obtained with our "centrifugal porosimetry" are consistent with the values obtained using other methods, usually much more involved methods. For this purpose, we measure wellcharacterized translucent macroporous materials using water, ranging from simple glass capillaries to standard filters and nitrocellulose membranes.

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Section: Resultsmentioning

confidence: 99%

Porosity Centrifuge: Determination of Pore Sizes of Swellable Porous Materials under Hypergravity

2021

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“…To test if the "transformation" really occurs at the sheet level, the hygro-expansion of the handsheets tested during the hydro-expansion experiments should be characterized afterwards. Furthermore, as generally known, the elastic stiffness of RD handsheets is larger than FD handsheets (Urstöger et al, 2020;Alzweighi et al, 2021). Hence, to test if not only the hygroscopic properties of RD handsheets "transform" after wetting, the elastic stiffness of the FD and RD handsheets before and after the the hydro-expansion cycle should be obtained.…”

Section: Sheet-scale Hydro-expansionmentioning

confidence: 99%

“…Using Equation 4, the sheet-scale expansion can directly be predicted, upon inserting the experimentally obtained fiber swelling properties, i.e. ll and tt , assuming a free fiber length of ∼ 50% (Wernersson et al, 2014;Borodulina et al, 2016;Urstöger et al, 2020), and adopting the fiber stiffness characteristics from literature with ν lt = ν tl equal to 0.022 (Magnusson and Östlund, 2013;Brandberg et al, 2020;Czibula et al, 2021). E t /E l is different for FD and RD, HW and SW fibers (Jentzen, 1964), therefore a range of values for E t /E l between 6 and 11 is studied here, covering the relevant range of values found in literature (Magnusson and Östlund, 2013;Brandberg et al, 2020;Czibula et al, 2021).…”

Section: Inter-fiber Bond Modelmentioning

confidence: 99%

“…Earlier X-ray CT measurements (Wernersson et al, 2014;Borodulina et al, 2016;Urstöger et al, 2020) were performed with a spatial resolution of only ∼ 0.5-1 µm, therefore, the measured bonded area may have been over-predicted. The effect of ∼ 50% bonding of the inter-fiber bonds may be approximated by assuming that the free fiber length is around 75% (i.e.…”

Section: Hypothesis To Explain the Transient Fiber And Sheet Hydro-ex...mentioning

confidence: 99%

“…As generally known, restrained dried (RD) paper yields a significantly lower hygro-expansion than freely dried (FD) paper (Salmén et al, 1987;Uesaka et al, 1992;Larsson and Wågberg, 2008;Urstöger et al, 2020;Vonk et al, 2023c). Salmén et al (1987) stated that during the paper formation process when the paper is fully saturated, the so-called "dislocated regions", which make up ∼ 50% of the cellulose micro-fibrils, are soft and stretched through the restrained drying procedure, but subsequently hardened during drying from a "wet" to a 90% RH state (Agarwal et al, 2013).…”

Section: Introductionmentioning

confidence: 97%

See 2 more Smart Citations

Transient hygro- and hydro-expansion of freely and restrained dried paper: the fiber-network coupling

Vonk¹,

Spreuwel²,

Anijs³

et al. 2023

Preprint

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The transient dimensional changes during hygro-expansion and hydro-expansion of freely and restrained dried, softwood and hardwood sheets and fibers is monitored, to unravel the governing micro-mechanisms occurring during gradual water saturation. The response of individual fibers is measured using a fullfield global digital height correlation method, which has been extended to monitor the transient hydroexpansion of fibers from dry to fully saturated. The hygro-and hydro-expansion is larger for freely versus restrained dried and softwood versus hardwood handsheets. The transient sheet-scale hydro-expansion reveals a sudden strain and moisture content step. It is postulated that the driving mechanism is the moisture-induced softening of the so-called "dislocated regions" in the fiber's cellulose micro-fibrils, unlocking further fiber swelling. The strain step is negligible for restrained dried handsheets, which is attributed to the "dislocated cellulose regions" being locked in their stretched configuration during restrained drying, which is supported by the single fiber hydro-expansion measurements. Finally, an inter-fiber bond model is exploited and adapted to predict the sheet-scale hygro-expansion from the fiber level characteristics. The model correctly predicts the qualitative differences between freely versus restrained dried and softwood versus hardwood handsheets, yet, its simplified geometry does not allow for more quantitative predictions of the sheet-scale hydro-expansion.

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Transient hygro- and hydro-expansion of freely and restrained dried paper: the fiber-network coupling

Vonk,

van Spreuwel,

Anijs

et al. 2024

Wood Sci Technol

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The transient dimensional changes during hygro-expansion and hydro-expansion of freely and restrained dried, softwood and hardwood sheets and fibers is monitored, to unravel the governing micro-mechanisms occurring during gradual water saturation. The response of individual fibers is measured using a full-field global digital height correlation method, which has been extended to monitor the transient hydro-expansion of fibers from dry to fully saturated. The hygro- and hydro-expansion is larger for freely versus restrained dried and softwood versus hardwood handsheets. The transient sheet-scale hydro-expansion reveals a sudden strain and moisture content step. It is postulated that the driving mechanism is the moisture-induced softening of the so-called ”dislocated regions” in the fiber’s cellulose micro-fibrils, unlocking further fiber swelling. The strain step is negligible for restrained dried handsheets, which is attributed to the ”dislocated cellulose regions” being locked in their stretched configuration during restrained drying, which is supported by the single fiber hydro-expansion measurements. Finally, an inter-fiber bond model is exploited and adapted to predict the sheet-scale hygro-expansion from the fiber level characteristics. The model correctly predicts the qualitative differences between freely versus restrained dried and softwood versus hardwood handsheets, yet, its simplified geometry does not allow for more quantitative predictions of the sheet-scale hydro-expansion.

show abstract

Microstructure and mechanical properties of free and restrained dried paper: a comprehensive investigation

Cited by 22 publications

References 22 publications

Porosity Centrifuge: Determination of Pore Sizes of Swellable Porous Materials under Hypergravity

Porosity Centrifuge: Determination of Pore Sizes of Swellable Porous Materials under Hypergravity

Transient hygro- and hydro-expansion of freely and restrained dried paper: the fiber-network coupling

Transient hygro- and hydro-expansion of freely and restrained dried paper: the fiber-network coupling

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