Ce travail a pour objectif le développement et l’analyse du comportement de films nanocomposites en poly(acide lactique) (PLA), obtenus par extrusion gonflage, pour application textile à usage unique. L’utilisation du PLA, est justifiée par son origine naturelle et ses bonnes performances physiques. Il présente néanmoins quelques limites compte tenu de l’application visée (notamment en termes de sensibilité à la dégradation thermique, aptitude au gonflage et souplesse) nécessitant sa modification par des plastifiants et des agents de branchement dont l’efficacité est tout d’abord évaluée. L’ajout de nanocharges est justifié par les performances de barrière attendues. Deux argiles, associées à divers traitements de surface, sont incorporées à la matrice PLA modifiée à l’état fondu, par extrusion. L’état de dispersion est caractérisé par un couplage de techniques globales (rhéologie, microscopie électronique à balayage) ou locales (diffraction des rayons X, microscopie électronique par transmission) et permet de juger de l’efficacité des traitements proposés. Les nanocomposites ainsi élaborés sont utilisés pour la fabrication de films par extrusion gonflage. La caractérisation de leurs performances mécaniques et de barrière permet alors d’optimiser la formulation compte tenudes contraintes imposées par le cahier des charges de l’application visée. Enfin, la ténacité de films soufflés est caractérisée par la méthode du travail essentiel de rupture dont la validité est analysée sur la base de mesures de champs cinématiques pour certaines de ces formulations. / The aim of this work is the development and the behavior analysis of blown nanocomposite films based on polylactic acid (PLA), obtained by extrusion-blowing for single-use textile application. The use of the PLA is justified by its natural origin and by its good physical properties. However, PLA presents some limits (in particular, in terms of sensibility to the thermal degradation, processabilty by extrusion-blowing and flexibility) requiring its modification by branching and plasticization. Te efficiency of these modifications was estimated first of all. Adding Nanoclay is justified by the barrier properties aimed. Two nanoclays, associated to different surface treatment, were incorporated to PLA by melt intercalation using an extruder. The dispersion level of the modified clays was analyzed by global techniques (rheology, scanning electron microscopy) or local techniques (X-ray diffraction, transmission electron microscopy) and leads to characterize the efficiency of clay treatments. Nanocomposites so elaborated were used for manufacturing films by extrusion-blowing. The characterization of their mechanical and barrier properties allowed to optimize the film composition considering the aimed application. Finally, film tenacity was studied by the essential work of fracture method for blown films. The relevance of this method is studied via the validation of hypotheses necessary for its application. The technique that measures the displacement field has allowed us to study two of these hypotheses.

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The purpose of this study was to determine whether magnetic resonance imaging (MRI) accurately predicts surgical findings in dachshund dogs with thoracolumbar intervertebral disc extrusions (TLDE). Sixteen dogs presenting with signs of acute TLDE took part in this investigation. MRI was performed on each dog. This was followed by decompressive surgery with the completion of an intra-operative questionnaire documenting the site of the extrusion and spatial distribution of the disc material for each dog. An independent veterinary radiologist evaluated each MRI study, measured and recorded the same parameters from images, utilising 3 sequences (T1-, T2-weighted and Short T1 Inversion recovery) without knowledge of the surgical findings. The imaging findings were compared with the intra-operative measurements. The specific intervertebral disc (IVD) space from which the material extruded and lateralization of the extruded disc material (EDM) were found to be similar between MRI and surgical observations. Longitudinal distribution of the EDM was described as being cranial, caudal or equally distributed in relation to the affected IVD. A Kappa test showed moderate agreement in longitudinal distribution between MRI and surgery. Circumferential distribution was recorded on transverse images and compared to surgical findings. Recorded distribution only coincided completely in 1 case, although the rest of the cases showed good overlap of findings between the MRI and intraoperative findings.Our results could not demonstrate a statistically significant difference between T1-, T2-weighted or STIR sequences when determining the length of the extruded mass in the vertebral canal. We found that when evaluating the absolute error and range of error for each sequence, that the T2-weighted sequence had a narrower range of errors and was thus more consistent in predicting the size of the lesion pre-surgically. MRI was validated as a very useful imaging modality for neurological disorders in dogs. / Dissertation (MMedVet)--University of Pretoria, 2007. / Companion Animal Clinical Studies / unrestricted

The composites industry can be positively influenced by composite materials that are processed faster, are lighter in weight, are higher in stiffness and strength, and that are more recyclable. There has been considerable interest in the use of thermotropic liquid crystalline polymers (TLCPs) to reinforce thermoplastic materials. In a novel process developed by Baird and coworkers, wholly thermoplastic composites are produced via a patented, dual extrusion process. This unique process yields a fiber which consists of numerous continuous fibrils of the liquid crystalline polymer encased in a thermoplastic matrix. These fibers have been used to form random mats and woven pre-forms, which have then been compression molded to form composite parts. Because of the high cost associated with these thermotropic liquid crystalline polymers and the desire to generate recyclable composites, a process was developed in this research to separate the liquid crystalline component from polypropylene (PP) composites. The overall objectives of this work were to develop a process to reclaim the liquid crystalline component of these thermoplastic composites, to determine the effect the process had on the properties of the reclaimed liquid crystalline polymer, and finally to determine whether or not the reclaimed liquid crystalline polymer could be used again to generate a reinforcing component. An ancillary objective was to see if the polypropylene could also be reclaimed, and if it had further use as a polymeric resin. In the present work, a novel process was developed that allows the liquid crystalline component to be reclaimed for further use in the composite material or in other applications that require thermotropic liquid crystalline polymers. The polypropylene component, which has undergone molecular weight reduction, can also be reclaimed by this process. This process consisted of using an organic peroxide and reactive extrusion to selectively degrade only the polypropylene, and not the thermotropic liquid crystalline polymer. The degraded polypropylene was selectively dissolved away from the liquid crystalline polymer by stirring the extruded melt in boiling mineral oil. The remaining solids, of thermotropic liquid crystalline polymer, were collected via centrifugation, cleaned of the mineral oil by boiling in kerosene, and then dried in a convection oven. The purity of the reclaimed thermotropic liquid crystalline polymer was determined by density measurements, while the physical properties of the reclaimed material were determined by rheological tests. The mechanical properties were determined via Instron testing of injection molded plaques made from mixtures of reclaimed material and pure thermotropic liquid crystalline polymer. From this work, it was found that over 70 wt% of the thermotropic liquid crystalline polymer, DuPont HX8000, could be successfully separated from the polypropylene to a degree of 96.0%. From Instron testing, it was found that up to 40 wt% of the reclaimed HX8000 could be blended with the pure HX8000, with no loss in mechanical properties. Furthermore, it was seen that up to 83 % of the HX8000 component (40 wt%) of PP 6523 (60 wt%) composites could be replaced with reclaimed HX8000 without seeing any losses in mechanical properties. It was also found that the degraded polypropylene could be successfully separated, via centrifugation at a temperature of 253 K, and could be potentially used as resin for non-wovens. The projected material cost of the reclaimed HX8000, based on the ability to purchase and to process in bulk, was determined to be 90 % less than the virgin HX8000. / Master of Science

Combining petrological and geochronological data we were able to show that rocks in south Naxos completed a full blueschist-/greenschist-facies metamorphic loop in about 10 Myr, distinctly faster than hitherto believed. We show that the high-pressure rocks reached peak pressure (16.3±0.9 kbar - 619 ±32°C) between 40.5±1.0 and 38.3±0.5 Ma and were re-equilibrated in the middle crust (3.8±1.1 kbar - 384±30 °C) under greenschist-facies metamorphism during in the Oligocene ~32 Ma. Our data indicate that this exhumation occurred at rates of 7.4±4.6 km Ma-1. Therefore, the Oligocene greenschist-facies overprint of the blueschist-facies rocks from south Naxos is unrelated to the Miocene amphibolite-/greenschist-facies metamorphism observed in Naxos. / Genom att kombinera petrologiska och geokronologiska data kan vi visa att bergarter på södra Naxos fullföljt en fullständig blåskiffer-/grönskiffer-facies metamorfisk loop på 10 Ma. Detta är mycket snabbare änn vad man tidigare trott. Vi visar att högtrycks bergarter nådde maximalt tryck (16.3±0.9 kbar - 619 ±32°C) mellan 40.5±1.0 och 38.3±0.5 Ma och var åter i jämnvikt i mitten av jordskorpan (3.8±1.1 kbar - 384±30 °C) under grönskiffer-facies metamorfism under Oligocen vid ~32 Ma.Våra data visar att exhumeringen skedde med hastigheter av 7.4±4.6 km Ma-1. Därför är den Oligocena grönskiffer-facies ersättningen av blåskiffer-facies på södra Naxos ej relaterad till den Miocena amfibolit-/grönskiffer-facies som observerats på Naxos. / En combinant les données pétrologiques et géochronologiques, nous avons été en mesure de montrer que les roches du Sud Naxos ont effectué un trajet complet en métamorphisme schiste bleue/schiste vert en 10 Ma, distinctement plus rapide que ce qui était admis jusqu’alors. Nous montrons que les roches de haute pression ont atteint un pic de pression (16.3±0.9 kbar - 619 ±32°C) entre 40.5±1.0 et 38.3±0.5 Ma et ont été rééquilibrées en croûte moyenne (3.8±1.1 kbar - 384±30 °C) en métamorphisme de facies schiste vert pendant l’Oligocène ~32 Ma. Nos données indiquent que cette exhumation a une vitesse de 7.4±4.6 km Ma-1. Par conséquent, la surimpression des roches de haute pression en métamorphisme de facies schiste vert dans le sud de Naxos n’est pas à relier au métamorphisme de facies amphibolite/schiste vert du Miocène observé à Naxos.

The origin of texture components associated with rare-earth (RE) element additions in wrought magnesium (Mg) alloys is a long-standing problem in magnesium technology. The objective of this research is to identify the mechanisms accountable for rare-earth texture during dynamic recrystallization (DRX). Towards this end, we designed binary Mg-Cerium and Mg-Gadolinium alloys along with complex alloy compositions containing zinc, yttrium and Mischmetal. Binary alloys along with pure Mg were designed to individually investigate their effects on texture evolutions, while complex compositions are designed to develop randomized texture, and be used in automotive and aerospace applications. We selected indirect extrusion to thermomechanically process our materials. Different extrusion ratios and speeds were designed to produce partially and fully recrystallized microstructures, allowing us to analyze DRX from its early stages to completion. X-ray diffraction, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to conduct microstructure and texture analyses Our analyses revealed that rare-earth elements in zinc-containing magnesium alloys promote discontinuous dynamic recrystallization at the grain boundaries. During nucleation, the effect of rare earth elements on orientation selection was explained by the concomitant actions of multiple Taylor axes in the same grain. Isotropic grain growth was observed due to rare earth elements segregating to grain boundaries, which lead to texture randomization. The nucleation in binary Mg-RE alloys took place by continuous formation of necklace structures. Stochastic relaxation of basal and non-basal dislocations into lowangle grain boundaries produced chains of embryos with nearly random orientations. Schmid factor analysis showed a lower net activation of dislocations in RE textured grains compared to ones on the other side of the stereographic triangle. Lower dislocation densities within RE grains favored their growth by setting the boundary migration direction toward grains with higher dislocation density, thereby decreasing the system energy. We investigated the influence of RE elements on extension twinning induced hardening. RE addition enhanced tensile twinning induced hardening significantly. EBSD analysis illustrated that tensile twins cross low angle grain boundaries in Mg-RE alloys, which produced large twins and facilitated transmutation of basal to prismatic dislocations. Higher activity of pyramidal II dislocations in Mg-RE alloys resulted in higher twinning induced hardening.

Paxymer AB is a company that manufactures and sells flame retardants for plastics, based on their patented technology. The flame retardants are often sold as a master-batch that the customers mix into their own plastic products. Paxymer has two master-batches with the exact same formulation, but are produced with different temperature profiles. The high temperature extrusion process produces pellets with good properties whereas the low temperature process do not. The aim of this study was to define what rheological properties are important in the extrusion process, and how they can be correlated to the pellet quality. The aim was also to predict the processing parameters for the low temperature extrusion process to improve the pellet quality. The rheological behavior of the two master-batches was investigated through analysis of the batches, as well as their additional components, in the rheometer. According to the results the viscosity of the melt is very temperature dependent, and were found to be significantly lower for the high temperature process. My studies show that the poor pellet quality in the low temperature process is most likely due to the high melt viscosity, which leads to poor mixing of the components. To get equal melt viscosity in the low temperature process as in the high temperature process, I found that the screw speed and feed rate in the extruder needs to be increased. According to my analysis the desired screw speed should be approximately 500 rpm if the temperature was increased with 10°C. To get the right viscosity at the die exit, the feed rate would need to be 20 kg/h. / Paxymer är ett företag som tillverkar och säljer flamskyddsmedel för plaster, baserad på deras patenterade teknik. Flamskyddsmedlet säljs oftast som en master-batch vilket kunderna blandar ner i deras egna plastmaterial. Paxymer har två master-batches med samma innehåll men som är tillverkade med olika temperaturprofiler. Tillverkningsprocessen med högre temperaturprofil producerar pellets med hög kvalitet och processen med lägre temperaturprofil gör inte det. Syftet med den här studien var att ta reda på vilka reologiska egenskaper som är betydande för framställningen av pellets med god kvalitet. Ett ytterligare syfte med projektet var att förutsäga extruderingsparametrar för processen med lägre temperatur för att uppnå en bättre kvalitet. De reologiska egenskaperna för båda master-batcherna och deras innehållande komponenter analyserades i en reometer. Enligt mina resultat så är plastsmältans viskositet väldigt temperaturberoende och visade sig därför vara betydligt lägre vid extruderingsprocessen med högre temperaturprofil. Den låga produktkvaliteten från processen med låg temperaturprofil beror sannolikt på att smältans viskositet var för hög, vilket leder till sämre blandning av komponenterna. För att få samma viskositet på smältan vid den lägre temperaturen i extrudern, som vid den högre temperaturen, så måste hastigheten på skruven samt inmatningshastigheten ökas. Enligt mina analyser så måste hastigheten på skruven ökas till 500 rpm om temperaturen även höjs med 10°C. För att få rätt viskositet i matrishålen så måste inmatningshastigheten öka till 20 kg/h.

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