| 1. |
- Georgouvelas, Dimitrios, 1985-
(författare)
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Modified and hybrid cellulose-based materials for water purification
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The need for clean water has led to the development of several different water treatment methods as well as to a large number of organic, inorganic, hybrid and/or composite materials that are used in these methods. Cellulose, being a highly abundant biopolymer with meritorious properties, such as high mechanical strength, tunable surface chemistry, high aspect ratio and surface area, to mention a few, is exploited in the current thesis for water treatment applications. Cellulose and its nanoscaled derivatives (i.e. cellulose nanocrystals and cellulose nanofibers) are modified or hybridized to achieve multiple functionalities.Cellulose and lignocellulose nanocrystals were successfully prepared by mechanical treatment from the residue of bioethanol production and were decorated with zwitterionic polymer grafts through controlled radical polymerization reactions. The presence of residual lignin and polymer grafts was investigated which showed that especially the polymer grafting can significantly improve the antibacterial and antifouling performance of nanocellulose.Functional cellulose-based membranes were prepared in a one-step water-based process. The membranes were evaluated as adsorbents for the removal of dyes and metal ions as well as metal-free catalysts for the decolorization of dyes Methylene Blue (MB) and Rhodamine B (RhB). The membranes exhibited maximum adsorption capacity of 78.6 mg/g for Co2+, up to 100 % of MB removal efficiency and up to 3-fold increase in the decolorization of MB.Both in-situ and ex-situ growth of ZIF-8 crystals was performed on the surface of cellulose and nanocellulose and cellulose/ZIF hybrid membranes were manufactured. The adsorption capacity of the membranes was tested with Cd2+, Cu2+, Fe3+, and Pb2+, exhibiting a maximum adsorption capacity of 354 mg/g for Cu2+. Furthermore, the membranes showed potential for use as self-standing electrode for the detection of Pb2+.Processing of cellulose/alginate composite hydrogels in the form of highly porous beads was successful. The surface of the beads was modified via in-situ TEMPO oxidation for the introduction of carboxyl groups. Adsorption of cationic contaminants as dyes and metal ions (MB and Cd2+ were used as models, respectively) was enhanced with in-situ modification. Removal of metal ions from the mining industry wastewater using modified cellulose/alginate hydrogel beads confirmed the potential of the adsorbent in complex water sources.All-cellulose flat sheets (100 × 20 cm) were produced via a water-based process using a Formette dynamic sheet former. The sheets exhibited excellent mechanical properties attributed to the alignment of the micro and nanofibers that this process offers. The adsorption performance of the sheets was evaluated both with Irgalite Blue RL and Irgalite Violet H dyes, which are highly used in paper and pulp industries as dyes models, and Fe3+, Mg2+, Cd2+, Co2+, Cr3+, and Mn2+ as metal ion models. A maximum removal efficiency of 83% for IB RL and maximum adsorption capacity of 737 mg/g for Mg2+.The work shows the potential of cellulose as a sustainable and scalable platform for the tailoring of multifunctional materials for water treatment with cationic pollutants removal, antifouling, antibacterial and sensing capabilities.
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| 2. |
- Ismail, Mostafa Y., et al.
(författare)
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Surface analysis of tissue paper using laser scanning confocal microscopy and micro-computed topography
- 2020
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 27:15, s. 8989-9003
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Tissue paper softness relies on two major factors, the bulk softness, which can be indicated by the elasticity of the sheet, and surface softness. Measurement of surface softness is complicated and often requires a multi-step process. A key parameter defining surface softness is the topography of the surface, particularly the crepe structure and its periodicity. Herein, we present a novel approach to measure and quantify the tissue paper surface crepe structure and periodicity based on the detection of waviness along the sample using laser scanning confocal microscopy (LSM) and X-ray tomography (XRT). In addition, field emission scanning electron microscope (FESEM) was used to characterize the tissue paper surface. We demonstrate that surface topography is directly correlated to the erosion of the doctor blade, which is used to remove the dry tissue paper from the Yankee cylinder. Because of its accuracy and simplicity, the laser confocal microscopy method has the potential to be used directly on the production line to monitor the production process of the tissue paper. XRT revealed more structural details of the tissue paper structure in 3D, and it allowed for the reconstruction of the surface and the internal structure of the tissue paper. Graphic abstract: [Figure not available: see fulltext.]
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| 3. |
- Jiang, Wen, et al.
(författare)
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Effect of Cellulose Nanofibrils on the Bond Strength of Polyvinyl Acetate and Starch Adhesives for Wood
- 2018
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Ingår i: BioResources. - : NC State University. - 1930-2126. ; 13:2, s. 2283-2292
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Tidskriftsartikel (refereegranskat)abstract
- Nanocellulose is a competitive reinforcement material for usein biocomposite structures and fibrous products. In this study, adhesive mixtures of dicarboxylic acid cellulose nanofibrils (CNF) were dispersed into commercial polyvinyl acetate (PVAc) and starch adhesives, whichwere applied to Norway spruce (Picea abies) to assess their performance in wood joining. Single-lap joints were prepared and tested with PVAc mixtures with0 to 0.64 wt% CNFand starch glue mixtures containing 0 to 1.07 wt% CNF. CNF suspensionshaving three concentrations(0.64, 0.96,and 1.28%)were compared. The results showed that the optimum amount of CNF, 0.48% suspensions, added to PVAc increased the average lap joint strength (EN 205:2003) by 74.5% when compared to control specimens with pure PVAc. Correspondingly, 0.96% CNF suspensions also enhanced the strength of starch adhesive by 34.5%. Lower and higher CNF concentrations showed clearly inferior performance. (PDF) Effect of Cellulose Nanofibrils on the Bond Strength of Polyvinyl Acetate and Starch Adhesives for Wood.
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| 4. |
- Liimatainen, Henrikki, et al.
(författare)
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High-Strength Nanocellulose-Talc Hybrid Barrier Films
- 2013
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 5:24, s. 13412-13418
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid organic inorganic films mimicking natural nacre-like composite structures were fabricated from cellulose nanofibers obtained from sequential periodate chlorite oxidation treatment and talc platelets, using a simple vacuum-filtration method. As a pretreatment, commercial talc aggregates were individualized into well-dispersed talc platelets using a wet stirred media mill with high-shear conditions to promote the homogeneity and mechanical characteristics of hybrids. The nanofiber talc hybrids, which had talc contents from 1 to 50 wt %, were all flexible in bending, and possessed tensile strength and Young's modulus values up to 211 +/- 3 MPa and 12 +/- 1 GPa, respectively, the values being remarkably higher than those reported previously for nanofibrillated cellulose talc films. Because of the lamellar and well-organized structure of hybrids in which the talc platelets were evenly embedded, they possessed a small pore size and good oxygen barrier properties, as indicated by the preliminary results. The talc platelets decreased the moisture adsorption of highly talc-loaded hybrids, although they still exhibited hydrophilic surface characteristics in terms of contact angles.
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| 5. |
- Niskanen, Ilpo, et al.
(författare)
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Determination of nanoparticle size using Rayleigh approximation and Mie theory
- 2019
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Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 201, s. 222-229
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Tidskriftsartikel (refereegranskat)abstract
- Accurate determination of the size of nanoparticles has an important role in many different scientific and industrial purposes, such as in material, medical and environment sciences, colloidal chemistry and astrophysics. We describe an effective optical method to determine the size of nanoparticles by analysis of transmission and scattering of visible spectral range data from a designed UV-Vis multi-spectrophotometer. The size of the nanoparticles was calculated from the extinction cross section of the particles using Rayleigh approximation and Mie theory. We validated the method using polystyrene nanospheres, cellulose nanofibrils, and cellulose nanocrystals. A good agreement was achieved through graphical analysis between measured extinction cross section values and theoretical Rayleigh approximation and Mie theory predictions for the sizes of polystyrene nanospheres at wavelength range 450-750 nm. Provided that Rayleigh approximation's forward scattering (FS)/back scattering (BS) ratio was smaller than 1.3 and Mie theory's FS/BS ratio was smaller than 1.8. A good fit for the hydrodynamic diameter of nanocellulose was achieved using the Mie theory and Rayleigh approximation. However, due to the high aspect ratio of nanocellulose, the obtained results do not directly reflect the actual cross-sectional diameters of the nanocellulose. Overall, the method is a fast, relatively easy, and simple technique to determine the size of a particle by a spectrophotometer. Consequently, the method can be utilized for example in production and quality control purposes as well as for research and development applications.
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| 6. |
- Niskanen, Ilpo, et al.
(författare)
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Determining the complex refractive index of cellulose nanocrystals by combination of Beer-Lambert and immersion matching methods
- 2019
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 235, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Nanocelluloses have received significant interest due to their unique structural, mechanical, and optical properties. Nanocellulose refractive indices can be used to indicate many crucial characteristics, such as crystallinity, transparency, and purity. Thus, accurate measurement is important. This study describes a new method to determine the wavelength dependent complex refractive index of cellulose nanocrystals (CNCs) by the measurement of light transmittance with a spectrophotometer. The data analysis is based on a combination of the Beer-Lambert and immersion liquid matching equations. The immersion liquid method's main advantage is that it is independent of particle shape and size. Moreover, the measurement is easy and relatively quick to perform. The present procedure is not restricted to the nanocellulose and could potentially be applied to other nanomaterials, such as hyphenate nanoparticle-based, lignin nanoparticles, nanopigments, biological entities, structural elements of dielectric metamaterials, and nanoparticle-based composites.
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| 7. |
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| 8. |
- Rodríguez, Martha Herrera
(författare)
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Nanostructured materials isolated from bio-residues, and their characterization
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of natural components in nanocomposites has continuously increased, due to environmental problems that are growing day by day. The use of bio-residues from forest industries to develop new materials will not only alleviate ecological problems but also affect the economy of forest industries positively.The aim of this work was to characterize cellulose nanowhiskers isolated from two different industrial bio-residues, one from bioethanol production and another from specialty cellulose production. Furthermore, the structure and permeability of thin films made of these nanowhiskers were studied. In the first study, the characteristics of nanowhiskers isolated from bioethanol residue were compared with nanowhiskers from microcrystalline cellulose (MCC). The nanowhiskers from ethanol residue had lower surface charge compared with whiskers obtained from MCC when analyzed by conductometric titration. The AFM microscopy showed that both cellulose nanowhisker suspensions presented individualized whiskers with diameters less than 10 nm. Nanowhiskers from ethanol residue showed higher relative crystallinity than the nanowhiskers from MCC, and the films made from both whiskers showed transparency in visual light. In addition, the nanowhiskers extracted from bio-residue were more thermally stable than the whiskers extracted from MCC, having a higher degradation onset temperature and maximum degradation temperature.In the second study, nanowhiskers isolated from two different bioresidues were compared. It was seen that both nanowhiskers suspensions (reject cellulose and ethanol residue) exhibited flow birefringence. Transmission electron microscopy study showed that the nanowhiskers extracted from the reject cellulose were slightly longer (377 nm) than the ones extracted from the ethanol residue (301 nm). The casted films of nanowhiskers from reject cellulose showed a stronger interference in the UV and visible region, compared with the other films. The comparative crystallinity was higher for reject cellulose nanowhiskers than for ethanol residue whiskers. Moreover, the thermal stability was slightly higher for the ethanol residue whiskers than for the reject cellulose whiskers. In the last study, cellulose nanowhiskers were isolated from the reject cellulose using hydrochloric and sulphuric acid hydrolysis processes with a aim to obtain different surface characteristics. Sulfuric acid whiskers had higher surface charge than the hydrochloric acid whiskers. Thin spin-coated films with two different configurations were prepared; one with alternate layers of poly(allylamine hydrochloride) (PAHCl) and cellulose nanowhiskers, and the second one with a single layer of PAHCl coated with 25 layers of whiskers. In addition, the film roughness, and surface charge of the whiskers was shown to increase the hydrophilic behavior of the films, being highest for a single layer of PAHCl coated with cellulose nanowhiskers. The gas permeability was measured and the coefficient was highest for hydrogen (H2) followed by helium (He), oxygen, (O2) and carbon dioxide (CO2) and nitrogen (N2). It was observed that the surface charge did not affect the gas permeability of the films and did not display selective gas barrier. The results showed that CNW can be extracted from ethanol residue and reject cellulose, and that these whiskers had similar characteristics as nanowhiskers obtained from other non-residual sources. This work has demonstrated that bio-residues can potentially be used as a source of new nanosize materials, thereby increasing the value of the forest resources.
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| 9. |
- Sethi, Jatin, et al.
(författare)
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Fast and Filtration-Free Method to Prepare Lactic Acid-Modified Cellulose Nanopaper
- 2021
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 6:29, s. 19038-19044
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Tidskriftsartikel (refereegranskat)abstract
- Dewatering in the preparation of cellulose nano-papers can take up to a few hours, which is a notable bottleneck in the commercialization of nanopapers. As a solution, we report a filtration-free method that is capable of preparing lactic acid-modified cellulose nanopapers within a few minutes. The bleached cellulose nanofibers (CNFs), obtained using a Masuko grinder, were functionalized by sonication-assisted lactic acid modification and centrifuged at 14 000 rpm to achieve a doughlike, concentrated mass. The concentrated CNFs were rolled into a wet sheet and dried in a vacuum drier to obtain nanopapers. The nanopaper preparation time was 10 min, which is significantly faster than the earlier time period reported in the literature (up to a few hours of preparation time). The mechanical properties of nanopaper were comparable to the previous values reported for nanopapers. In addition, the method was successfully used to prepare highly conductive functional nanopapers containing carboxylated multiwalled carbon nanotubes.
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| 10. |
- Taheri, Hesam, et al.
(författare)
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One-Step Twin-Screw Extrusion Process to Fibrillate Deep Eutectic Solvent-Treated Wood to Be Used in Wood Fiber-Polypropylene Composites
- 2021
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 9:2, s. 883-893
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Tidskriftsartikel (refereegranskat)abstract
- Bio-based wood materials are preferable for composites because of their sustainability, but adequately dispersing wood fibers in polymers can be difficult and costly. Our approach was to pretreat the wood with a green solvent system, allowing the composite to be extruded in a single step, simplifying the process, and reducing the overall cost. This study investigates the fibrillation of untreated wood sawdust (W) and deep eutectic solvent-treated wood sawdust (DESW) using a one-step twin-screw extrusion (TSE) process. The results of the analysis of wood fractions and optical microscopy confirmed that the one-step extrusion process resulted in fibrillation of both treated and untreated wood material. The width of the original wood particles was reduced by more than 99% after a one-step TSE for both untreated and DES-treated wood. The size reduction of the DESW was slightly greater than that of the untreated wood, and fibrillation was further confirmed by rheological analysis. The fibrillated wood was then compounded with polypropylene (PP) to produce a wood fiber-polypropylene composite with 50 wt % wood content. The elastic modulus of both untreated and treated extruded composites was higher than that of neat PP. The tensile strength and strain at break for the DESW-PP composite slightly increased in comparison to the untreated W-PP composite. Furthermore, DES treatment of wood resulted in a darker color and increased hydrophobicity of the material.
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| 11. |
- Thomas, Reny Thankam, et al.
(författare)
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Size exclusion and affinity-based removal of nanoparticles with electrospun cellulose acetate membranes infused with functionalized cellulose nanocrystals
- 2022
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- Membrane filtration and affinity-based adsorption are the two most used strategies in separation technologies. Here, µm-thick multifunctional and sustainable composite membranes of electrospun cellulose acetate (CA) infused with functionalized, anionic, and cationic cellulose nanocrystals (CNCs) with enhanced wettability, tensile strength, and excellent retention capacities were designed. CNCs could uniformly impregnate into the three-dimensional CA network to effectively improve its properties. The impregnation of cationic CNCs at 0.5 wt% concentration drastically increased the tensile strength (1669%) while maintaining high permeation flux of 9400 Lm-2h-1 which is remarkable with cellulose modified electrospun membranes. The membranes infused with anionic CNCs exhibited a particle retention efficiency of 96% for 500 nm and 77% for 100 nm latex beads whilst the cationic CNC membranes exhibited a combined particle retention strategy using selectivity and size exclusion with a retention of >81% with 100 nm latex beads and 80% with ∌50 nm silver nanoparticles. We envision that the developed multifunctional membranes can be utilized for affinity-based and size-exclusion filtration to selectively trap bacteria or substances of biological significance.
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