Le développement de structures de plus en plus légères et présentant des rapports performances/coût toujours plus élevés est un enjeu permanent dans le domaine des transports. Les matériaux polymères présentent des caractéristiques particulièrement bien adaptées à ces besoins. Ce travail de thèse repose sur le développement d’un matériau polymère destiné à être utilisé en tant que liner de réservoir de stockage d’oxygène liquide (LOX). L’objectif est de démontrer une réduction des masses de l’ordre de 20 à 30%, en comparaison avec des structures métalliques. Pour les besoins de l’application, le matériau à développer se doit de présenter une bonne compatibilité au LOX, une faible perméabilité aux gaz, des propriétés mécaniques suffisamment élevées à basse température ainsi qu’une bonne aptitude à la mise en forme par rotomoulage. La première partie de ces travaux a porté sur la compatibilité au LOX des polymères. En tenant compte des théories proposées dans la littérature, des nanocomposites à matrice polyamide 6 (PA6) ont été élaborés et caractérisés afin d’atteindre les performances recherchées. L’influence de différents paramètres supposés régir la tenue à l’oxygène liquide des matériaux polymères a ensuite été déterminée. Les nanocomposites obtenus présentent globalement une bonne compatibilité avec le LOX. Cette étude a également permis de mettre en évidence que les résultats sont fortement dépendants des paramètres liés à l’échantillonnage. Dans un second temps, la processabilité par rotomoulage de ces nanocomposites PA6 a été évaluée. Les propriétés rhéologiques et de stabilité thermique ont notamment été étudiées. Quelques essais de rotomoulage sur les systèmes les plus pertinents ont également été réalisés et ont démontré des résultats encourageants. Dans une dernière partie, les propriétés barrière aux gaz de ces systèmes PA6 ont été étudiées. Les perméabilités mesurées ont été interprétées en tenant compte de la morphologie des mélanges. En particulier, cette étude montre que les nanocomposites à base de PA6 et de graphite lamellaire présentent des performances adaptées pour l’application en raison de l’effet de tortuosité induit par la charge. Les propriétés mécaniques en traction uniaxiale des systèmes élaborés ont finalement été déterminées et confrontées aux spécifications requises. Les résultats obtenus montrent que les caractéristiques mécaniques sont tout à fait adaptées pour une utilisation en tant que liner de réservoir de stockage d’oxygène liquide. / In the field of transport, the development of lighter, cheaper and more efficient structures is a recurrent challenge. Polymer materials are good candidates for these applications due to their characteristics quite suitable for requirements. This Phd work aims at developing a thermoplastic material which will be used as an internal liner of a liquid oxygen (LOX) storage tank. The objective is to demonstrate a 20 % to 30 % weight saving, compared to metallic structures. To be used in this kind of application, the thermoplastic material must be LOX compatible, processable by rotational moulding and display a low gas permeability as well as good mechanical properties at low temperatures. In a first part, LOX compatibility of polymers was studied. Taking into account theories proposed in the literature, polyamide 6 (PA6) nanocomposites based on LCP, fluoride and graphite fillers were processed and characterized in order to reach desired properties. The influence of several parameters having an impact on LOX behaviour of polymers was then investigated. The nanocomposites show overall good compatibility with liquid oxygen. This study also demonstrates that LOX sensitivity largely depends on the preparation of samples. The processability of nanocomposites by rotational moulding has then been investigated. Rheological properties and thermal stability have especially been studied. Some rotational moulding trials were carried out on the most relevant systems and demonstrate promising results. Finally, the gas transport properties of PA6 nanocomposites were studied. Measured gas permeability was discussed as a function of the morphology of blends. In particular, this study shows that PA6 nanocomposites filled with lamellar graphite present convenient performances which are due to the tortuosity effect induced by the filler. Mechanical properties of filled systems were finally determined and compared with set requirements. The results show that mechanical characteristics are quite relevant for use as internal liner of LOX storage tank.

Ce travail concerne l’étude de la nanostructuration de membranes polymère/métal, réalisées par génération in situ. Nous avons précisé les paramètres chimiques et physicochimiques influant sur la nanostructure de films à matrice alcool polyvinylique et polyétherimide nanostructurés par des nanoparticules d’argent et de palladium, à partir de différents précurseurs et différents solvants de préparation. Nous avons dégagé l’influence des voies de réduction (thermique, radiolytique et chimique) sur la morphologie et sur les propriétés fonctionnelles des films nanocomposites. Globalement, les conditions de nanostructuration employées ont eu un fort impact à la fois sur les tailles des nanoparticules générées et sur leur répartition au sein du film. L’impact de la morphologie a été évalué à son tour sur les propriétés fonctionnelles, c'est-à-dire dans notre cas sur les propriétés mécaniques et sur les propriétés de transport de gaz. L’analyse fine de ces deux types de propriétés nous a permis de préciser les effets de dispersion et le rôle des interfaces nanoparticules/polymère. Nous avons également montré que le transport dans les films nanocomposites polymère/palladium pouvait être analysé et interprété en termes de transport actif. / This work deals with the study of the nanostructuration of polymer/metal membranes, realised by in situ generation. We specified the chemical and physico-chemical parameters influencing the nanostructure of polyvinyl alcohol and polyetherimide matrix films nanostructured by silver and palladium nanoparticles, thanks to different precursors and different preparation solvents. We showed the influence of the nanostructuration processes (thermal, under irradiation and chemical) on the morphology and on the functional properties of the nanocomposite films. On the whole, the nanostructuration conditions had a high impact both on the generated nanoparticles sizes and their organisation in the film thickness. The morphology’s impact was then evaluated on the functional properties, i.e. in our case on the mechanical properties and on the gas transport properties. The analysis of these two types of properties allowed us to specify the dispersion effects and the role of the nanoparticles/polymer interfaces. We also showed that the transport in the polymer/palladium nanocomposite films could be analysed and construed as active transport.

Ce travail de thèse décrit la préparation de deux types de films de polymères : i) des films nanocomposites à base de silice pyrogénée aux propriétés superhydrophobes et ii) des films LbL auto-assemblés, incluant tous deux des dérivés de poly(2,3,4,5,6-pentaflurostyrene) (PPFS), utilisés comme briques élémentaires. La stratégie utilisée ici consiste à exploiter les nombreux avantages que présente la réaction de substitution du fluor en position para du PPFS avec un thiol, pour générer de nouveaux dérivés aux propriétés ajustables. Ainsi, le premier volet de la thèse a consisté à introduire des chaînes de PPFS de façon covalente à la surface de silice pyrogénée par une stratégie dite de «grafting through» en utilisant la polymérisation radicalaire contrôlée par le voir nitroxydes, en présence de PS-DEPN comme macroamorceur. La cinétique de polymérisation du PFS avec et sans particules silice a été étudiée dans divers solvants, différentes particules hybrides de silices modifiées en surface par une couronne de PPFS ont été préparé. Ensuite, un thiol perfluoré (perfluorodecanethiol:PFDT) a été utilisé pour modifier le PPFS, considéré dans ce cadre comme matrice hôte pour la préparation des nanocomposites et pour modifier le PPFS présent à la surface des particules de silice. A partir de là, un large panel de films nanocomposite a été préparé à partir des différentes combinaisons possibles de polymère hôte (PPFS ou PPFS-PFDT) et de charges inorganiques de silice (modifiées par le PPFS ou par le PPFS-PFDT). Les propriétés de mouillabilité ainsi que la morphologie de surface de chaque film ont été analysées et il en résulte que certains films présentent un caractère superhydrophobe. Le deuxième volet de la thèse a porté sur la modification du PPFS par des thiols porteurs de fonctions acide carboxylique, toujours par la réaction de substitution décrite précédemment. Différents dérivés de PPFS carboxylés de DS variés ont été synthétisés. Leur habilité à développer des liaisons hydrogène avec un polymère modèle accepteur de liaison H (la poly(4-vinyl pyridine) (P4VP)) a été étudiée. Il en ressort que dépendamment de la nature du solvant, des mélanges miscibles ou des complexes interpolymères ont ensuite été formés. Des solutions de complexes préformés ont été successivement déposées par spin-coating pour construire des films. De plus, des films multicouches LbL stabilisés par des liaisons H entre le PPFS carboxylé et la P4VP ont été élaborés and il a été démontré que la nature du solvant de dépôt, ainsi que le taux de modification du PPFS, impactent fortement le mécanisme de croissance, l’épaisseur du film et les caractéristiques de surface, en termes de topologie et de mouillabilité. / This work describes the preparation of two kinds of thin polymer films : i) self-cleaning silica-based (nano)composites films and ii) LbL self-assembling films, both including poly(2,3,4,5,6-pentaflurostyrene) (PPFS) derivatives, as building blocks. The cornerstone of the approach is to exploit the thiol-para fluoro substitution reaction to PPFS chains in order to generate derivatives with tailored properties. In this frame, PPFS chains were anchored onto the surface of vinyl-functionalized fumed silica nanoparticles by nitroxide-mediated polymerization (NMP) in presence of PS-DEPN as macro-initiator via a “grafting through” strategy. The kinetics of NMP of PFS were investigated in presence and without silica in various solvents and well-characterized hybrid silica particles containing different polymer grafting weight were declined. Then, perfluorodecanethiol (PFDT) was employed to modify PPFS, considered as the host polymer matrix, and to functionalize PPFS chains tethered to silica particles. A large panel of (nano)composite films from the different possible host matrix/silica particles combinations was prepared. The wettability and the surface morphology of each film were discussed, as a function of the host structure (PPFS or PPFS-PFDT with different DS) and silica (modified with PPFS or PPFS-PFDT), as well as the silica content. It results that superhydrophobic features can be reached. Subsequently, PPFS was modified by using carboxylic acid mercapto modifier via the thiol-para fluoro coupling. Various carboxylated PPFS derivatives differing in the degree of substitution (DS) were prepared and their ability to develop H-bonds in solution with a model strong H-bond acceptor partner (poly(4-vinyl pyridine) (P4VP)) was investigated. Dependently on the nature of the solvent, a miscible blend or interpolymer complexes (IPC) were achieved. IPC-containing solutions were used to successfully fabricate spin-assisted films. Furthermore, H-bonds mediated LbL self-assembly multilayer films involving carboxylated PPFS and P4VP were prepared and it was evidenced that the nature of the deposition solvent as well as the extent of the modification (quantified by the DS), impact the growth mechanism, the thickness and the surface features, in terms of topology and wettability.

Organic coatings are widely used to lower the corrosion rate of metallic structures. However, penetration of water, oxygen and corrosive ions through pores present in the coating results in corrosion initiation and propagation once these species reach the metal substrate. Considering the need for systems that offer active protection with self-healing functionality, composite coatings containing polyaniline (PANI) conducting polymer are proposed in this study. In the first phase of my work, PANI was synthesized by various methods and characterized. The rapid mixing synthesis method was chosen for the rest of this study, providing PANI with high electrical conductivity, molecular structure of emeraldine salt, and morphology of spherical nanoparticles. PANIs doped with phosphoric and methane sulfonic acid revealed hydrophilic nature, and I showed that by incorporating a long-chain alkylphosphonic acid a hydrophobic PANI could be prepared. The second phase of my project was dedicated to making homogenous dispersions of PANI in a UV-curable resin based on polyester acrylate (PEA). Interfacial energy studies revealed the highest affinity of PEA to PANI doped with phosphoric acid (PANI-PA), and no attractive or long-range repulsive forces were measured between the PANI-PA surfaces in PEA.This is ideal for making conductive composites as, along withno aggregation tendency, the PANI-PA particles might come close enough to form an electrically connected network. Highly stable PEA/PANI-PA dispersions were prepared by pretreatment of PANI-PA in acetone followed by mixing in PEA in small portions under pearl-milling. The third phase of my project dealt with kinetics of the free radical polymerization that was utilized to cure the PEA/PANI-PA mixture. UV-vis absorption studies suggested a maximum allowed PANI-PA content of around 4 wt.% in order not to affect the UV curing behavior in the UV-C region. Real-time FTIR spectroscopy studies, using a laboratory UV source, revealed longer initial retardation of the photocuring and lower rates of crosslinking reactions for dispersions containing PANI-PA of higher than 3 wt.%. The presence of PANI-PA also made the formulations more sensitive to changes in UV light intensity and oxygen inhibition during UV curing. Nevertheless, curing of the dispersions with high PANI-PA content, of up to 10 wt.%, was demonstrated to be possible at either low UV light intensities provided the oxygen replenishment into the system was prevented, or by increasing the UV light intensity to very high levels. In the last phase of my project, the PEA and PEA/PANI-PA coatings, cured under high intensity UV lamps, were characterized. SEM analysis showed small PANI-PA particles to be closely packed within the matrix, and the electrical conductivity of the composite films was measured to be in the range of semiconductors. This suggested the presence of a connected network of PANI-PA, as confirmed by investigations of mechanical and electrical variations at the nanoscale by PeakForce TUNA AFM. The data revealed the presence of a PEA-rich layer at the composite-air interface, and a much higher population of the conductive network within the polymer matrix. High current signal was correlated with a high elastic modulus, consistent with the level measured for PANI-PA, and current-voltage studies on the conductive network showed non-Ohmic characteristics. Finally, the long-term protective property of the coatings was characterized by OCP and impedance measurements. Short-term barrier-type corrosion protection provided by the insulating PEA coating was turned into a long-term and active protection by addition of as little as 1 wt.% PANI-PA. A large and stable ennoblement was induced by the coatings containing PANI-PA of up to 3 wt.%. Higher content of PANI-PA led to poorer protection, probably due to the hydrophilicity of PANI-PA facilitating water transport in the coating and the presence of potentially weaker spots in the film. An iron oxide layer was found to fully cover the metal surface beneath the coatings containing PANI-PA after final failure observed by electrochemical testing. / <p>QC 20141103</p>

Reverse electrodialysis (RED) is a technique that can capture electrical potential from mixing two water streams of different salt concentration through permselective ion exchange membranes. Effective design of ion exchange membranes through structure optimization is critical to increase the feasibility of salinity gradient power production by RED. In this work, we present the preparation of organic-inorganic nanocomposite cation exchange membranes containing sulfonated polymer, poly (2,6-dimethyl-1,4-phenylene oxide), and sulfonated silica (SiO2-SO3H). The effect of silica filler size at various loading concentrations on membrane structures, electrochemical properties, and the RED power performance is investigated. The membranes containing bigger-sized fillers (70 nm) at 0.5 wt% SiO2-SO3H exhibited a relatively favorable electrochemical characteristic for power performance: an area resistance of 0.85 Ω cm2, which is around 9.3% lower than the resistance of the membranes with smaller filler particles. The power performance of this nanocomposite cation exchange membrane in a RED stack showed 10% higher power output compared with the membranes containing small particle size and achieved the highest gross power density of 1.3 W m-2. Thus, further optimized combination of material properties and membrane structure is a viable option for the development of effective ion exchange membrane design, which could provide desirable electrochemical performance and greater power production by RED.

With the development of modern industrial engineering technology, increasing demands of multifunctional materials drive the exploration of new applications of electrical conductive polymer nanocomposites (CPNCs). Toward applications of smart materials, sensing performance of CPNCs has gained immense attention in the last decade. Among them, strain sensors, based on piezoresistive behavior of CPNCs, are of high potential to carry out structural health monitoring (SHM) tasks. Poly(vinylidene fluoride) (PVDF) is highly thought to be potential for SHM applications in civil infrastructures like bridges and railway systems, mechanical systems, automobiles, windgenetors and airplanes, etc. because of its combination of flexibility, low weight, low thermal conductivity, high chemical corrosion resistance, and heat resistance, etc. This work aimed to achieve high piezoresistive sensitivity and wide measurable strain ranges in carbon nanotube based poly(vinylidene fluoride) (PVDF) nanocomposites. Four strategies were introduced to tune the sensitivity of the relative electrical resistance change (ΔR/R0) versus the applied tensile strain for such nanocomposites. Issues like the influence of dispersion of multi-walled carbon nanotubes (MWCNTs) on initial resistivity of PVDF nanocomposites and conductive network structure of MWCNTs, as well as piezoresistive properties of the nanocomposites, were addressed when using differently functionalized MWCNTs (strategy 1). In addition, the effects of crystalline phases of PVDF, mechanical ductility of its nanocomposites and interfacial interactions between PVDF and fillers on piezoresistive properties of PVDF nanocomposites were studied. Using hybrid fillers, to combine MWCNTs with conductive carbon black (strategy 2) or isolating organoclay (strategy 3), piezoresistive sensitivity and sensing strain ranges of PVDF nanocomposites could be tuned. Besides, both higher sensitivity and larger measurable strain ranges are achieved simultaneously in PVDF/MWCNT nanocomposites when using the ionic liquid (IL) BMIM+PF6- as interface linker/modifier (strategy 4). The detailed results and highlights are summarized as following: 1. The surface functionalization of MWCNTs influences their dispersion in the PVDF matrix, the PVDF-nanotube interactions and crystalline phases of PVDF, which finally results in different ΔR/R0 and the strain at the yield point (possibly the upper limit of sensing strain ranges). As a whole, regarding to the fabrication of strain sensors based on PVDF/MWCNT nanocomposite, in contrast to pristine CNTs, CNTs-COOH and CNTs-OH, CNT-NH2 filled PVDF nanocomposites possess not only high piezoresistive sensitivity but also wide measurable strain ranges. Gauge factor, i.e. GF, is ca.14 at 10% strain (strain at the yield point) for the nanocomposites containing 0.75% CNTs-NH2. 2. Using hybrid fillers of CNTs and CB to construct strain-susceptible network structure (conductive pathway consisting of string-like array of CNTs and CB particles) enhances the piezoresistive sensitivity of PVDF nanocomposites, which is tightly associated with the CNT content in hybrid fillers and mCNTs/mCB. The best piezoresistive effect is achieved in PVDF nanocomposites with fixed CNT content lower than the ΦC (0.53 wt. %) of PVDF/CNT nanocomposites. 3. ΔR/R0 and possible sensing strain ranges of PVDF nanocomposites were tailored by changing crystalline phases of PVDF and PVDF-MWCNT interactions. Besides, the increase of the strain at yield point in PVDF nanocomposites filled by CNTs-OH is more obvious than that in the nanocomposites containing the same amount of clay and CNTs. The nanocomposite consisting of 0.25% clay and 0.75% CNTs-OH have ca. 70% increase of the strain at the yield point (17%) and the GF at this strain is ca. 14, while GF for the nanocomposite filled by only 0.75% CNTs-OH is ca. 5 at 10% strain. 4. IL BMIM+PF6- served as interface linker for PVDF and MWCNTs, which significantly increased the values of ΔR/R0 and strain at the yield point of PVDF nanocomposites simultaneously. Besides, this increases with increasing IL content. With the aid of IL, the dispersion of nanotube and toughness of the nanocomposites are greatly improved, but the electrical conductivity of the nanocomposites is decreased with the incorporation of IL, which is related to the IL modified PVDF-MWCNT interface connection or bonding. GF reaches ca. 60 at 21% strain (the strain at the yield point) for PVDF nanocomposites filled by 10% IL premixed 2%CNTs-COOH.

Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Future chemical production is faced with a challenge of limited material and energy resources. However, process intensification might play a significant role to alleviating this problem. Vision of process intensification through multifunctional reactors has stimulated research on membrane-based reactive separation processes, in which membrane separation and catalytic reaction occur simultaneously in one unit. These processes are rather attractive applications because they are potentially compact, less capital intensive, and have lower processing costs than traditional processes. Moreover, they often enhance the selectivity and yield of the target product. For about three decades, there has been a great evolution in p-Xylene production technology, with many equipment improvements being instituted in the industry. Typically, these improvements bring economic as well as processing advantages to the producers. Such developments are vital, as the capital costs for process equipment to produce and separate p-Xylene from xylene isomers, especially into high purity p-Xylene, still remain very high. However, with numerous advantages of membrane-based reactive separation processes compared to the conventional processes, the research focus has been channelled toward application of MFI-type zeolite membranes for in situ separation and isomerization of xylene in extractor-type catalytic membrane reactors. To contribute to this research line, this study has focused on characterization and optimization of an extractor-type catalytic membrane reactor (e-CMR) equipped with a nanocomposite MFI-alumina membrane as separation unit for m-Xylene isomerization over Pt-HZSM-5 catalyst. Nanocomposite MFI-alumina zeolite membranes (tubes and hollow fibres) used in this study were prepared via a so-called “hydrothermal pore-plugging synthesis technique” developed by Dalmon and his group more than a decade ago. In this concept, MFI material is grown by 'pore-plugging' direct hydrothermal synthesis in a porous matrix rather than forming thin films on top of the support. The advantages of this type of architecture over conventional film-like zeolite membranes include: (i) minimization of the effect of thermal expansion mismatch between the support and the zeolite, (ii) easy to scale-up, and (iii) easy module assembly, because the separative layer (zeolite crystals) are embedded within the pores of the ceramic support, reducing the effects of abrasion and thermal shocks. After membrane synthesis, the membrane quality and separation performance of these membranes were evaluated through single gas permeation (H2), binary gas separation (n-butane/H2) and ternary vapour mixture of xylene isomers using the vapour permeation (VP) method with p-Xylene as the target product. After evaluating the xylene isomer separation performance of the membranes, the membranes were used in extractor-type catalytic membrane reactors to carry out m-Xylene isomerization over Pt-HZSM-5 catalyst with p-Xylene as the target product. This dissertation has shown that nanocomposite MFI-alumina membrane tubes and hollow fibre membranes were selective to p-Xylene from xylene isomers. The dissertation also reports for the first time in open literature the excellent xylene separation performance of nanocomposite MFI-alumina membrane tubes at higher xylene loading (or vapour pressure). Unlike their film-like counterparts, the membranes still maintain increased selectivity to p- Xylene at higher xylene vapour pressures without showing a drastic decrease in selectivity. This outstanding property makes it a promising choice for pervaporation applications where concentration profile is usually a major problem at higher loading of xylene. With the use of nanocomposite MFI-alumina hollow fibre membranes, this research has demonstrated that membrane configuration and effective membrane wall thickness play a prominent role in enhancing cross membrane flux. Results presented in the study show, for the first time in open literature, that nanocomposite MFI-alumina hollow fibre membrane could enhance p-Xylene fluxes during the separation of ternary vapour mixture of xylene due to the smaller effective wall thickness of the membrane (membrane thickness <1 μm) when compared to conventional randomly oriented MFI zeolite films (membrane thickness >3 μm). During xylene isomers separation with nanocomposite hollow fibre membrane, about 30% increase in p-Xylene flux was obtained compared to the membrane tubes, operated under the same conditions. Additionally, hollow fibres offer the added advantage of membrane surfaceto- volume ratios as high as 3000 m2/m3 compared to conventional membrane tubes. Using this type of system could be instrumental in reducing both the size and cost of permeating modules for future xylene separation processes. However, obtaining high quality nanocomposite MFI-alumina membrane fibres is subject to the availability of high quality fibre supports. Regarding the application of nanocomposite MFI-alumina membrane tubes as extractor-type catalytic membrane reactors (referred to as extractor-type zeolite catalytic membrane reactor (e-ZCMR) in this study) for m-Xylene isomerization over Pt-HZSM-5, the results presented in this study further substantiate and confirm the potentials of e-ZCMRs over conventional fixed-bed reactors (FBRs). In the combined mode (products in the permeate plus products in the retentate), the e-ZCMR displayed 16-18% increase in p-Xylene yield compared to an equivalent fixed-bed reactor operated at the same operating conditions. On the basis of the high p-Xylene-to-o-Xylene (p/o) and p-Xylene-to-m-Xylene (p/m) separation factors offered by the membranes, p-Xylene compositions in the permeate-only mode (products in the permeate stream) in the range 95%-100% were obtained in the e-ZCMR. When a defect-free nanocomposite MFI-alumina membrane tube with p-Xylene-too- Xylene (p/o) separation factor >400 was used, ultra pure p-Xylene with p-Xylene purity approaching 100% in the permeate-only mode was obtained. Moreover, the e-ZCMR displayed 100% para-selectivity in the permeate-only mode throughout the temperatures tested. This is not possible with conventional film-like MFI-type zeolite membranes. Therefore, the application of nanocomposite MFI-alumina membranes in extractor-type catalytic membrane reactors could catalyse the development of energy-efficient membrane-based process for the production of high purity p-Xylene. Furthermore, in this dissertation, a report on modelling and sensitivity analysis of an e-ZCMR equipped with a nanocomposite MFI-alumina membrane tube as separation unit for m-Xylene isomerization over Pt-HZSM-5 catalyst is presented. The model output is in fair agreement with the experimental results with percentage errors (absolute) of 17%, 29%, 0.05% and 19.5% for p-Xylene yield in combined mode, p-Xylene selectivity in combined mode, p-Xylene selectivity in permeate-only mode and m-Xylene conversion, respectively. Therefore, the model is adequate to explain the behaviour of e-ZCMR during m-Xylene isomerization over Pt-HZSM-5 catalyst. The model is also adaptable to e-ZCMRs of different configurations such as hollow fibre MFI-alumina membrane-based e-ZCMRs. To gain more insight into the behaviour of the model to small changes in certain design parameters, sensitivity analysis was performed on the model. As expected, the sensitivity analysis revealed that intrinsic property of membrane (porosity, tortuosity), membrane effective thickness and reactor size (indicated with reactor internal diameter) play a significant role on the performance of e-ZCMR during p-Xylene production from the mixed xylenes. MFI-alumina zeolite membranes with optimized parameters such as membrane porosity, membrane tortuosity, and membrane effective wall thickness might enhance transport of p-Xylene through the membrane and thus resulting in higher p-Xylene flux through the membrane. This eventually would translate into an increase in p-Xylene yield in permeate-only mode. As far as it could be ascertained, this is the first report in open literature on modelling study with sensitivity analysis of e-ZCMR equipped with nanocomposite MFI-alumina membrane tubes as separation unit for m-Xylene isomerization over Pt-HZSM- 5 catalyst. In addition, the results of this study have confirmed previous research efforts reported on the application of extractor-type catalytic membrane reactors, having MFI-type membranes as separation units, for p-Xylene production via m-Xylene isomerization over a suitable catalyst. Also, new ideas were developed, tested and proposed that now provide a solid basis for further scale-up and techno-economical studies. Such studies are necessary to evaluate the competitiveness of the technology with the traditional processes for the production of high purity p-Xylene from mixed xylene. In summary, the encouraging results, as documented in this dissertation and also communicated to researchers in the area of membrane-based reactive separation (in the form of four peer-reviewed international scientific publications and four conference proceedings), could provide a platform for developing a scaled-up membrane-based energy-efficient industrial process for producing high purity p-Xylene through isomerization. / AFRIKAANSE OPSOMMING: Die produksie van chemiese stowwe word belemmer deur die uitdaging van beperkte materiaal- en energiebronne. Prosesuitbreiding kan egter ‘n noemenswaardige rol in die verligting van hierdie probleem speel. Die moontlike gebruik van multi-funksionele reaktore in prosesuitbreiding het navorsing in membraan-gebaseerde reaktiewe skeidingsprosesse (waar membraanskeiding en die katalitiese reaksie gelyktydig in ‘n enkele eenheid plaasvind) aangemoedig. Hierdie prosesse is aantreklik omdat hulle potensieel kompak en minder kapitaal-intensief is en ook teen laer koste as tradisionele prosesse bedryf kan word. Dit is ook dikwels die geval dat die multi-funksionele reaktor die selektiwiteit en opbrengs van die gewenste produk verhoog. In die afgelope drie dekades was daar ’n sterk verandering in die tegnologie wat gebruik word in die produksie van p-Xileen, met vele verbeterings aan nuwe toerusting wat in die nywerheid in bedryf gestel is. Hierdie verbeteringe hou gewoonlik ekonomiese-, sowel as bedryfsvoordele vir die produsente in. Ontwikkelings in hierdie veld is noodsaaklik aangesien die kapitale uitgawes vir die toerusting om p-Xileen, veral baie suiwer p-Xileen, van xileenpolimere te produseer en te skei, steeds baie hoog is. Met talle voordele gekoppel aan membraangebaseerde reaktiewe skeidingsprosesse in vergelyking met normale prosesse, is die navorsing egter gekanaliseer na die gebruik van MFI-tipe zeolietmembrane vir die in-situ skeiding en isomerisasie van xileen in ekstraksie-tipe katalitiese membraanreaktore. As bydrae tot hierdie navorsingsveld het hierdie studie op die karakterisering en optimering van ‘n ekstraksie-tipe katalitiese membraanreaktor (e-KMR), toegerus met ’n nanosaamgestelde MFI-alumina membraan as skeidingseenheid vir m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM-5 katalis, gefokus. Nanosaamgestelde MFI-alumina zeolietmembrane (buise en hol vesels) wat in hierdie studie gebruik is, is voorberei deur die sogenaamde “hidrotermiese porie-sperring sintese tegniek” wat meer as ‘n dekade gelede ontwikkel is deur Dalmon en sy groep. In hierdie tegniek word MFI-materiaal gekweek deur direkte hidrotermiese sintese in ‘n poreuse matriks, eerder as die vorming van dun films bo-op die ondersteuningsbasis. Die voordele van hierdie ontwerp bo dié van die konvensionele filmagtige zeolietmembrane sluit in: (i) minimering van die effek van termiese uitsetting op die gaping tussen die ondersteuningsbasis en die zeoliet, (ii) die gemak van opskalering, en (iii) die gemak waarmee die modules aanmekaar gesit kan word, omdat die skeidingslaag (zeolietkristalle) binne die porieë van die keramiek-ondersteuningsbasis geleë is, wat die effek van erodering en termiese skok verminder. Ná die membraansintese is die membraankwaliteit en skeidingsvermoë geevalueer deur enkel-gas-deurdringing (H2), binêre-gas-skeiding (n-butaan/H2), en ternêre dampmengsel van xileen-isomere deur die gebruik van die damp-deurdringingsmetode met p-Xileen as die teikenproduk. Hierdie tesis het gewys dat nanosaamgestelde MFI-alumina membraanbuise en hol vesel membrane selektief was ten opsigte van p-Xileen vanuit xileen-isomere. Die tesis doen ook, vir die eerste keer in die oop literatuur verslag, oor die uitstekende p-Xileen skeidingsvermoë van nanosaamgestelde MFI-alumina buise by hoër xileenladings (of dampdrukke). Anders as hulle filmagtige eweknieë het die membrane steeds hul verhoogde selektiwiteit vir p-Xileen by hoër dampdrukke behou, sonder ‘n merkbare verlaging in die selektiwiteit. Hierdie merkwaardige eienskap maak dit ‘n belowende keuse vir pervaporasie toepassings, waar die konsentrasieprofiel (as gevolg van hoër xileenladings) gewoonlik ’n noemenswaardige probleem is. Met die gebruik van nanosaamgestelde MFI-alumina membrane het hierdie navorsing gewys dat membraankonfigurasie en –wanddikte ‘n prominente rol speel in die verbetering van vloei oor die membraan. Resultate wat in die studie voorgelê word, wys, vir die eerste keer in oop literatuur, dat hol vesel nanosaamgestelde MFI-alumina membrane die deurvloei van p-Xileen kan verbeter gedurende die skeiding van ternêre dampmengsels van xileen, as gevolg van die kleiner effektiewe wanddikte van die membraan (<1 μm) wanneer dit vergelyk word met konvensionele kansgewys-geörienteerde MFI-zeoliet films met ‘n membraandikte van >3 μm. Tydens die skeiding van xileen-isomere met nanosaamgestelde hol vesel membrane is ‘n verbetering van ongeveer 30 % in die deurvloei van p-xileen verkry, vergeleke met membraanbuise, by identiese bedryfstoestande. Hol vesels bied ook die verdere voordeel van oppervlak-tot-volume verhoudings van so hoog as 3000 m2/m3 vergeleke met konvensionele membraanbuise. Die gebruik van hierdie tipe sisteem kan deurslaggewend wees in die vermindering van die grootte en koste van deurlatingseenhede in toekomstige xileen-skeidingsprosesse. Die vervaardiging van hoë-kwaliteit nanosaamgestelde MFIalumina membraanvesels is egter onderworpe aan die beskikbaarheid van hoë-kwaliteit vessel-ondersteuningsbasisse. Wat die gebruik van nanosaamgestelde MFI-alumina membraanbuise as ekstraksietipe katalitiese membraanreaktore betref (ekstraksie-tipe zeoliet katalitiese membraanreaktor, of e-ZKMR in hierdie studie) vir m-Xileen isomerisasie in die teenwoordigheid Pt-HZSM-5, bevestig die resultate die potensiaal van e-ZKM reaktore bo konvensionele vaste-bed reaktore (VBR). In die gekombineerde verstelling (met produkte in die permeaat sowel as die retentaat) toon die e-ZKMR ‘n 16 – 18% verbetering in die opbrengs van p-Xileen vergeleke met ‘n ekwivalente VBR by dieselfde bedryfskondisies. Gegrond op die hoë p-Xileen-tot-o- Xileen (p/o) en p-Xileen-tot-m-Xileen (p/m) skeidingsfaktore wat deur die membraan gebied word, is p-Xileen-samestellings in die slegs-permeaat verstelling (produkte in die permeaatstroom) van tussen 95 en 100% in die e-ZKMR verkry. Toe ‘n defek-vrye nanosaamgestelde MFI-alumina membraanbuis met ‘n (p/o) skeidingsfaktor van >400 gebruik is, is p-Xileen met ‘n suiwerheid na aan 100% in die slegs-permeaat verstelling verkry. Die e-ZKMR het ook 100% para-selektiwiteit in die slegs-permeaat verstelling getoon by alle toets-temperature, iets wat onmoontlik is met gewone filmagtige MFI-tipe zeolietmembrane. Om hierdie rede is dit moontlik dat die gebruik van MFI-alumina membrane in ekstraksie-tipe katalitiese membraanreaktore die ontwikkeling van energie-doeltreffende membraangebaseerde prosesse vir die produksie van suiwer p-Xileen kan bevorder. Verder word daar in hierdie tesis verslag gedoen oor die modelering en sensitiwiteitsanalise van ‘n e-ZKMR wat toegerus is met ‘n nanosaamgestelde MFI-alumina membraanbuis as skeidingseenheid vir m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM-5 katalis. Die model-uitsette is redelik in ooreenstemming met eksperimentele resultate met absolute fout-persentasies van 17, 27, 0.05 en 19.5 % vir die p-Xileen opbrengs in die gekombineerde verstelling, p-Xileen selektiwiteit in die gekombineerde verstelling, p-Xileen selektiwiteit in die slegs-permeaat verstelling en m-Xileen omsetting, onderskeidelik. Om hierdie rede kan die model die gedrag van ‘n e-ZKMR verduidelik tydens die m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM-5 katalis. Die model kan ook aangepas word na e-ZKM reaktore met verskillende konfigurasies, soos hol vesel MFIalumina membraan-gebaseerde e-ZKMRe. Om meer insig te kry in die gedrag van die model op klein veranderinge in sekere ontwerpparameters, is ‘n sensitiwiteitsanalise op die model uitgevoer. Soos verwag, het die sensitiwiteitsanalise gewys dat die intrinsieke eienskappe van die membraan (porositeit, tortuositeit), die effektiewe van membraandikte en die reaktorgrootte (gemeet as die interne deursnit van die reaktor) ‘n noemenswaardige rol speel in die gedrag van die e-ZKMR gedurende p-Xileen produksie vanuit gemengde xilene. MFI-alumina zeolietmembrane met geoptimeerde parameters soos membraanporositeit, -tortuositeit, en –wanddikte mag dalk die oordrag van p-Xileen deur die membraan bevorder en sodoende ‘n hoër vloei van p-Xileen oor die membraan bewerkstellig. Dit sal uiteindelik lei tot ‘n verhoging in die opbrengs van p-Xileen in die slegs-permeaat verstelling. So ver dit vasgestel kon word, is hierdie die eerste verslag in die oop literatuur wat die modelering en sensitiwiteitsanalise van ‘n e-ZKMR, toegerus met nanosaamgestelde MFIalumina membraanbuise as skeidingseenheid vir m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM katalis, aanspreek. Verder ondersteun die resultate van hierdie studie vorige navorsingspogings op die gebruik van e-KMRe, met MFI-tipe membrane as skeidingseenhede, vir die produksie van p-Xileen deur middel van m-Xileen isomerisasie in die teenwoordigheid van ‘n geskikte katalis. Verder is nuwe idees ontwikkel, getoets en voorgestel wat dien as ’n stewige basis vir verdere opskalering- en tegno-ekonomiese studies. Sodanige studies is nodig om die vatbaarheid van die tegnologie relatief tot die tradisionele prosesse te bepaal. Ter opsomming, die bemoedigende resultate, soos in die tesis gedokumenteer (en ook gepubliseer in vier ewe-knie beoordeelde internasionale wetenskaplike joernale en vier konferensiestukke), kan as ‘n platform dien vir die ontwikkeling van ’n opgeskaleerde membraan-gebaseerde energie-doeltreffende nywerheidsproses vir die produksie van suiwer p-Xileen deur middel van isomerisasie.

Organic coatings are frequently applied to metals, often in circumstances where there is a need to protect the substrate from corrosion or to improve the aesthetic quality of a product. Increasingly, coatings are also expected to provide additional functionality, such as anti-bacterial properties. Concurrent with the need to satisfy ever more demanding specifications, coating formulators are being obliged to comply with stringent environmental legislation. A research area which may benefit the development of coating formulations is that of nanocomposite synthesis, in which the composite additives have at least one dimension in the nanometre size range. The current research has sought to modify a waterborne organic coating primer with two types of nano-sized additives: layered clays and titanium dioxide nanoparticles. Dispersion of the particles at loadings up to 5% w/w was achieved by ball milling and the modified coatings were subjected to numerous tests to ascertain the effect of the additives. Titanium dioxide was found to improve the tribological properties and corrosion resistance of the coatings, while the addition of magnesium aluminium hydroxycarbonate (hydrotalcite) layered clay had a deleterious effect. Some coatings exhibited a cracked morphology, although no correlation between particle loading and the presence of cracks could be determined. A preliminary investigation into substrate preparation was also conducted. This ensured that the degree of cleanliness of the hot-dip galvanized substrates was both satisfactory and consistent.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Two series of amphiphilic, organic-inorganic graft copolymers of poly(methyl methacrylate) and poly(dimethylsiloxane) (PMMA-graft-PDMS), as well as poly(acrylonitrile) and poly(dimethylsiloxane) (PAN-graft-PDMS), were synthesized via conventional free radical copolymerization using the ―grafting through‖ technique. In both series the PDMS macromonomer content varied from 5 wt.% - 25 wt.% and different graft lengths of 1000 g/mol and 5000 g/mol were used. A gradient elution profile was developed to monitor the removal of the unreacted PDMS macromonomer using hexane extraction. In the case of the PAN copolymer series, the gradient profile showed that as the PDMS content in the feed increased, more PAN-graft-PDMS molecules formed relative to homopolymer PAN. In the case of the PMMA copolymer series, mostly PMMA-graft-PDMS molecules were formed as the PDMS content in the feed increased. In the case of the PAN-graft-PDMS series, the PDMS content affected the crystallization behaviour of the PAN segments and lead to a decrease in crystallinity across the composition range as the PDMS content increased. It is shown that the synthesized graft copolymers can be electrospun to produce continuous nanofibers. The effects of polymer solution concentration, copolymer composition and tip-to-collector distance on the fiber morphology are discussed. The rapid stretching of the polymer jet, as well as the rapid solvent evaporation during the electrospinning process, resulted in highly complex nonequilibrium morphologies in the case of the electrospun PAN-graft-PDMS copolymers. The crystallization behaviour of the electrospun fibers of PAN-graft- PDMS was shown to be different from the unprocessed precursor material. Surface oxidised MWCNTs were successfully incorporated and well dispersed into the graft copolymers via the electrospinning process to produce nanocomposite nanofibers. In the case of the PAN-graft-PDMS copolymer series, the presence of MWCNTs in the nanocomposite nanofibers enhanced the overall degree of crystallinity when compared to the unfilled nanofibers. For the first time positron annihilation lifetime spectroscopy (PALS) analysis was performed on the various complex graft copolymer compositions and their electrospun fiber analogues, as well as nanocomposites, to investigate the free volume properties of the various materials. The results revealed that there are two distinct ortho-positronium (o-Ps) lifetime parameters for these complex multiphased materials. The shorter lived lifetime -3 was attributed to the o-Ps annihilation in the amorphous regions of the crystalline PAN phase in the PAN-graft-PDMS copolymer series, as well as to the o-Ps annihilation in the amorphous PMMA phase in the case of the PMMA-graft-PDMS copolymer series. The longer lived lifetime -4 was attributed to the o-Ps annihilation in the more amorphous PDMS phase. In the case of the PMMA series the relative fractional free volume was influenced by the graft lengths, where the 5000 g/mol series showed a larger increase in fractional free volume relative to the shorter 1000 g/mol series. The effects of the tip-to-collector distance during electrospinning, as well as the inclusion of MWCNTs, on the free volume properties are also discussed. It is demonstrated how positron annihilation lifetime spectroscopy can provide valuable and unique information on the internal structure and morphology of the electrospun nanofibers. / AFRIKAANSE OPSOMMING: Twee reekse amfifiliese, organies-anorganiese entkopolimere van poli(metielmetakrilaat) en poli(dimetielsiloksaan) (PMMA-ent-PDMS), asook poli(akrilonitriel) en poli(dimetielsiloksaan) (PAN-ent-PDMS), is gesintetiseer deur konvensionele vrye-radikaalkopolimerisasie. Die PDMS makromonomeerinhoud het gewissel tussen 5 wt.% - 25 wt.% in albei reekse en sykettinglengtes van 1000 g/mol en 5000 g/mol is gebruik. `n Gradient-eluasieprofiel is opgestel om die verwydering van ongereageerde PDMS makromonomeer d.m.v. heksaanekstraksie te monitor. In die PAN kopolimeer reeks het die gradient-eluasieprofiel gewys dat meer PAN-ent- PDMS molekules vorm relatief tot die PAN homopolimeer sodra meer PDMS bygevoeg word. In die PMMA kopolimeer reeks het meer PMMA-ent-PDMS molekules gevorm sodra meer PDMS toegevoeg is. In die geval van die PAN-ent- PDMS reeks, het die PDMS die kristallisasiegedrag van die PAN segmente geaffekteer en `n afname in die totale kristalliniteit veroorsaak soos die PDMS inhoud vermeerder het. Daar word bewys dat die gesintetiseerde entkopolimere geelektrospin kan word om nanovesels te vorm. Die effek van polimeeroplossingskonsentrasie, kopolimeersamestelling en punt-tot-versamelaarafstand op die nanoveselmorfologie word bespreek. Die vinnige strekking van die polimeerjet sowel as die vinnige verdamping van die oplosmiddel gedurende die elektrospinproses het gelei tot hoogs komplekse nie-ekwilibrium morfologieë in die geval van die ge-elektrospinde PAN-ent-PDMS kopolimere. Die kristallisasiegedrag van die nanovesels van PAN-ent-PDMS het verskil van die onverwerkte voorloper materiaal. Oppervlakgeoksideerde MWCNTs is suksevol geïnkorporeer en versprei in die entkopolimere d.m.v. die elektrospinproses om nanosaamgestelde nanovesels te vorm. Die teenwoordigheid van MWCNTs in die nanosaamgestelde nanovesels in die PAN-ent-PDMS kopolimeerreeks het gelei tot `n verbetering in die algehele kristalliniteit in vergelyking met die nanovesels sonder MWCNTs. Positronvernietigingsleeftyd- spektroskopie (PALS) is vir die eerste keer gebruik om die vrye volume van verskillende kompleks entkopolimeersamestellings, hul ge-elektrospinde nanovesels sowel as nanosaamgestelde nanovesels te bestudeer. Die resultate het getoon dat daar twee verskillende orto-positronium (o-Ps) leeftydparameters vir hierdie komplekse multifase materiale bestaan. Die korter leeftydparameter -3 word toegeskryf aan die o-Ps vernietiging in die amorfe areas van die kristallyne PAN fase in die PAN-ent-PDMS kopolimeerreeks, sowel as die o-Ps vernietiging in die amorfe PMMA fase in die PMMA-ent-PDMS kopolimeerreeks. Die langer leeftydparameter -4 word toegeskryf aan die o-Ps vernietiging in die amorfe PDMS fase. Die relatief fraksionele vrye volume van die PMMA reeks is deur die verskillende syketting lengtes beïnvloed. Die 5000 g/mol syketting het `n groter toename in fraksionele vrye volume veroorsaak relatief tot die korter 1000 g/mol syketting. Die effek van die punttot- versamelaar-afstand tydens die elektrospinproses op die vrye volume eienskappe, sowel as die insluiting van MWCNTs, word bespreek. Daar word aangedui hoe positron-vernietigingsleeftyd-spektroskopie waardevolle en unieke inligting kan verskaf oor die interne struktuur en morfologie van die nanovesels.

The development of efficient, high-performance materials for electrical energy storage and conversion applications has become a must to meet an ever-increasing need for electrical energy. Among devices developed for this purpose, capacitors have been used for pulsed power applications that require large power density with millisecond-scale charge and discharge. However, conventional polymeric films, which possess high breakdown strength, are limited due to low permittivity and hence compromise the energy storage capability of capacitors. In order to develop high energy density dielectric materials for pulsed power applications, two hurdles must be overcome: 1) the appropriate selection of materials that possess not only large permittivity but also high breakdown strength, 2) the optimization of material processing to improve morphology of dielectric films to minimize loss during energy extraction process. This thesis will present the development of novel dielectric material, with emphasis on the optimization of material and thin film processing toward improved morphology as ways to achieve high energy density at the material level. After first two chapters of introduction and experimental details, Chapter 3 will demonstrate the improvement of nanocomposite morphology via processing optimization and study its effect on the energy storage characteristics of nanocomposites thereof. Chapter 4 will investigate dielectric sol-gel materials containing dipolar cyano side groups, which are relatively a new class of material for pulsed power applications. Finally, Chapter 5 will discuss the effect of tunneling barrier layer on sol-gel films to mitigate charge carrier injection and associated conduction and breakdown phenomena, which would be significantly detrimental to the energy storage performance of dielectric sol-gel films.