| 1. |
- Francon, Hugo, et al.
(författare)
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Ambient-Dried, 3D-Printable and Electrically Conducting Cellulose Nanofiber Aerogels by Inclusion of Functional Polymers
- 2020
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028.
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a novel, green, and efficient way of preparing crosslinked aerogels from cellulose nanofibers (CNFs) and alginate using non-covalent chemistry. This new process can ultimately facilitate the fast, continuous, and large-scale production of porous, light-weight materials as it does not require freeze-drying, supercritical CO2 drying, or any environmentally harmful crosslinking chemistries. The reported preparation procedure relies solely on the successive freezing, solvent-exchange, and ambient drying of composite CNF-alginate gels. The presented findings suggest that a highly-porous structure can be preserved throughout the process by simply controlling the ionic strength of the gel. Aerogels with tunable densities (23–38 kg m−3) and compressive moduli (97–275 kPa) can be prepared by using different CNF concentrations. These low-density networks have a unique combination of formability (using molding or 3D-printing) and wet-stability (when ion exchanged to calcium ions). To demonstrate their use in advanced wet applications, the printed aerogels are functionalized with very high loadings of conducting poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:TOS) polymer by using a novel in situ polymerization approach. In-depth material characterization reveals that these aerogels have the potential to be used in not only energy storage applications (specific capacitance of 78 F g−1), but also as mechanical-strain and humidity sensors. © 2020 The Authors.
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| 2. |
- Li, Hailong, et al.
(författare)
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Development of mechanical properties of regenerated cellulose beads during drying as investigated by atomic force microscopy
- 2020
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Ingår i: Soft Matter. - : ROYAL SOC CHEMISTRY. - 1744-683X .- 1744-6848. ; 16:28, s. 6457-6462
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties as well as the size changes of swollen cellulose beads were measured in situ during solvent evaporation by atomic force microscopy (AFM) indentation measurement combined with optical microscopy. Three factors are proposed to govern the mechanical properties of the cellulose beads in the swollen state and during drying: (i) the cellulose concentration, (ii) the interaction between the cellulose entities, (iii) the heterogeneity of the network structure within the cellulose beads.
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| 3. |
- Li, Hailong, et al.
(författare)
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Macro- and microstructural evolution during drying of regenerated cellulose beads
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 14:6, s. 6774-6784
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Tidskriftsartikel (refereegranskat)abstract
- The macro- and microstructural evolution of water swollen and ethanol swollen regenerated cellulose gel beads have been determined during drying by optical microscopy combined with analytical balance measurements, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS). Two characteristic length scales, which are related to the molecular dimension of cellulose monomer and elongated aggregates of these monomers, could be identified for both types of beads by SAXS. For ethanol swollen beads, only small changes to the structures were detected in both the SAXS and WAXS measurements during the entire drying process. However, the drying of cellulose from water follows a more complex process when compared to drying from ethanol. As water swollen beads dried, they went through a structural transition where elongated structures changed to spherical structures and their dimensions increased from 3.6 to 13.5 nm. After complete drying from water, the nanostructures were characterized as a combination of rodlike structures with an approximate size of cellulose monomers (0.5 nm), and spherical aggregates (13.5 nm) without any indication of heterogeneous meso- or microporosity. In addition, WAXS shows that cellulose II hydrate structure appears and transforms to cellulose II during water evaporation, however it is not possible to determine the degree of crystallinity of the beads from the present measurements. This work sheds lights on the structural changes that occur within regenerated cellulose materials during drying and can aid in the design and application of cellulosic materials as fibers, adhesives, and membranes.
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| 4. |
- Mystek, Katarzyna, et al.
(författare)
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In Situ Modification of Regenerated Cellulose Beads : Creating All-Cellulose Composites
- 2020
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Ingår i: Industrial & Engineering Chemistry Research. - : AMER CHEMICAL SOC. - 0888-5885 .- 1520-5045. ; 59:7, s. 2968-2976
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Tidskriftsartikel (refereegranskat)abstract
- Developing more sustainable products requires innovative ways to utilize and modify renewable resources. Here, a simple one-step in situ modification of regenerated cellulose beads using cellulose nanocrystals (CNC) and dropwise precipitation of cellulose/N,N-dimethylacetamide and lithium chloride (DMAc/LiCI) solution is presented. A more condensed internal structure and increased surface roughness were observed when higher CNC concentrations were used in the precipitation media. Incorporation of CNCs significantly reduces the water holding capacity of the beads and simultaneously impacts the kinetics of drying. Beads modified using the highest CNC concentration (0.5 wt %) exhibited a reduction in the Young modulus by more than 20% and an increase in compressibility to failure by 10% compared with native beads. Overall, inclusion of nanoparticles during bead formation is a simple method that can tune the mechanical, structural, and swelling/drying behavior of cellulose beads and broaden their potential for different end-use applications such as separations and controlled release.
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| 5. |
- Mystek, Katarzyna, et al.
(författare)
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Wet-expandable capsules made from partially modified cellulose
- 2020
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Ingår i: Green Chemistry. - : ROYAL SOC CHEMISTRY. - 1463-9262 .- 1463-9270. ; 22:14, s. 4581-4592
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Tidskriftsartikel (refereegranskat)abstract
- Preparation of lightweight and biocompatible hollow capsules holds great promise for various advanced engineering applications. Here, we use a heterogeneously modified structure of cellulose, which on the molecular level increases the flexibility of the capsule shell, to form hollow capsules. These capsules expand in the wet state when they are exposed to an external stimulus, in the present case a decreased external pressure. The capsules were prepared by a dropwise precipitation of a propane-saturated solution of cellulose partially modified to dialcohol cellulose, dissolved in a mixture ofN,N-dimethylacetamide and lithium chloride, into a non-solvent. The mechanical properties of the capsules were determined by measuring the expansion of the capsules upon a controlled decrease in external pressure. In addition, indentation measurements using atomic force microscopy were used to independently quantify the moduli of the capsule walls. The results show that the wet, modified cellulose capsules are much softer and, upon the same pressure change, expand significantly more than those made from unmodified cellulose. The greatest expansion observed for the modified capsules was 1.9 times the original volume, which corresponds to a final density of the expanded capsules of about 14 kg m(-3). These capsules therefore hold great potential to form green and lightweight foam-like materials.
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