| 1. |
- Ciftci, Göksu Cinar, et al.
(författare)
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Tailoring of rheological properties and structural polydispersity effects in microfibrillated cellulose suspensions
- 2020
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Ingår i: Cellulose. - : Springer Science+Business Media B.V.. - 0969-0239 .- 1572-882X. ; 27:16, s. 9227-9241
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Industrial production of low-charge microfibrillated cellulose (MFC) typically results in wide fibril size distributions. This polydispersity influences viscosity, overall colloidal stability, and rheological properties of MFC suspensions and gels in aqueous systems. In this work, a systematic rheological analysis is performed for industrially prepared MFC and fractions of different size distributions. Gel formation and flow characteristics (e.g., shear-thinning) of each fraction are examined under neutral and acidic conditions and compared with the unfractionated MFC suspension. The effects of size, aspect ratio, and surface charge on the rheology of semi-dilute MFC suspensions are discussed. The results demonstrate that particle size and aspect ratio distribution control the viscoelasticity and shear-thinning properties of MFC suspensions. An increased fraction of small diameter nanofibrils, by ex situ addition of the fine particles with high aspect ratio or removal of the coarsest particles (with lower aspect ratio) by fractionation, significantly enhances the storage modulus and the yield stress of the complex mixture, compared to the properties of the coarser fractions. New insights are also reported on the tailoring of the rheology of highly polydisperse fibrillar mixtures, where the rheological contributions of each fraction are discussed. Graphic abstract: [Figure not available: see fulltext.].
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| 2. |
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| 3. |
- Li, Lengwan, et al.
(författare)
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Ultrastrong Ionotronic Films Showing Electrochemical Osmotic Actuation
- 2023
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:45
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Tidskriftsartikel (refereegranskat)abstract
- A multifunctional soft material with high ionic and electrical conductivity, combined with high mechanical properties and the ability to change shape can enable bioinspired responsive devices and systems. The incorporation of all these characteristics in a single material is very challenging, as the improvement of one property tends to reduce other properties. Here, a nanocomposite film based on charged, high-aspect-ratio 1D flexible nanocellulose fibrils, and 2D Ti3C2Tx MXene is presented. The self-assembly process results in a stratified structure with the nanoparticles aligned in-plane, providing high ionotronic conductivity and mechanical strength, as well as large water uptake. In hydrogel form with 20 wt% liquid, the electrical conductivity is over 200 S cm−1 and the in-plane tensile strength is close to 100 MPa. This multifunctional performance results from the uniquely layered composite structure at nano- and mesoscales. A new type of electrical soft actuator is assembled where voltage as low as ±1 V resulted in osmotic effects and giant reversible out-of-plane swelling, reaching 85% strain.
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| 4. |
- Walther, Andreas, et al.
(författare)
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Best Practice for Reporting Wet Mechanical Properties of Nanocellulose-Based Materials
- 2020
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 21:6, s. 2536-2540
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Tidskriftsartikel (refereegranskat)abstract
- Nanocellulose-based materials and nanocomposites show extraordinary mechanical properties with high stiffness, strength, and toughness. Although the last decade has witnessed great progress in understanding the mechanical properties of these materials, a crucial challenge is to identify pathways to introduce high wet strength, which is a critical parameter for commercial applications. Because of the waterborne fabrication methods, nanocellulose-based materials are prone to swelling by both adsorption of moist air or liquid water. Unfortunately, there is currently no best practice on how to take the swelling into account when reporting mechanical properties at different relative humidity or when measuring the mechanical properties of fully hydrated materials. This limits and in parts fully prevents comparisons between different studies. We review current approaches and propose a best practice for measuring and reporting mechanical properties of wet nanocellulose-based materials, highlighting the importance of swelling and the correlation between mechanical properties and volume expansion.
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| 5. |
- Wohlert, Malin, et al.
(författare)
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Cellulose and the role of hydrogen bonds : not in charge of everything
- 2022
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Ingår i: Cellulose. - : Springer Nature. - 0969-0239 .- 1572-882X. ; 29:1, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- In the cellulose scientific community, hydrogen bonding is often used as the explanation for a large variety of phenomena and properties related to cellulose and cellulose based materials. Yet, hydrogen bonding is just one of several molecular interactions and furthermore is both relatively weak and sensitive to the environment. In this review we present a comprehensive examination of the scientific literature in the area, with focus on theory and molecular simulation, and conclude that the relative importance of hydrogen bonding has been, and still is, frequently exaggerated.
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| 6. |
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| 7. |
- Castro, Daniele Oliveira, et al.
(författare)
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The use of a pilot-scale continuous paper process for fire retardant cellulose-kaolinite nanocomposites
- 2018
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Ingår i: Composites Science And Technology. - : Elsevier Ltd. - 0266-3538 .- 1879-1050. ; 162, s. 215-224
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured materials are difficult to prepare rapidly and at large scale. Melt-processed polymer-clay nanocomposites are an exception, but the clay content is typically below 5 wt%. An approach for manufacturing of microfibrillated cellulose (MFC)/kaolinite nanocomposites is here demonstrated in pilot-scale by continuous production of hybrid nanopaper structures with thickness of around 100 μm. The colloidal nature of MFC suspensions disintegrated from chemical wood fiber pulp offers the possibility to add kaolinite clay platelet particles of nanoscale thickness. For initial lab scale optimization purposes, nanocomposite processing (dewatering, small particle retention etc) and characterization (mechanical properties, density etc) were investigated using a sheet former (Rapid Köthen). This was followed by a continuous fabrication of composite paper structures using a pilot-scale web former. Nanocomposite morphology was assessed by scanning electron microscopy (SEM). Mechanical properties were measured in uniaxial tension. The fire retardancy was evaluated by cone calorimetry. Inorganic hybrid composites with high content of in-plane oriented nanocellulose, nanoclay and wood fibers were successfully produced at pilot scale. Potential applications include fire retardant paperboard for semi structural applications and as reinforcement mats in molded thermoset biocomposites.
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| 9. |
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| 10. |
- Farahani, Saina Kishani, et al.
(författare)
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Experimental and Theoretical Evaluation of the Solubility/Insolubility of Spruce Xylan (Arabino Glucuronoxylan)
- 2019
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 20:3, s. 1263-1270
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 American Chemical Society. The molecular solubility of softwood arabinoglucuronoxylan (AGX) has been thoroughly investigated, and it has been shown that the chemical and physical structures of the extracted hemicellulose are not significantly influenced by different purification steps, but a transient molecular solubility of AGX was observed in aqueous media at low concentrations (1 g/L) when the dissolved macromolecules had a hydrodynamic diameter of up to 10 nm. A phase separation was detected when the concentration was increased to 15 g/L leading to an association of the smaller molecules into fractal structures with a considerably larger diameter, even though the dispersions were still transparent to ocular inspection. Dynamic Light Scattering and Cryo-Transmission Electron Microscopy showed dimensions in the range of 1000 nm. The phase separation of the sample was further characterized by estimating the χ-interaction parameter of AGX in water using the Flory-Huggins theory, and the results supported that water is a poor solvent for AGX. This behavior is crucial when films and hydrogels based on these biopolymers are made, since the association will dramatically affect barrier and mechanical properties of films made from these materials.
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