| 1. |
- Cifelli, M., et al.
(författare)
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N-15-C-13 Dipole Couplings in Smectic Mesophase of a Thermotropic Ionic Liquid
- 2018
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Ingår i: Applied Magnetic Resonance. - : SPRINGER WIEN. - 0937-9347 .- 1613-7507. ; 49:6, s. 553-562
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Tidskriftsartikel (refereegranskat)abstract
- Unique combination of ionic conductivity and anisotropic physical properties in ionic liquid crystals leads to new dynamic properties exploited in modern technological applications. Structural and dynamics information at atomic level for molecules and ions in mesophases can be obtained by nuclear magnetic resonance (NMR) spectroscopy through the measurements of dipole-dipole spin couplings. While C-13-H-1 and N-15-H-1 dipolar NMR spectra can be routinely acquired in samples with natural isotopic abundance, recording N-15-C-13 dipolar NMR spectra is challenging because of the unfavourable combination of two rare isotopes. In the present study, an approach to measure N-15-C-13 dipole-dipole NMR spectra in static liquid crystalline samples with natural abundance is introduced. We demonstrate that well-resolved spectra can be recorded within 10 h of experimental time using a conventional NMR probe and a moderately strong magnetic field. The technique is applied to a thermotropic smectic mesophase formed by an ionic liquid with imidazolium-based organic cation.
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| 2. |
- Cifelli, M., et al.
(författare)
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NMR investigation of a thermotropic liquid crystal showing isotropic-isotropic'-(columnar)-cubic phase transitions
- 2017
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Ingår i: Molecular Crystals and Liquid Crystals. - : Taylor and Francis Inc.. - 1542-1406 .- 1563-5287. ; 649:1, s. 20-30
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report a first detailed study of the mesophasic behaviour of the calamitic liquid crystal, a (4,4′-bis(4″-carboxybelzyloxy)biphenyl derivate, labelled 9/2 RS/RS, showing an isotropic-isotropic-(columnar)-cubic phase behaviour on cooling. 1H NMR diffusometry allowed to distinguish between the two isotropic phases in terms of diffusion characterized by different Arrhenius activation energy, while 13C NMR static measurements and 2H NMR investigations were of help in understanding the orientational ordering properties of the metastable columnar phase and confirmed the isotropic state of the sample in the cubic phase.
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| 3. |
- Dvinskikh, Sergey, 1963-
(författare)
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Chapter 13 : Characterization of Liquid-crystalline Materials by Separated Local Field Methods
- 2018
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Ingår i: New Developments in NMR. - Cambridge : Royal Society of Chemistry. ; , s. 391-423
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Bokkapitel (refereegranskat)abstract
- A unique feature of liquid crystals is a high degree of molecular mobility combined with orientational and positional order. Solid-state NMR contributes to fundamental understanding of diverse molecular organizations and complex dynamic processes in these exciting materials. The focus of this chapter is on the development and application of advanced solid-state NMR methodologies for liquid crystal studies, with emphasis on techniques for measuring anisotropic spin couplings. The discussion centers on applications of separated dipolar local field NMR spectroscopy, which is used in an increasing number of directions in studies of novel liquid-crystalline materials for emerging technological applications.
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| 4. |
- Dvinskikh, Sergey, 1963-, et al.
(författare)
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Moisture content profiles and uptake kinetics in wood cladding materials evaluated by a portable nuclear magnetic resonance spectrometer
- 2011
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280. ; 6:3, s. 119-127
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Tidskriftsartikel (refereegranskat)abstract
- We have evaluated the capability of nuclear magnetic resonance (NMR) technology based on small portable magnets for in situ studies of the local moisture content in wood. Low field and low resolution 1H NMR with a unilateral permanent magnet was used to monitor and map the moisture content of wood cladding materials of various types in a spatially resolved manner. The results show that portable NMR equipment based on small open-access permanent magnets can be successfully used for non-invasive monitoring of the moisture content in various extended wood specimens. The moisture content was measured with a depth resolution of 0.2 mm and a maximum penetration depth of 3 mm. This makes the technique suitable for e.g. in situ local moisture content measurements beneath a coating layer in the claddings and it is also possible to relate the moisture level to specific properties of the wood material.
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| 5. |
- Gradisek, Anton, et al.
(författare)
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Study of Liquid Crystals Showing Two Isotropic Phases by H-1 NMR Diffusometry and H-1 NMR Relaxometry
- 2019
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Ingår i: CRYSTALS. - : MDPI. - 2073-4352. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report a study of two thermotropic liquid crystalline samples showing a not common mesophase behavior. The samples, namely a di-benzyloxy biphenyl derivative labelled 9/2 RS/RS, and a bimesogenic liquid crystal labelled L1, show a direct transition between two isotropic phases followed, at lower temperatures, by the optically isotropic, 3D structured, cubic phase. These systems have been investigated by means of H-1 NMR diffusometry and H-1 NMR relaxometry in order to characterize their isotropic-isotropic'-cubic mesophase behavior, mainly on the dynamic point of view. In particular, the temperature trend of the self-diffusion coefficients measured for both samples allowed us to significantly distinguish between the two isotropic phases, while the temperature dependence of the H-1 spin-lattice relaxation time (T-1) did not show significant discontinuities at the isotropic-isotropic' phase transition. A preliminary analysis of the frequency-dependence of H-1 T-1 at different temperatures gives information about the main motional processes active in the isotropic mesophases.
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| 6. |
- Grote, Fredrik, 1995-, et al.
(författare)
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Phase equilibrium, dynamics and rheology of phospholipid-ethanol mixtures : a combined molecular dynamics, NMR and viscometry study
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 25:23, s. 15905-15915
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Tidskriftsartikel (refereegranskat)abstract
- Binary mixtures of ethanol and phospholipids DOPC and DOPE have been investigated in a composition range relevant for topical drug delivery applications. This was done using a combined computer simulation and experimental approach where molecular dynamics simulations of ethanol-lipid mixtures with different compositions were performed. Several key properties including diffusion coefficients, longitudinal relaxation times, and shear viscosity were computed. In addition, diffusion coefficients, viscosities and NMR longitudinal relaxation times were measured experimentally for comparison and in order to validate the results from simulation. Diffusion coefficients and relaxation times obtained from simulations are in good agreement with results from NMR and computed viscosities are in reasonable agreement with viscometry experiments indicating that the simulations provide a realistic description of the ethanol-phospholipid mixtures. Structural changes in the simulated systems were investigated using an analysis based on radial distribution functions. This showed that the structure of ethanol-DOPC mixtures remains essentially unchanged in the investigated concentration range while ethanol-DOPE mixtures undergo structural rearrangements with the tendency for forming small aggregates on the 100 ns time scale consisting of less than 10 lipids. Although our simulations and experiments indicate that no larger aggregates form, they also show that DOPE has stronger aggregation tendency than DOPC. This highlights the importance of the character of the lipid headgroup for lipid aggregation in ethanol and gives new insights into phase equilibrium, dynamics and rheology that could be valuable for the development of advanced topical drug delivery formulations.
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| 7. |
- Jackalin, Lukas, et al.
(författare)
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Experimental strategies for 13C-15N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 20:34, s. 22187-22196
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Tidskriftsartikel (refereegranskat)abstract
- Direct dipolar spin couplings are informative and sensitive probes for a wide range of dynamic processes and structural properties at atomic, molecular and supramolecular levels in liquid crystals and other anisotropic materials. Usually, heteronuclear 13C-1H dipolar couplings in liquid crystals with natural 13C abundance are measured. Recording 13C-15N NMR dipolar spectra in unlabeled materials is challenging because of the unfavorable combination of two rare isotopes. Here we design and compare various experimental strategies to measure short- and long-range heteronuclear 13C-15N dipolar couplings in liquid crystalline samples with high molecular orientational order. New techniques were developed to record 13C and 15N spectra of naturally occurring 13C-15N spin pairs with increased signal intensity and spectral resolution while suppressing the signals of the uncoupled isotopes. Highly resolved 13C-15N dipolar spectra were recorded within an experimental time of a few hours. Coupling constants in a broad range of 10-1000 Hz between spins separated by up to five chemical bonds and distances of up to 5 Å were measured. Because of their relatively low demands on radio-frequency power levels, the experiments were easy to implement using conventional high-resolution solution-state NMR hardware. Experimental data were compared to the results of density functional theory and molecular dynamics computational analyses. The presented experimental methods to characterize the dipolar couplings in unlabeled materials provide novel routes to investigate molecular structure and dynamics in mesophases.
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| 8. |
- Jackalin, Lukas, et al.
(författare)
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Natural Abundance Nitrogen-15 NMR in Thermotropic Liquid Crystals With Cyano-Group
- 2017
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Ingår i: Zeitschrift fur physikalische Chemie (Munchen. 1991). - : WALTER DE GRUYTER GMBH. - 0942-9352 .- 2196-7156. ; 231:4, s. 795-808
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Tidskriftsartikel (refereegranskat)abstract
- We present natural abundance nitrogen-15 (NAN15) NMR spectroscopy in thermotropic liquid crystals. It is demonstrated that high resolution NAN15 NMR spectra in mesophases can be accurately recorded in non-spinning samples with a high orientational molecular order and strong anisotropic spin interactions. In this technique, due to low demand on radio-frequency decoupling power, standard solution-state probes can be used, which generally provide superior sensitivity and spectroscopic resolution in comparison to solid-state probes. We show that N-15 chemical shift anisotropy (CSA) can be used as a sensitive probe of molecular orientational dynamics in liquid crystals. This method is exploited here to measure the orientational molecular order parameter of the nematic 4-pentyl-4'-cyanobiphenyl (5CB). Since the nitrogen spectra are obtained from the molecules constituting the mesophase rather than from probe molecules, the information is direct and the analysis and interpretation is straightforward. Nitrogen CSA of immobilized molecules, required in the analysis, is obtained using a DFT calculation. The approach provided consistent results for the order parameter in the nematic 5CB in the whole temperature range, in good agreement with literature data.
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| 9. |
- Majhi, Debashis, et al.
(författare)
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Insights into cation-anion hydrogen bonding in mesogenic ionic liquids : an NMR study
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:38, s. 23532-23539
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen-bonding interaction is studied in imidazolium-based mesogenic ionic liquids in their isotropic, smectic, and solid phases and in a nanoconfined state by proton solid-state nuclear magnetic resonance (NMR). In the smectic phase, the more basic anions form stronger hydrogen bonds. A small decrease of H-bonding in the mesophase with respect to that in the isotropic phase is associated with the presence of a layered assembly with high orientational order and limited conformational freedom. Hydrogen bond strength is not sensitive to the cation structural modification as long as the aprotic nature of the material is preserved. The strong cation-anion hydrogen bonding observed in the smectic phases provides direct support for the presence of ionic sublayers which form in ionic liquid crystals regardless of the location and alignment of the charged group in the cation, particularly irrespective of whether the charged group occupies a terminal or central position in the cation structure. A comparison of the results obtained in isotropic, liquid-crystalline, and solid states shows that in the bulk materials the dynamic state of ions ranging from high reorientational and translational freedom to partial orientation and positional order to full immobilization, respectively, has no strong impact on the cation-anion hydrogen bond strength. On the other hand, nanoconfinement of ionic liquid crystals led to hydrogen bond disruption due to competing interactions of anions with a solid interface.
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| 10. |
- Majhi, Debashis, et al.
(författare)
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Ion conformation and orientational order in a dicationic ionic liquid crystal studied by solid-state nuclear magnetic resonance spectroscopy
- 2021
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Ingår i: Scientific Reports. - : NATURE RESEARCH. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Ionic liquids crystals belong to a special class of ionic liquids that exhibit thermotropic liquid-crystalline behavior. Recently, dicationic ionic liquid crystals have been reported with a cation containing two single-charged ions covalently linked by a spacer. In ionic liquid crystals, electrostatic and hydrogen bonding interactions in ionic sublayer and van der Waals interaction in hydrophobic domains are the main forces contributing to the mesophase stabilization and determining the molecular orientational order and conformation. How these properties in dicationic materials are compared to those in conventional monocationic analogs? We address this question using a combination of advanced NMR methods and DFT analysis. Dicationic salt 3,3 '-(1,6-hexanediyl)bis(1-dodecylimidazolium)dibromide was studied. Local bond order parameters of flexible alkyl side chains, linker chain, and alignment of rigid polar groups were analyzed. The dynamic spacer effectively "decouples" the motion of two ionic moieties. Hence, local order and alignment in dicationic mesophase were similar to those in analogous single-chain monocationic salts. Bond order parameters in the side chains in the dicationic smectic phase were found consistently lower compared to double-chain monocationic analogs, suggesting decreasing contribution of van der Waals forces. Overall dication reorientation in the smectic phase was characterized by low values of orientational order parameter S. With increased interaction energy in the polar domain the layered structure is stabilized despite less ordered dications. The results emphasized the trends in the orientational order in ionic liquid crystals and contributed to a better understanding of interparticle interactions driving smectic assembly in this and analogous ionic mesogens.
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| 11. |
- Majhi, Debashis, et al.
(författare)
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NMR Spectroscopic Studies of Cation Dynamics in Symmetrically-Substituted Imidazolium-Based Ionic Liquid Crystals
- 2020
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Ingår i: International Journal of Molecular Sciences. - : MDPI. - 1661-6596 .- 1422-0067. ; 21:14
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Tidskriftsartikel (refereegranskat)abstract
- Ionic liquid crystals (ILCs) present a new class of non-molecular soft materials with a unique combination of high ionic conductivity and anisotropy of physicochemical properties. Symmetrically-substituted long-chain imidazolium-based mesogenic ionic liquids exhibiting a smectic liquid crystalline phase were investigated by solid state NMR spectroscopy and computational methods. The aim of the study was to reveal the correlation between cation size and structure, local dynamics, and orientational order in the layered mesophase. The obtained experimental data are consistent with the model of a rod-shaped cation with the two chains aligned in opposite directions outward from the imidazolium core. The alignment of the core plane to the phase director and the restricted conformations of the chain segments were determined and compared to those in single-chain counterparts. The orientational order parameterS similar to 0.5-0.6 of double-chain ionic liquid crystals is higher than that of corresponding single-chain analogues. This is compatible with the enhanced contribution of van der Waals forces to the stabilization of smectic layers. Increased orientational order for the material with Br(-)counterions, which exhibit a smaller ionic radius and higher ability to form hydrogen bonds as compared to that of BF4-, also indicated a non-negligible influence of electrostatic and hydrogen bonding interactions. The enhanced rod-shape character and higher orientational order of symmetrically-substituted ILCs can offer additional opportunities in the design of self-assembling non-molecular materials.
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| 12. |
- Majhi, Debashis, et al.
(författare)
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Sign determination of dipolar couplings in liquid crystals by off-magic-angle sample spinning
- 2021
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 781
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Tidskriftsartikel (refereegranskat)abstract
- Dipolar NMR spectroscopy is a powerful analytical tool to study structural and dynamic properties of rigid and soft solids at the molecular level. While magnitudes of dipolar couplings can be determined from spectral splittings, signs of the constants are unavailable. A method to determine the signs of the dipolar couplings in liquid crystals is presented. Sign information is directly obtained from one-dimensional NMR spectra in samples spinning at an angle slightly misset from the magic angle. The approach is used to develop an experimental strategy for sign-sensitive measurements of heteronuclear dipolar couplings in anisotropic soft materials.
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| 13. |
- Matveev, V. V., et al.
(författare)
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Investigation of Melts of Polybutylcarbosilane Dendrimers by 1H NMR Spectroscopy
- 2017
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Melts of polybutylcarbosilane (PBC) dendrimers from third (G3) up to sixth (G6) generations are investigated by 1H NMR spectroscopy in a wide temperature range up to 493 K. At room temperature, NMR spectra of G3-G5 dendrimers exhibit resolved, solution-like spectra ("liquid" phase). In contrast, the spectrum of the G6 dendrimer is characterized by a single unresolved broad line at whole temperature range, which supports the presence of an anomalous phase state of G6 at temperatures higher than glass transition temperature. For the first time, an unexpected transition of G5 dendrimer from a molecular liquid state to an anomalous state/phase upon temperature increase has been detected using NMR data. Specifically, an additional wide background line appears in the G5 spectrum above 473 K, and this line corresponds to a G5 state characterized by restricted molecular mobility, i.e., a state similar to the "anomalous" phase of G6 melt. The fraction of the G5 dendrimers in "anomalous" phase at 493 K is approximately 40%. Analysis of the spectral shapes suggests that changes in the G5 dendrimers are reversible with temperature.
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| 14. |
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| 15. |
- Sophonrat, Nanta, et al.
(författare)
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Ex Situ Catalytic Pyrolysis of a Mixture of Polyvinyl Chloride and Cellulose Using Calcium Oxide for HCl Adsorption and Catalytic Reforming of the Pyrolysis Products
- 2019
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society. - 0888-5885 .- 1520-5045. ; 58:31, s. 13960-13970
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Tidskriftsartikel (refereegranskat)abstract
- In the context of chemical recycling of mixed plastics and paper, multitemperature step pyrolysis has shown good potential for the separation of oxygenated products from hydrocarbons. Here, we report results of an investigation of the first pyrolysis step at low temperature, which involves the dehydrochlorination of polyvinyl chloride (PVC) and the pyrolysis of cellulose, the main component of paper. Calcium oxide (CaO), selected for its chloride adsorption ability and its catalytic activity on biooil deoxygenation, was used for upgrading the downstream products from the pyrolysis. Additionally, we studied the performance of CaO for the simultaneous adsorption of HCl and for reforming cellulose pyrolysates in the temperature range of 300-600 °C with feedstock to CaO ratios of 1:0.2, 1:0.4, and 1:1. It was found that the suitable catalytic temperature for HCl and acetic acid adsorption is lower than 400 °C. This is due to the desorption of HCl from CaCl2 and Ca(OH)Cl in the presence of water and CO2 at 400 °C and higher. A larger amount of CaO resulted in a more efficient reduction of acids and the organic liquids were found to have lower amounts of oxygen. A comparison between the cases of neat and mixed feedstock showed that pyrolysis of mixed feedstock produced more water, H2, CO, and polycyclic aromatic hydrocarbons (PAHs) when compared to the case of neat materials over CaO
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| 16. |
- Sophonrat, Nanta, et al.
(författare)
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Ex-situ catalytic pyrolysis of a mixture of PVC and cellulose using calcium oxide for HCl adsorption and catalytic reforming of the pyrolysis products
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the context of chemical recycling of mixed plastics and paper, multi-temperature step pyrolysis has shown good potential for the separation of oxygenated products from hydrocarbons. Here, we report results of an investigation of the first pyrolysis step at low temperature, which involves the dehydrochlorination of polyvinyl chloride (PVC) and the pyrolysis of cellulose—the main component of paper. Calcium oxide (CaO), selected for its chloride adsorption ability and its catalytic activity on biooil deoxygenation, was used for upgrading the downstream products from the pyrolysis. Additionally, we studied the performance of CaO for the simultaneous adsorption of HCl and for reforming cellulose pyrolysates in the temperature range of 300-600 °C with feedstock to CaO ratios of 1:0.2, 1:0.4 and 1:1. It was found that the suitable catalytic temperature for HCl and acetic acid adsorption is lower than 400 °C. This is due to the reaction of CaO with water that causes the desorption of HCl at temperatures above 400 °C. A larger amount of CaO resulted in a more efficient reduction of acids and the organic liquids were found to have lower amounts of oxygen. A comparison between the cases of neat and mixed feedstock showed that pyrolysis of mixed feedstock produced more water, H2, CO and polycyclic aromatic hydrocarbons (PAHs) when compared to the case of neat materials over CaO.
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| 17. |
- Subbotina, Elena, et al.
(författare)
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Aqueous synthesis of highly functional, hydrophobic, and chemically recyclable cellulose nanomaterials through oxime ligation
- 2022
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibril (CNF) materials are candidates for the sustainable development of high mechanical performance nanomaterials. Due to inherent hydrophilicity and limited functionality range, most applications require chemical modification of CNF. However, targeted transformations directly on CNF are cumbersome due to the propensity of CNF to aggregate in non-aqueous solvents at high concentrations, complicating the choice of suitable reagents and requiring tedious separations of the final product. This work addresses this challenge by developing a general, entirely water-based, and experimentally simple methodology for functionalizing CNF, providing aliphatic, allylic, propargylic, azobenzylic, and substituted benzylic functional groups. The first step is NaIO4 oxidation to dialdehyde-CNF in the wet cake state, followed by oxime ligation with O-substituted hydroxylamines. The increased hydrolytic stability of oximes removes the need for reductive stabilization as often required for the analogous imines where aldehyde groups react with amines in water. Overall, the process provides a tailored degree of nanofibril functionalization (2-4.5 mmol/g) with the possible reversible detachment of the functionality under mildly acidic conditions, resulting in the reformation of dialdehyde CNF. The modified CNF materials were assessed for potential applications in green electronics and triboelectric nanogenerators. Water is a standing challenge in the chemical modification of cellulose nanofibrils. Here, authors employ oxime-ligation to solve this by direct covalent chemistry on dialdehyde-CNF in water and assess the material for potential applications in green electronics and triboelectric nanogenerators.
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