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- Eivazihollagh, Alireza
(författare)
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Metal-Chelate Complexes in Alkaline Solution : On Recovery Techniques and Cellulose-based Hybrid Material Synthesis
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For decades, aminopolycarboxylate chelating agents have been extensively used in various industrial applications. The ability of chelating agents to form stable metal-chelate complexes is the main reason for using them to manage metal ions within water-based industrial processes. Considerable quantities of industrial effluent containing chelating agents and heavy metals are produced and often discharged into the environment. The toxicity of heavy metals and the non-biodegradability of the chelating agents, as well as their accumulation in the environment, has become cause for concern. The main purpose of this thesis was to evaluate and develop processes for recovery of chelated metal complexes from aqueous solution. In this regard, the membrane electrolysis technique was evaluated for recovery of copper and aminopolycarboxylic chelating ligands such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), and a surface-active derivative of DTPA, 2-dodecyldiethylenetriaminepentaacetic acid (C12-DTPA) from aqueous solution. By using this method, it was possible to simultaneously recover the chelating ligand for further reuse and collect the metals by electrodeposition, making the process more cost-effective and hindering the discharge of copper ions and chelating ligands as pollutants into the environment. In addition, the ion flotation technique with the chelating surfactant C12-DTPA could be employed to separate metal ions, especially from their dilute solutions, and concentrate them in a foam phase. This is because C12-DTPA has a purpose-built functionality; besides forming strong coordination complexes with metal ions, it is also surface-active and will readily adsorb at air-water interfaces. In this study, C12-DTPA was effectively used in combination with foaming agents for the removal of toxic metal ions such as Cd2+, Zn2+, and Sr2+ from aqueous solution using ion flotation. From an economical perspective, this method could be combined with the membrane electrolysis technique to recover metal and regenerate chelating surfactant so that it can be reused.The present work also shows the synthesis of metal and metal oxide(s) nanoparticles (NPs) in alkaline aqueous solution containing chelated metal ions, in order to fabricate metal NPs–cellulose hybrid materials. Cellulose is the most abundant renewable material, with good mechanical performance and chemical resistivity in a wide range of solvents, which makes it a promising material to support metal NPs. In this respect, we developed a rapid and inexpensive one-pot synthesis of spherical copper NPs in a cellulose matrix. The hybrid material displayed antibacterial properties for both the gram-negative and gram-positive bacteria. The synthesis was further developed by studying the influence of various chelating ligands and surfactants on the NPs’ morphology and chemical composition. According to the results, DDAO, a zwitterionic surfactant, was found to mediate the formation of pure octahedral Cu2O NPs. In addition, a hybrid material film composed of regenerated cellulose and synthesized Cu2O nano-octahedrons was fabricated by spin-coating.
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| 2. |
- Halvarsson, Sören, 1956-
(författare)
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Manufacture of straw MDF and fibreboards
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this thesis was to develop an economical, sustainable, and environmentally friendly straw Medium Density Fibreboard (MDF) process, capable of full-scale manufacturing and to produce MDF of requested quality. The investigated straw was based on wheat (Triticum aestivum L.) and rice (Oryzae sativa L.). In this thesis three different methods were taken for manufacture of straw MDF; (A) wheat-straw fibre was blowline blended with melamine-modified urea-formaldehyde (MUF), (B) rice-straw fibre was mixed with methylene diphenyl diisocyanate (MDI) in a resin drum-blender, and (C) wheat-straw fibre was activated in the blowline by the addition of Fenton’s reagent (H2O2/Fe2+) for production of non-resin MDF panels. The MUF/wheat straw MDF panels were approved according to the requirements of the EN standard for MDF (EN 622-5, 2006). The MDI/rice-straw MDF panels were approved according to requirements of the standard for MDF of the American National Standard Institute (ANSI A208.2-2002). The non-resin wheat-straw panels showed mediocre MDF panel properties and were not approved according to the requirements in the MDF standard. The dry process for wood-based MDF was modified for production of straw MDF. The straw MDF process was divided into seven main process steps. 1. Size-reduction (hammer-milling) and screening of straw 2. Wetting and heating of straw 3. Defibration 4. Resination of straw fibre 5. Mat forming 6. Pre-pressing 7. Hot-pressing The primary results were that the straw MDF process was capable of providing satisfactory straw MDF panels based on different types of straw species and adhesives. Moreover, the straw MDF process was performed in pilot-plant scale and demonstrated as a suitable method for producing straw MDF from straw bales to finished straw MDF panels. In the environmental perspective the agricultural straw-waste is a suitable source for producing MDF to avoid open field burning and to capture carbon dioxide (CO2), the biological sink for extended time into MDF panels, instead of converting straw directly into bio energy or applying straw fibre a few times as recycled paper. Additionally, the straw MDF panels can be recycled or converted to energy after utilization. A relationship between water retention value (WRV) of resinated straw fibres, the thickness swelling of corresponding straw MDF panels, and the amount of applied adhesive was determined. WRV of the straw fibre increased and the TS of straw MDF declined as a function of the resin content. The empirical models developed were of acceptable significance and the R2 values were 0.69 (WRV) and 0.75 (TS), respectively. Reduced thickness swelling of MDF as the resin content is increased is well-known. The increase of WRV as a function of added polymers is not completely established within the science of fibre swelling. Fortunately, more fundamental research can be initiated and likely a simple method for prediction of thickness swelling of MDF by analysis of the dried and resinated MDF fibres is possible.
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| 5. |
- Costa, Carolina
(författare)
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Cellulose Dissolution and Amphiphilicity : Insights on the Emulsion Formation and Stabilization
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An amphiphilic polymer is expected to adsorb at the oil-water interface and be capable of stabilizing emulsions. Cellulose derivatives, cellulose nanoparticles and regenerated cellulose particles show an intrinsic amphiphilic character by self-assembling at oil-water interfaces and stabilizing emulsions without the aid of surfactants or any other co-stabilizers. In its polymeric form, the native cellulose chains could be expected to share similar emulsifying abilities. However, cellulose dissolution is the main issue when it comes to its direct application in emulsion technology and, therefore, there is a lack of knowledge when it comes to this type of approach on making emulsions. Cellulose does not dissolve in either oil or water, but it can be dissolved in water based-solvents at extreme pH's. In this thesis, the interfacial behaviour of cellulose was studied at oil-water interfaces by having cellulose dissolved in aqueous solutions of H3PO4 (very low pH) and NaOH/NaOH-urea and TBAH (very high pH). In its dissolved state, cellulose was seen to substantially decrease the interfacial tension (IFT) between the oil phase and the aqueous media, which was a consequence of the adsorption of cellulose at oil-water interfaces. The extent of the IFT reduction was shown to be dependent on the solvent quality. The optimal solvency conditions for cellulose were found for the alkaline solvent with an intermediate polarity (NaOH-urea), which is in line with the favourable conditions for adsorption of an amphiphilic polymer. However, in stabilizing oil-in-water emulsions (O/W), to achieve long-term stability and prevent oil separation from the emulsions, further reduction in cellulose's solvency was needed. This was achieved by a change in the pH of the emulsions that induced the regeneration of cellulose on the surface of the oil droplets (in-situ regeneration) in the form of a continuous film, which was revealed by cryogenic scanning electron microscopy (cryo-SEM). The topography of the droplets surface was found to be very different from what has been reported for cellulose Pickering emulsions. Upon in-situ regeneration, the rate of droplets coalescence was dramatically reduced and emulsions showed a remarkable stability against oil-separation. Finally, the combination of cellulose with lignin as an amphiphilic natural co-stabilizer was studied regarding their compatibility in solution. Lignin was found to improve cellulose dissolution in NaOH (aq.) and delay the gelation kinetics upon ageing or temperature increase in the solutions. Data suggests lignin as an amphiphilic additive able to weaken the hydrophobic interactions among cellulose molecules.
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| 6. |
- Yang, Jiayi
(författare)
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Utilization of cellulosic biomass towards sustainable chemicals and novel biomaterials
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is predicted by the United Nations that by year 2030 the world will need at least 50 percent more food, 45 percent more energy and 30 percent more water. The emissions of carbon dioxide from combustion of fossil fuels and waste are also increasing. At the same time, the demand for natural resources has never been higher and the planet is under unprecedented stress. This increasing awareness and concerns also drive and accelerate the research to facilitate switching the fossil-dependent economy to biobased economy. In this premise, forest industry plays a significant role, from leading the sustainable development to providing more materials to meeting the expanding demand. Moreover, the forest industry is a crucial part of the solution to global warming. The utilization of forest product has a long history, and the efforts of converting the biomass into value-added products or innovative applications have never been more stimulated than now. This thesis presents some examples of the exploration of lignocellulosic biomass based on the fractionation of lipophilic extractives and utilization of non-derivatized cellulose in novel materials.In the first part of thesis, the biorefinery of thermo-mechanical pulping (TMP) process water for lipophilic extractives was investigated as a way to extract the dissolved and colloidal substance (DCS). It was found that induced air flotation (IAF) combined with the foaming agent dodecyl trimethylammonium chloride (DoTAC) can efficiently remove the unwanted lipophilic extractives (Paper I) and retain valuable hemicelluloses (Paper II) in the TMP process water. By applying 80 ppm of DoTAC at a pH of 3.5 and 50 °C with induced air flotation, 94% of the lipophilic extractives were refined from the process water. The efficient biorefining of lipophilic extractives not only enabled the purification of TMP process water, but also facilitate the selective harvesting of hemicelluloses with very low impurities.In the second part of the work, non-derivatized cellulose (sulfite pulp) dissolved in LiOH/urea was used as substrate to fabricate spherical nanocomposite particles (Paper III), pH-responsive nanocomposite films (Paper IV) and crosslinked cellulose hydrogel (Paper V), respectively. The cellulose-chitosan nanocomposite particles were prepared in three different ways: instantly by dripping alkaline cellulose solution into dissolved chitosan in diluted acetic acid, and by mixing and emulsifying the biopolymer solutions to a water-in-oil emulsion, with or without addition of a crosslinking agent. Spherical cellulose-chitosan nanocomposite particles in the size from millimeter to micrometers were successfully prepared. It was demonstrated that some properties of the spherical particles, for example, morphology and size distribution, could be tuned by choosing between the different routes of preparation. In a different application of LiOH/urea dissolved cellulose, in the form of cellulose-chitosan nanocomposite films with pH-responsive swelling, were shown in the thesis. The nanocomposite film with 75% chitosan content exhibited maximum swelling ratio of 1500% and weight loss of chitosan of 55 wt% after 12 hours at pH 3. The utilization of the non-derivatized cellulose continued with cross-linking the macromolecules with methylenebisacrylamide (MBA) to form a robust hydrogel with superior water absorption properties. The cellulose hydrogel cured at 60 °C for 30 minutes, with a [MBA]/[glucose] molar ratio of 1.05, exhibited the highest water swelling capacity absorbing ca. 220 g H2O/g dry weight. This innovative procedure based on the direct dissolution of unmodified cellulose in LiOH/urea followed by MBA cross-linking provides a simple and fast approach to prepare chemically cross-linked cellulose hydrogels of high molecular weight with superior water uptake capacity.
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