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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.
41

Emulsion copolymerization with functional monomers in continuous reactors

Lange, David M. 05 1900 (has links)
No description available.
42

Continuous miniemulsion polymerization

Barnette, Darrell Thomas 12 1900 (has links)
No description available.
43

Effects of Cyclodextrins on the Kinetics of Emulsion Polymerisation

El-Hadad, Omar January 2009 (has links)
Cyclodextrins (CD) are semi-natural oligosaccharides composed of a number of D-glucose units. They are produced from renewable resources, and have been found to be of catalytic effect for the emulsion polymerization of many monomers. Using monomers whose emulsion polymerization kinetics have been thoroughly studied, this research analyses the effect of CD on the entry and exit rate coefficients for the emulsion polymerization of styrene, and the entry and termination rate coefficients for the emulsion polymerization of MMA. Throughout the course of the work, CD was found to have a positive impact on the polymerization rate of styrene in a polystyrene latex stabilized with a cationic surfactant. Furthermore, the exit rate coefficient for this latex was found, via γ-relaxation experiments, to increase in proportion to the styrene solubility in water, exactly as predicted by theory. Of itself this would lead to a decrease in reaction rate. That there is still an overall increase in the reaction rate in the presence of CD is because of a quite strong effect on entry rate coefficients. Again, this is consistent with the prevailing theory for entry, that of Maxwell and Morrison, which says that increased aqueous phase solubility of monomer will lead to faster entry. Intriguingly, experiments done on a polystyrene latex stabilized with an anionic surfactant showed a different effect for CD: γ-relaxation experiments found very little effect of CD on exit rate, and chemically initiated experiments found the same for overall rate. This is consistent with CD having little effect on aqueous phase styrene solubility, which in fact is what direct measurements via UV-visible spectroscopy indicated. It is speculated that the anionic surfactant was successfully competing with styrene to occupy the CD cavities. On the other hand, measurements suggested that styrene successfully competes with cationic surfactant, which is consistent with kinetic results. Experiments of the above nature were then carried out with methyl methacrylate (MMA), a more water soluble monomer than styrene and one with emulsion polymerisation kinetics of a different nature (so-called pseudo-bulk). γ-relaxation experiments found no effect of CD on termination rate coefficients, exactly as one would expect given that termination is an intra-particle reaction whereas CD exists in the aqueous phase. However the same experiments also revealed an unexpected effect of CD on entry: the thermal entry rate coefficient was found to increase markedly in the presence of CD. It seems likely that this unusual effect stems from interaction of products of γ radiolysis with CD. Results for chemically-initiated polymerization of MMA were inconclusive. Under some conditions there was actually retardation in the presence of CD, which is actually consistent with measurements of MMA solubility in water, which suggested a slightly negative effect of CD. However it is hard to explain such a phenomenon. Further, under other conditions it was found that CD either had no effect on chemically-initiated rate or could even increase it slightly. The only safe conclusion at this stage is that CD has no major effect on MMA kinetics, which arguably is consistent with MMA being relatively water soluble: intuitively one would expect that CD is most useful (‘catalytic’) for the EP of monomers of low solubility.
44

Block copolymers of poly(ethylene oxide) and poly(methyl methacrylate)

Redford, K. January 1991 (has links)
A series of five AB block copolymers of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) has been synthesised by the coupling of mono-functional homopolymers by an esterification reaction. In this series polymers all contain a PMMA component of number average molecular weight 908 gmo1·1, as measured by end group analysis, and the PEO components have number average molecular weights of 596, 689, 979, 2023 and 2884 gmol·1, as measured by proton nuclear magnetic resonance spectroscopy. Aqueous "solutions" of these copolymers have been prepared both by direct mixing and via methanol, a solvent for both blocks of the copolymer. Cloud points for these copolymers have been determined and range from 275K to 368K for the lowest and highest PEO blocks respectively. Small angle X-ray scattering (SAXS) of aqueous solutions has been interpreted in terms of a core - shell model and dimensions determined for both. Radii of gyration for the micellar cores have been shown to vary very little with variations in copolymer composition, concentration and temperature up to the cloud point. Fringe thicknesses show a dependence on PEO block length and relating measured fringe thicknesses to calculated chain conformations indicates that the the chain conformation is best described as an unperturbed chain. The measured fringe thickness is not altered by concentration or temperature up to the cloud point. Above the cloud point it is not possible to interpret the SAXS data in terms of a core shell micellar model. Significant differences in the SAXS data have been observed depending upon the mode of addition of copolymer to water. This can be interpreted as differences in micellar II structure With the exception of the lowest molecular weight copolymer all of the copolymers could be used as steric stabilisers for the aqueous emulsion polymerisation of methyl methacrylate. Polymerisations were only successful if the copolymer was introduced to the aqueous phase either via methanol or via the monomer. Direct addition of copolymer to water resulted in low polymerisation rates and unstable/flocculated products. Emulsions produced have been shown to be stable at pH levels where the electrophoretic mobility was zero, ie. the emulsions were sterically stabilised with no contribution from ionic I dipole interactions.
45

ADVANCED MODELLING OF EMULSION TERPOLYMERISATION FOR ONLINE OPTIMISATION AND CONTROL

Srour, Mourtada H January 2008 (has links)
Doctor of Philosophy(PhD) / Polymer manufacturing is a major worldwide industry, attracting the attention of numerous industrial units and research institutes. Increasing demands on polymer quality, process safety and cost reduction are the main reasons for growing interest in the design and control of emulsion polymerisation. Emulsion polymerisation process implemented with free radical polymerisation has significant advantages over other processes, such as the production of polymer of higher molecular weights at high conversion rates, easier temperature control due to the low viscosity of the reaction media, high degree of selectivity and more friendly to environment due to the use of an aqueous medium. It allows for the production of particles with specially-tailored properties, including size, composition, morphology, and molecular weights. Introducing two or more different monomers to the polymerisation process (named multi-polymerisation) can lead to the synthesis of an almost unlimited number of new polymers types. Emulsion polymers are products by process, meaning that the manner in which the polymerisation is carried out is perhaps more important than the raw materials in determining the form of the final product. This highlights the significance of the systematic approach in online process control which requires thorough understanding of the process phenomena as a prerequisite for development of a mathematical description of the process as the model. It is thus evident and based on research observations that process control for emulsion terpolymerisation is a particularly difficult task because of the lack of validated models and the lack of online measurements of most of polymer properties of interest. Therefore, a well validated model is crucial for optimising and controlling the emulsion terpolymerisation operations allowing for design of the polymer product properties. In this study, a framework for process design and control of emulsion terpolymerisation reactors was developed. This framework consisted of three consecutive stages, dynamic modelling of the process, optimising the process for finding the optimal operating strategies and final online controlling the obtained optimal trajectories through multivariable constrained model predictive control. Within this framework, a comprehensive dynamic model was developed. Then a test case of emulsion terpolymerisation of styrene, methyl methacrylate and methyl acrylate was investigated on state of the art facilities for predicting, optimising and control end-use product properties including global and individual conversions, terpolymer composition, the average particle diameter and concentration, glass transition temperature, molecular weight distribution, the number- and weight-average molecular weights and particle size distribution. The resulting model was then exploited to understand emulsion terpolymerisation behavior and to undertake model-based optimization to readily develop optimal feeding recipes. The model equations include diffusion-controlled kinetics at high monomer conversions, where transition from a ‘zero-one’ to a ‘pseudo-bulk’ regime occurs. Transport equations are used to describe the system transients for batch and semi-batch processes. The particle evolution is described by population balance equations which comprise of a set of integro-partial differential and nonlinear algebraic equations. Backward finite difference approximation method is used to discretise the population equation and convert them from partial differential equations to ordinary differential equations. The model equations were solved using the advanced simulation environment of the gPROMS package. The dynamic model was then used to determine optimal control policies for emulsion terpolymerisation in a semi-batch reactor using the multiobjective dynamic optimisation method. The approach used allows the implementation of constrained optimisation procedures for systems described by complex mathematical models describing the operation of emulsion terpolymerisation reactors. The control vector parameterisation approach was adopted in this work. Styrene monomer feed rate, MMA monomer feed rate, MA monomer feed rate, surfactant feed rate, initiator feed rate and the temperature of reactor were used as the manipulating variables to produce terpolymers of desired composition, molecular weight distribution (MWD) and particle size distribution (PSD). The particle size polydispersity index (PSPI), molecular weight polydispersity index (MWPI) and the overall terpolymer composition ratios were incorporated as the objective functions to optimise the PSD, MWD and terpolymer composition, respectively. The optimised operational policies were successively validated with experiments via one stirred tank polymerisation reactor. Due to the lack of online measurements of key process product attributes for emulsion terpolymerisation, an inferential calorimetric soft sensor was developed based on temperature measurements. The calorimetric soft sensor obtains online measurements of reactor temperature, jacket inlet and outlet temperatures helped estimate the rate of polymerisation. The model includes the mass and energy balance equations over the reactor and its peripherals. Energy balance equations include the heat of reaction, internal and external heat transfer effects, as well as external heat losses. An online multivariable constrained model predictive control was formulated and implemented for online control of the emulsion terpolymerisation process. To achieve this implementation, a novel generic multilayer control architecture for real-time implementation of optimal control policies for particulate processes was developed. This strategy implements the dynamic model for the emulsion terpolymerisation as a real-time soft sensor which is incorporated within the implemented MPC. The methodology was successively validated using six case studies within the on-line control of terpolymerisation reactors. The cases were online controlled the composition of terpolymers, PSD and Mn with specific constraints for the operation conversion and particle average radius. An advanced Supervisory Control Architecture named ROBAS was used in this work. It provides a completely automated architecture allowing for the real time advanced supervisory monitoring and control of complex systems. The real time control application strategy was developed within MATLAB, Simulink, gPROMS and Excel Microsoft softwares and implemented on line through ROBAS Architecture. The manipulated variables are measured using on-line measurements connected to the DCS system through Honeywell. These measurements were sent to MATLAB and then to the dynamic model in gPROMS through an excel spread-sheet interface. Then the dynamic model used them to estimate the controlled variables of the MPC. The estimated values of the controlled variables obtained from the dynamic model, were then sent to the Simulink and fed through the DCS system to the MPC developed in MATLAB. The MPC would then calculate optimal trajectories, which are then sent as set point signals through the DCS system to the regulatory controller. The MPC formulation was found to be robust and handles disturbances to the process. The result showed that the online multivariable constrained MPC controller was able to control the desired composition and Mn as specified set points with great accuracy. The MPC algorithm succeeded under constrained conditions, in driving the PSD to the desired target. Although some offset was observed with a certain degree of model mismatch, the experimental results agreed well with predictions.
46

Copolymerization of styrene and butadiene monomers via miniemulsion /

Li, Donghong, January 1998 (has links)
Thesis (Ph. D.)--Lehigh University, 1998. / Includes vita. Includes bibliographical references.
47

Emulsionen als parenterale Arzneistoffträgersysteme : Herstellung, Optimierung und Charakterisierung /

Bock, Thomas. January 1994 (has links) (PDF)
Univ., Diss.--Kiel, 1994.
48

Preparation of urethane-acrylic hybrid miniemulsion nanoparticles /

Li, Mei, January 2002 (has links)
Thesis (Ph. D.)--Lehigh University, 2002. / Includes bibliographical references and vita.
49

Towards an understanding of steric stabilization when using PEO-PS-PEO triblock copolymer as the stabilizer in the non-aqueous emulsion polymerization systems /

You, Xiaorong, January 1999 (has links)
Thesis (Ph. D.)--Lehigh University, 1999. / Includes vita. Includes bibliographical references.
50

Emulsion polymerizations of styrene and n-butyl acrylate in an automated reaction calorimeter /

Ozdeger, Eser, January 1997 (has links)
Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Includes bibliographical references.

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