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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
171

Characterization of cellulose pulps and the influence of their properties on the process and production of viscose and cellulose ethers

Strunk, Peter January 2012 (has links)
Today’s market offers an ever-increasing range of cellulose pulps (derivative pulps) made fromvarious wood types through different delignification processes. Each pulp segment has its uniquecharacteristics, which makes it difficult for the producer of cellulose derivatives to choose the mostsuitable pulp for optimum processability and product quality. The objective of this study was toimprove knowledge of cellulose pulps and to describe how different pulp properties affectprocessability and quality in the production of viscose dope and cellulose ethers.Ten pulp samples were investigated, originating from both sulfite and sulfate processes, with highand low viscosities and with softwood and hardwood as raw material. The pulps were analyzed fortheir properties and then processed to viscose dope and a cellulose ether in two separate pilotfacilities. The intermediates in the viscose process as well as the quality of the viscose dope andcellulose ether were analyzed and the results correlated to pulp properties.Multivariate regression methods were applied to investigate the dominating physical and chemicalproperties of each pulp and pulp segment, and to study the use of spectroscopic analyses inpredicting pulp origin, concentration and composition of hemicelluloses as well as the content ofreducing end groups in cellulose. For the production of viscose dope, the models presented showedthe most important pulp properties for good cellulose reactivity and viscose filterability. In addition,the properties affecting gel formation, flocculation, degree of substitution and clarity in theproduction of cellulose ether were highlighted. The study also emphasized the need to supplementthe use of conventional analyses on pulps and viscose intermediates with other analytical methods,such as molecular weight distribution and carbohydrate analysis, to better predict the quality ofboth viscose dope and viscose fiber.The results of the present study could be useful to predict the origin and properties of new pulps, toreplace or supplement otherwise expensive pulp analyses, and to assess the impact of pulpproperties on the production of cellulose derivatives without extensive pilot-scale trials.
172

Occupational exposure to brominated flame retardants : With emphasis on polybrominated diphenyl ethers

Thuresson, Kaj January 2004 (has links)
Brominated flame retardants (BFRs) are a diverse group of chemicals, which are used to slow down or inhibit the development of fires. BFRs are incorporated into a wide range of consumer products that are considered as potential fire hazards, such as TV-sets, household appliances, computers, and textiles. The production and use of BFRs is extensive and consists of mainly tetrabromobisphenol A (TBBPA), polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecan (HBCD). BFRs in general, but in particular the PBDEs, have led to both scientific and public concern since they have been found to bioaccumulate in humans and wildlife. The general population is targeted by the PBDEs due to their applications and via the food web. Occupational exposure occurs not only during direct handling of BFRs, but also during handling, repair and dismantling of flame retarded goods. This thesis is aimed to assess occupational exposure to BFRs. It is mainly focused PBDEs and especially the PBDEs with high bromine content, such as decabromodiphenyl ether (BDE-209). The work has been accomplished by analysis of BFRs in indoor air at industries handling BFRs or flame retarded goods, and by analysis of blood drawn from workers with potential exposure to BFRs. A referent group, abattoir workers with no occupational exposure to PBDEs, was also investigated. Data from these cross-sectional investigations and from serum sampling during vacation in PBDE-exposed workers have been used for calculation of apparent halflives of hepta- to decaBDE in serum. The results clearly show that the workers were exposed to PBDEs when handling PBDE containing products or goods. The serum PBDE levels in computer technicians were found to correlate to the estimated cumulative work hours with computers. Exceptionally high concentrations of BDE-209, almost up to 300 pmol/g lipid weight (l.w.) were observed in serum from rubber workers manufacturing or handling rubber compound that was flame retarded with a technical mixture of decabromodiphenyl ether (DecaBDE). Elevated concentrations of PBDEs with eight or nine bromine substituents were also observed. In an electronics dismantling plant, where elevated levels of PBDEs previously had been observed, reduced serum levels of some, but not all PBDE congeners were observed after industrial hygiene improvements. Notably, it was observed that the BDE-209 concentrations in referents with no occupational exposure were similar to the concentrations of 2,2’,4,4’- tetrabromodiphenyl ether (BDE-47), often referred to as the most abundant PBDE congener in humans and wildlife. Additionally, PBDEs with high bromine content were found to have a fast rate of elimination or transformation in humans, based on serum analysis. BDE-209 had an apparent half-life in serum of only 15 days. The possibility of quantifying BFRs, such as PBDEs, in human serum at low levels of detection has been achieved by reducing the contamination of the samples and procedural blanks. Major efforts have been done to develop routines and clean up methodology to enable an almost contamination-free environment at the laboratory. The use of a clean room has decreased PBDE levels in the blanks to acceptable limits. The modifications of the original analytical method have made it possible to quantify almost all PBDE congeners of interest in one GC/MS run. Occupational and general background exposure of BFRs to humans will continue as long as these chemicals are a part of our daily life and present as environmental contaminants. The present scientific knowledge of the potential health risks of these BFRs still needs to be further developed. It should be stressed that health effects to PBDEs have not been assessed in this work. It is the author's wish that this thesis should add another piece of knowledge to the puzzle of BFRs and BFR exposure to humans and that these data will be used in future risk assessments of PBDEs in particular.
173

PBDEs in the Environment : Time trends, bioaccumulation and the identification of their successor, decabromodiphenyl ethane

Kierkegaard, Amelie January 2007 (has links)
Polybrominated diphenyl ethers (PBDEs) are important chemical flame retardants, but also environmental pollutants. Their bromine substitution lends them a different bioaccumulation behaviour than the better studied organochlorines. The contamination of a Swedish lake with lower brominated BDEs was assessed by a retrospective study of pike. The concentrations of tetra- to hexaBDEs increased exponentially up to the mid-1980s and then decreased slowly, possibly reflecting the voluntary reduction in production/usage of the chemicals. Methoxylated PBDEs were found to be present in similar concentrations to the PBDEs, but originated from different sources. The large size of the bromine atom was believed to result in negligible absorption of higher brominated BDEs in wildlife, thus explaining the low levels observed in fish despite high levels in e.g. sediment. However, it was shown that the fully brominated BDE, BDE209, was absorbed to a small extent via the diet. Once absorbed, it was reductively debrominated to lower brominated BDE congeners. Debromination was also observed in dairy cows exposed to higher brominated BDEs in their natural diet. Moreover, the molecular size restricted the transfer of higher brominated BDEs to milk. In contrast to PCBs and lower brominated BDEs, there was no equilibrium between adipose tissues and milk fat, and with increasing bromine substitution a progressively smaller fraction of the ingested PBDEs was transferred to the milk. This thesis highlights differences in uptake, metabolism and excretion for PBDEs compared to the well characterized organochlorines. A knowledge that is useful for risk assessments given the ongoing use of these compounds. Furthermore, a representative of the next generation brominated flame retardants, decabromodiphenyl ethane, a replacement for the BDE209 technical product, was identified for the first time in the environment.
174

Heck Reactions with Aryl Chlorides : Studies of Regio- and Stereoselectivity

Datta, Gopal K. January 2008 (has links)
Homogeneous palladium-catalyzed Heck vinylation of aryl chlorides was investigated under air using Herrmann’s palladacycle and the P(t-Bu)3-liberating salt [(t-Bu)3PH]BF4. Based on the results, controlled microwave heating was utilized to accelerate model Heck reactions with aryl chlorides down to 30 min employing an electron-poor olefin and a mixture of an ionic liquid and 1,4-dioxane as solvent. For the first time, a highly regioselective general protocol has been developed for palladium-catalyzed terminal (β-) arylation of acyclic vinyl ethers using inexpensive aryl chlorides as starting materials and the preligand [(t-Bu)3PH]BF4 as the key additive. This swift and straightforward protocol exploits non-inert conditions and controlled microwave heating to reduce handling and processing times, and aqueous DMF or environmentally friendly PEG-200 as the reaction medium. Somewhat higher selectivity for the linear β-product was observed in PEG-200. DFT calculations were performed at the B3LYP level of theory for the regioselectivity-determining insertion step in the Heck reaction following the neutral pathway. A series of para-substituted phenylpalladium(II) complexes was investigated in the computational study. The calculations support a ligand-driven selectivity rationale, where the electronic and steric influence of the bulky P(t-Bu)3 ligand provides improved β-selectivity. The preparative methodology was used to synthesize the β-adrenergic blocking agent Betaxolol. Highly stereoselective Pd(0)-catalyzed β-arylation and β-vinylation of a tetra-substituted cyclopentenyl ether have been accomplished using a chiral, pyrrolidine-based and substrate-bound palladium(II)-directing group under neutral reaction conditions. To the best of the author’s knowledge, this P(t-Bu)3-mediated method represents the first examples of the successful utilization of aryl and vinyl chlorides in asymmetric Heck reactions. The Heck arylation products formed were hydrolyzed and isolated as the corresponding quaternary 2-aryl-2-methyl cyclopentanones in good to moderate two-step yields with excellent stereoselectivity (90-96% ee). Inclusion of vinyl triflates under neutral reaction conditions and one aryl triflate equipped with a strongly electron-withdrawing para-cyano substituent under cationic conditions increased the preparative usefulness of the methodology. Furthermore, diastereoselective Heck arylation of both five- and six-membered cyclic vinyl ethers with aryl bromides, using the identical chiral auxiliary and suitable Pd sources, was performed. Arylated products from the tetra-substituted cyclopentenyl ether were also in this case hydrolyzed to the corresponding 2-aryl-2-methyl cyclopentanones with high to excellent enantioselectivity (85-94% ee). Despite low reaction rates and relatively modest yields, arylation reactions with the tri-substituted cyclohexenyl ether were found to be highly diastereoselective (94-98% de). Thus, an attractive supplement to direct Pd(0)-catalyzed α-arylation protocols, particularly when the use of organic chlorides, aryl bromides, and milder reaction conditions are of great importance, have been developed.
175

Physical and Electro-Optical Characterization and Application of Novel Poly(arylene ether)s with High Tg¡¦s

Tsao, Tzu-i 27 July 2007 (has links)
There are three novel 2-trifluoromethyl-activated bisfluoro monomers have been successfully synthesized in this study, and the nomenclatures are shown as follows: 4,4¡¦¡¦¡¦¡¦-Difluore-3,3¡¦¡¦¡¦¡¦-bis(trifluoromethyl)-2¡¦¡¦,3¡¦¡¦,5¡¦¡¦,6¡¦¡¦-triphenyl(M4), 4,4¡¦¡¦¡¦¡¦-Difluore-3,3¡¦¡¦¡¦¡¦-bis(trifluoromethyl)-2¡¦¡¦,3¡¦¡¦,5¡¦¡¦-triphenyl(M3), 4,4¡¦¡¦¡¦¡¦-Difluore-3,3¡¦¡¦¡¦¡¦-bis(trifluoromethyl)-2¡¦¡¦,3¡¦¡¦-triphenyl(M2). Through polymerization with 1,1-dihydroxydiphenyl cyclododecane the monomers M2, M3 and M4 were accordingly converted into poly(arylene ether)s P2-1,1C, P3-1,1C and P4-1,1C, respectively. These polymers exhibit weight-average molecular weight up to 2.25¡Ñ105g/mol. The molecular weight were investigated and confirmed by MASS and GPC. The molecular structures were investigated and confirmed by NMR and FTIR. The UV-VIS absorption and photoluminescence spectra measurement of all the monomers and polymers in dilute solutions and in solid state were conducted. The results show that all monomers and polymers in dilute solutions have no absorption in the vision light region of spectrum. The absorption spectra of polymer thin films showed high optical transparency up to 90%. The photoluminescence spectra of all monomers and polymers in dilute solutions and thin film emits light with high intensity and wavelength in region of 350~380nm. Thermal analysis studies were conducted with TGA, DSC, TMA and crystal property study was performed by XRD. The results show that these polymers did not show melting but showed ultrahigh Tg values ranging from 270~330¢XC in DSC and TMA measurements, so it indicated that three polymers were not crystalline materials. Outstanding thermal stability is over then 440~ 460¢XC for 5% weight loss in TGA under nitrogen atmosphere. So it could make manufacture in higher temperature and have higher thermal stability. With optical properties of polymer thin films, we utilized Ellipsometer to measure refractive index and the results showed no birefringence for these polymers. The polymer thin films show low polarity and high hydrophobicity could be attested by the measured results of contact angle and surface energy. The HOMO and LUMO energy level of monomers are both measured by Cyclic Voltammetry and theoretical calculation. The absorption spectra of polymer thin films showed no absorption in the visible light region of the spectrum i.e., having a high optical transparency. All above stated material properties are good for doing as a plastic substrate of devices or panel display.
176

Fabrication of polymeric microfluidic devices via photocurable liquid monomers

Haraldsson, Klas Tommy January 2005 (has links)
Microfluidic devices have long been considered an ideal tool for rapid and inexpensive chemical analysis and reactions in areas ranging from point-of-care health to national security applications. However, fabricating microfluidic devices is time consuming, difficult and above all expensive. In commercial applications many thousand units need to be sold before the development costs are recovered. The problem is compounded since most microfluidic devices do not have generalized architectures which means that each end use requires a specialized design. The microfluidics marketplace can therefore be seen as being composed of 1000’s of niche markets. To address development costs, there is clearly a need for a versatile technology that can be used for many different applications and that enables rapid testing and optimization of new designs. This work describes such a technology: Contact Liquid Photolithographic Polymerization (CLiPP). The thesis consists of two parts: polymerization kinetics and the fabrication of polymeric microfluidic devices via CLiPP. The photopolymerization kinetics is evaluated for a number of monomer types, and the results are used to assess their suitability in the CLiPP process. Vinyl ether/maleate photoinitiated copolymerization is examined in detail. It is shown that the polymerization kinetics is dramatically influenced by the availability of easily abstractable hydrogens The presence of α-hydrogens adjacent to the vinyl ether functional group reduces the polymerization rate and the dependence of the polymerization rate as a function of initiation rate. Also, photoinitiated acrylate and methacrylate polymerization kinetics are presented. The kinetics results in these three monomer types are used to explain the different patterning properties of the monomer functionalities used in the CLiPP process, in which acrylates show enhanced patterning properties compared to methacrylates. The polymerization kinetics is studied with traditional tools and methods: photo Differential Scanning Calorimetry (photo-DSC), photo Fourier Transform Real Time Infrared Spectroscopy (photo-RTIR), and photo Real Time Electron Paramagnetic Spectroscopy (ESR). The microfluidic fabrication is performed via both in-house fabricated and commercially available CLiPP-specific hardware. The patterning qualities of the structures are evaluated via Scanning Electron Microscopy (SEM) and Optical Microscopy. The finished devices are used in their intended environment and evaluated in suitable manners to assess their utility. In this thesis, the development and design of specialized CLiPP fabrication machines, fabrication techniques and resulting microfluidic device features are presented anddiscussed. It is shown that the CLiPP scheme enables features such as 3 dimensional (3D) capabilities for minimized device footprints, a very large number of polymeric materials for optimized device components as well as facile integration of prefabricated components. Also, covalent layer adhesion and permanent surface modifications via living radical processes are demonstrated. These capabilities are exemplified in a number of examples that range from a 3D fluidic channel maze with separated fluidic streams and a device with independently moveable parts to a device constructed from multiple polymeric materials and devices with permanently modified surfaces, Also, batch processing capabilities are shown through fabrication of 400 identical undercut microstructures. Rapid and inexpensive design evaluations, multiple materials capabilities and the ability to seamlessly incorporate prefabricated microstructures of the CLiPP process strongly encourages continued method development. The future work that remains to be addressed is divided into two parts. First, to enable novel research devices, new polymer materials with enhanced mechanical and surface properties must be developed. Also, integration of prefabricated microstructures such as sensors and actuators has to be incorporated in a reproducible and rational manner. Secondly, to enable device mass fabrication, new automated equipment is to be developed in order to utilize the full batch processing potential of CLiPP. / QC 20101019
177

Excess molar enthalpies of binary and ternary systems involving hydrocarbons and ethers

Hasan, S. M. Nazmul 14 January 2011
In modern separation design, an important part of many phase-equilibrium calculations is the mathematical representation of pure-component and mixture enthalpies. Mixture enthalpy data are important not only for determination of heat loads, but also for the design of distillation units. Further, mixture enthalpy data, when available, are useful for extending vapor-liquid equilibria to higher (or lower) temperatures, through the use of the Gibbs-Helmholtz equation. In this connection excess molar enthalpies for several binary and ternary mixtures involving ethers and hydrocarbons have been measured at the temperature 298.15 K and atmospheric pressure, over the whole mole fraction range. Values of the excess molar enthalpies were measured by means of a modified flow microcalorimeter (LKB 10700-1) and the systems show endothermic behavior. The Redlich-Kister equation has been used to correlate experimental excess molar enthalpy data of binary mixtures. Smooth representations of the excess molar enthalpy values of ternary mixtures are accomplished by means of the Tsao-Smith equation with an added ternary contribution term and are used to construct excess enthalpy contours on Roozeboom diagrams. The values of the standard deviations indicate good agreement between experimental results and those calculated from the smoothing equations. The experimental excess enthalpy data are also correlated and predicted by means of solution theories (Flory theory and Liebermann-Fried model) for binary and ternary mixtures, respectively. These solution theories correlate the binary heats of mixing data with reasonable accuracy. The prediction of ternary excess molar enthalpy by means of the solution theories are also presented on Roozeboom diagrams. The predictions of ternary excess enthalpy data by means of these theories are reasonably reliable.
178

Excess molar enthalpies of binary and ternary systems involving hydrocarbons and ethers

Hasan, S. M. Nazmul 14 January 2011 (has links)
In modern separation design, an important part of many phase-equilibrium calculations is the mathematical representation of pure-component and mixture enthalpies. Mixture enthalpy data are important not only for determination of heat loads, but also for the design of distillation units. Further, mixture enthalpy data, when available, are useful for extending vapor-liquid equilibria to higher (or lower) temperatures, through the use of the Gibbs-Helmholtz equation. In this connection excess molar enthalpies for several binary and ternary mixtures involving ethers and hydrocarbons have been measured at the temperature 298.15 K and atmospheric pressure, over the whole mole fraction range. Values of the excess molar enthalpies were measured by means of a modified flow microcalorimeter (LKB 10700-1) and the systems show endothermic behavior. The Redlich-Kister equation has been used to correlate experimental excess molar enthalpy data of binary mixtures. Smooth representations of the excess molar enthalpy values of ternary mixtures are accomplished by means of the Tsao-Smith equation with an added ternary contribution term and are used to construct excess enthalpy contours on Roozeboom diagrams. The values of the standard deviations indicate good agreement between experimental results and those calculated from the smoothing equations. The experimental excess enthalpy data are also correlated and predicted by means of solution theories (Flory theory and Liebermann-Fried model) for binary and ternary mixtures, respectively. These solution theories correlate the binary heats of mixing data with reasonable accuracy. The prediction of ternary excess molar enthalpy by means of the solution theories are also presented on Roozeboom diagrams. The predictions of ternary excess enthalpy data by means of these theories are reasonably reliable.
179

Application of Organic Optoelectronic Materials and Flexible Electronics

Lee, Chun-Che 14 December 2010 (has links)
We proposed a flexible electronics with functional poly (arylene ether)s and discotic liquid crystal. Firstly, we provided a series of the PAE polymer with remarkable thermal stability and high optical transmittance. The PAEs were synthesized via nucleophilic displacement as polymerization on a 2-trifluoromethyl-activated bisfluoro monomer, which reacted with bisphenols. Thermal analysis indicated the PAEs possessed a high glass transition point of ~300¢J and the decomposition temperature Td=500¢J at a weight loss of 5%. Additionally, high transmittance of 85%, low dielectric constant of ~2.0, and well mechanical property of the PAE films were experimentally verified, as a high potential substrate for flexible electronics. Two kind of device structure has been prepared, were organic thin film solar cell and Dye sensitized solar cell. Furthermore, we provided the self-assembled triphenylene-based liquid crystal and its polymer derivative to apply for photovoltics. The 2, 3, 6, 7-tetra-6-octyloxydibenzo[a,c]phenazine-11-carboxylic group and the polymer of merging with disc-unit and polyacrylamide. Both show a highly isotropic phase transition point of ~270¢J and the decomposition temperature Td~450¢J at a weight loss of 5%. The specific absorption in visible light region was at 200 - 450 nm. A distinct self-arrangement of columnar array was investigated by optical textures. The self-arranged pathway enhanced carrier mobility due to £k-£k conjugation in hexagonal column stacking. Finally, the PAEs and DLC materials applied to thin film solar cell (ITO/PEDOT:PSS/DLC-PAM/P3HT:PCBM/Al) as hole transporting layer. The photo-conversion efficiency was strong depending on organic compounds, such as molecular structure, photo-physic and chemical properties. On the basis of integrated characteristics, it suggested a high potential as flexible electronics for photovoltics.
180

Synthesis Of Novel Blue-emitting Poly(arylene ether)s with Application to Light Emitting Diodes

Chang, Ming-sian 19 July 2012 (has links)
In this thesis, a novel blue Poly (arylene ether) s polymer was prepared for the organic polymer light emitting diodes which was composed of the main material anthracene difluoro monomer derivatives, and object material of triphenylamine with the extension structure similar to the literature seen BD-1 asymmetric derivatives, as the hole transport material of carbazole of the diol derivatives. In general, Anthracene derivatives and BD-1, often seen in the literature as the host, guest blue polymer doping, the main use to Forster energy transfer to transfer energy to the guest, so it has good luminous efficiency. Anthracene, flat Good, easy to crystallization during evaporation, resulting in leakage generated; and the deposition of the multilayer structure will hinder charge injection to the emitting layer. From the angle of the molecular design of this study. (1) Use of the CF bond and Carbazole increase the steric hindrance of the polymer chain and change by fluoride compounds of the highest occupied molecular orbital - lowest unoccupied molecular orbital energy level. (2) The hole transport layer to import into the emitting layer. The two monomers Anthracene derivatives fluoride monomer the Carbazole of diol derivatives via nucleophilic polycondensation synthesis of a novel in proper proportion, Blue polymer. Component parts, the Blue poly aromatic ether polymer doped with a small amount of blue light-emitting guest as a component layer of the component structure: ITO / PEDOT: PSS / emitting layer / LiF / Al light-emitting layer can make use of spin coating of solvent process, and its advantage is the convenience of the process and a large area. The undoped guest before the Blue polymer production the PLED starting voltage can be reduced to 4.5 V, and maximum brightness 7 466 cd/m2, efficiency as high as 4.2 cd / A. C.I.E. coordinates of (0.15,0.08), very close to the official regulations of the NTSC Blue coordinates (0.14,0.08). When doped with 3% of the guest, the starting voltage can be reduced to 4.5 V, maximum brightness of 12104 cd/m2 and efficiency as high as 5.79 cd/A.

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