| 1. |
- Francon, Hugo, et al.
(author)
-
Ambient-Dried, 3D-Printable and Electrically Conducting Cellulose Nanofiber Aerogels by Inclusion of Functional Polymers
- 2020
-
In: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028.
-
Journal article (peer-reviewed)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.
|
|
| 2. |
- Li, Hailong, et al.
(author)
-
Development of mechanical properties of regenerated cellulose beads during drying as investigated by atomic force microscopy
- 2020
-
In: Soft Matter. - : ROYAL SOC CHEMISTRY. - 1744-683X .- 1744-6848. ; 16:28, s. 6457-6462
-
Journal article (peer-reviewed)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.
|
|
| 3. |
- Li, Hailong, et al.
(author)
-
Macro- and microstructural evolution during drying of regenerated cellulose beads
- 2020
-
In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 14:6, s. 6774-6784
-
Journal article (peer-reviewed)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.
|
|
| 4. |
- Li, Hailong, et al.
(author)
-
Understanding the Drying Behavior of Regenerated Cellulose Gel Beads : The Effects of Concentration and Nonsolvents
- 2022
-
In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:2, s. 2608-2620
-
Journal article (peer-reviewed)abstract
- The drying behavior of regenerated cellulose gel beads swollen with different nonsolvents (e.g., water, ethanol, water/ethanol mixtures) is studied in situ on the macroscopic scale with an optical microscope as well as on nanoscale using small-angle/wide-angle X-ray scattering (SAXS/WAXS) techniques. Depending on the cellulose concentration, the structural evolution of beads during drying follows one of three distinct regimes. First, when the cellulose concentration is lower than 0.5 wt %, the drying process comprises three steps and, regardless of the water/ethanol mixture composition, a sharp structural transition corresponding to the formation of a cellulose II crystalline structure is observed. Second, when the cellulose concentration is higher than 5.0 wt %, a two-step drying process is observed and no structural transition occurs for any of the beads studied. Third, when the cellulose concentration is between 0.5 and 5.0 wt %, the drying process is dependent on the nonsolvent composition. A three-step drying process takes place for beads swollen with water/ethanol mixtures with a water content higher than 20%, while a two-step drying process is observed when the water content is lower than 20%. To describe the drying behavior governed by the cellulose concentration and nonsolvent composition, a simplified phase diagram is proposed.
|
|
| 5. |
- Mystek, Katarzyna, et al.
(author)
-
In Situ Modification of Regenerated Cellulose Beads : Creating All-Cellulose Composites
- 2020
-
In: Industrial & Engineering Chemistry Research. - : AMER CHEMICAL SOC. - 0888-5885 .- 1520-5045. ; 59:7, s. 2968-2976
-
Journal article (peer-reviewed)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.
|
|
| 6. |
- Mystek, Katarzyna, et al.
(author)
-
The preparation of cellulose acetate capsules using emulsification techniques: High-shear bulk mixing and microfluidics
- 2023
-
In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 38:4, s. 593-605
-
Journal article (peer-reviewed)abstract
- This work describes an emulsification-solvent-evaporation method for the preparation of liquid-filled capsules made from cellulose acetate. Two different emulsification techniques were applied: bulk emulsification by high-shear mixing, and droplet generation using microfluidics. The bulk emulsification method resulted in the formation of oil-in-water emulsions composed of an organic mixture of isooctane and cellulose acetate in methyl acetate, and an aqueous phase of high-molecular-weight polyvinyl alcohol (PVA). Upon the solvent evaporation, the emulsion droplets evolved into isooctane-filled cellulose acetate capsules. In contrast, microfluidics led to the formation of monodisperse droplets composed of the aqueous PVA solution dispersed in the organic phase. Upon the solvent evaporation, the emulsion droplets evolved into water-filled cellulose acetate capsules. Owing to the thermoplastic properties of the cellulose acetate, the capsules formed with the bulk mixing demonstrated a significant expansion when exposed to an increased temperature. Such expanded capsules hold great promise as building blocks in lightweight materials.
|
|
| 7. |
|
|
| 8. |
- Mystek, Katarzyna
(author)
-
Use of Cellulose for the Preparation of Capsules and Beads with Molecularly Tailored Properties
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- The continuously increasing global production of petroleum-based polymers to meet the ever growing demand for plastics for use in a multitude of industrial sectors (e.g. packaging and textiles) has an impact on human health, climate change and the entire ecosystem. Therefore, there is a need to develop truly biodegradable, high-performance materials from renewable resources that can replace conventional plastics. These environmentally friendly alternative materials must possess similar properties to the materials they are replacing. The excellent mechanical properties, good chemical stability and straightforward functionalization of cellulose makes it an excellent candidate raw material that can initiate a transition away from petroleum-based plastics and toward more sustainable future.This thesis investigates the use of native and partially modified cellulose for the preparation of hollow or liquid-filled capsules and solid beads with unique and well-controlled structural and mechanical properties. The shaping of materials was made possible by the dissolution of cellulose in a suitable solvent, followed by its regeneration. Two different methods for preparing these cellulose-based materials are proposed: a solution–solidification method that creates millimeter-sized hollow capsules and solid beads, and an emulsification-solvent-evaporation method that results in the formation of micrometer scale liquid-filled capsules. The partial conversion of cellulose to dialcohol cellulose and cellulose acetate introduced flexibility and thermoplastic features to the cellulose materials. This resulted in the formation of stimuli-responsive capsules with properties suitable for different industrial applications; for example, in the production of next-generation lightweight materials. The hollow dialcohol-modified cellulose capsules exhibit a tendency, when wet, to expand to almost double their volume when exposed to a decreased external pressure, whereas the dry liquid-filled cellulose acetate capsules show a thermal expansion up to 60 times their original volume. Apart from the chemical modifications, the work discusses a method of altering the properties of cellulose beads by inclusion of cellulose nanocrystals, creating an all-cellulose composite material.The thesis also includes model studies focused on a better understanding of the evolution of the internal structure of regenerated cellulose beads during drying from different solvents. A combination of small-angle X-ray scattering, wide-angle X-ray scattering and atomic force microscopy indentation techniques allowed the monitoring of the macro- and micro-scale structural changes taking place within the beads, as well as a continuous evaluation of the mechanical properties of beads upon solvent evaporation. This work provides a fundamental understanding of the mechanisms and molecular interactions characteristic of the drying of cellulosic materials.
|
|
| 9. |
- Mystek, Katarzyna, et al.
(author)
-
Wet-expandable capsules made from partially modified cellulose
- 2020
-
In: Green Chemistry. - : ROYAL SOC CHEMISTRY. - 1463-9262 .- 1463-9270. ; 22:14, s. 4581-4592
-
Journal article (peer-reviewed)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.
|
|
| 10. |
- Mystek, Katarzyna, et al.
(author)
-
Wet-expandable cellulose-based capsules
- 2019
-
In: Abstracts of Papers of the American Chemical Society. - : AMER CHEMICAL SOC. - 0065-7727. ; 257
-
Journal article (other academic/artistic)
|
|
