No description available.

No description available.

No description available.

In recent years structured packings have become more widely used in the process industries because of their improved volumetric efficiency. Most structured packings consist of corrugated sheets placed in the vertical plane The corrugations provide a regular network of channels for vapour liquid contact. Until recently it has been necessary to develop new packings by trial and error, testing new shapes in the laboratory. The orderly repetitive nature of the channel network produced by a structured packing suggests it may be possible to develop improved structured packings by the application of computational fluid dynamics (CFD) to calculate the packing performance and evaluate changes in shape so as to reduce the need for laboratory testing. In this work the CFD package PHOENICS has been used to predict the flow patterns produced in the vapour phase as it passes through the channel network. A particular novelty of the approach is to set up a method of solving the Navier Stokes equations for any particular intersection of channels. The flow pattern of the streams leaving the intersection is then made the input to the downstream intersection. In this way the flow pattern within a section of packing can be calculated. The resulting heat or mass transfer performance can be calculated by other standard CFD procedures. The CFD predictions revealed a circulation developing within the channels which produce a loss in mass transfer efficiency The calculations explained and predicted a change in mass transfer efficiency with depth of the sheets. This effect was also shown experimentally. New shapes of packing were proposed to remove the circulation and these were evaluated using CFD. A new shape was chosen and manufactured. This was tested experimentally and found to have a higher mass transfer efficiency than the standard packing.

Plastics fuel tanks have been used successfully abroad ; metal counterparts are still predominant in this country plastics tanks have to satisfy stringent performance regulations : low temperature impact tests ; permeability ; and fire resistance. Blow moulded high density polyethylene (HDPE) fuel tanks have superior strength to mass ratio compared with metal equivalents (the density of steel is about 8000 kg/m3 compared with HDPE, which has a density of under 1000 kg/m3 ). HDPE will tend to drip in a fire situation, thus reducing explosion risk. HDPE is the chosen material because it possesses inherent properties suitable for the blow moulding process : it has a high viscosity at low stresses ; and is highly inert. Rotational moulded HDPE fuel tanks can also be considered. However, these are shown to have inferior properties when compared with blow moulded tanks ; attraction of rotational moulding is the cheapness of equipment. Petrol immersion was found to enhance impact properties of HDPE, although yield stresses were lowered slightly. The thickness distributions of blow moulded fuel tanks were found to vary ; this is because of the present difficulty of predicting parison behaviour with respect to time. Thickness is important because of impact strength and permeation considerations. Impact properties of fuel tanks were assessed ; peak force of impact was found to be heavily dependent on thickness (raised to the power 1.1) and temperature of mould in the blow moulding process (a low mould temperature led to inferior properties). Pinch-offs were found to be particularly detrimental to impact properties. Cooling behaviour was investigated. With the aid of a cooling model for blow mouldings, it was found that a warm mould (40·C) could be used with internal air circulation to obtain a cooling time the same as that with a cold mould and no air circulation. Thus optimising mechanical strength and maintaining economic viability. Welding of injection moulded fittings to the main blow moulded body of the fuel tank was found to be faulty, in all of the tanks examined ; many weld failures have been reported in use. This work determines optimum welding conditions for HDPE grades, these are Rigidex H060-45P and Lupolen 426l-A.

No description available.

No description available.

Nearly 60 m tonnes of waste is produced annually in Europe from “plastic packaging” engendering significant challenges for legislative controls and minimisation of environmental impact. There is an increasing demand for biodegradable packaging, which can be disposed of with minimum environmental impact, but the growing market is still in its infancy predominantly due to a lack of materials having environmental, practical and economic suitability. This research project dealt with some processing challenges of environmentally friendly packaging materials from renewable resources, as a long term solution to mitigate some issues associated with oil based plastic packaging. In this work, novel Polylactic acid (PLA) and starch based composites were developed with the requisite technical properties to fill the gap in the food packaging and cosmetic packaging industry. It was found that starch can be incorporated in a PLA matrix at the 10% level without difficulty in processing in the presence of 2% methyldiphenyl diisocyante. The blend shows properties similar to pure PLA. It was also found that the elongation at break and impact properties of PLA can be increased remarkably by the addition of a biostrength impact modifier. Furthermore, mixing of PLA and starch in the blend is efficient when the PLA particle size is reduced. It was also found that flexible and tougher PLA/starch blend pellets, that can be injection moulded, can be produced by an extrusion process with a range of additives. Each additive has a maximum level that exhibits optimum properties. The blends also established that 15% starch can be incorporated into the PLA matrix to reduce the cost without any processing difficulties. Encouragingly, the presence of an impact modifier in the PLA/starch blends has shown more desirable properties. Furthermore, the mechanical properties of the pellets exposed to increased residence time in the injection moulding barrel and of the test specimens stored for 9 months at 21ºC were also satisfactory for the new blend. The overall results exhibited some attractive properties in the tri blend system, which can be easily adopted by the plastics industry for development of an injection moulded product within the scope of applications such as dry food packaging or cosmetic packaging. A further finding of this project is that biodegradation under a home composting environment can be improved by incorporating starch and certain other modifiers into PLA.

In this study, commercially available isotactic polypropylene (PP) and nylon-6 (PA6) blends and laminates were prepared, to develop a material with optimal water vapour and oxygen barrier properties. The effect of compatibilizers on phase dispersion has been investigated using three commercial Polybond's, PB3002, PB1001, and PB3009. Three compatibilizers prepared in-house were also used as, maleic anhydride(MA) grafted on PP, MA and butyl methacrylate(BMA) co-polymer grafted on PP, and BMA grafted on low density polyethylene. The effect of two silanes( methacrylate functional and vinyl functional) on PP were also investigated and also the plasticization of PA6 with formic acid. The results were compared with a commercial blend of PP and PA6, Orgalloy R-6000. Light microscopy with phase and fluorescence contrast has been used for morphological evaluation. Chemical changes were studied by Fourier Transform Infrared Spectroscopy and rheology by dynamic and steady state measurements. Barrier properties were determined gravimetrically for water vapour and organic solvents, and for oxygen by an Oxtran apparatus. The results have shown that phase dispersion can be more easily explained by molecular interactions than by the rheological parameters. The blend slip factor has been improved however by compatibilizers and consequently the phase dispersion, which had little effect on the barrier properties of the blends and indeed the laminates were more effective water vapour barriers. The availability of particular functional groups, which can interact with the permeant is the most important parameter, which can be affected by processing and blending conditions. The addition of hydrophobic functional groups into polypropylene was therefore the most effective method for enhancing the barrier properties of polypropylene. Cross-linking of the matrix polymer has improved the barrier properties to a lesser extent. It has also been shown, that PP solvent permeability (particularly di-chloromethane) can be improved, by silane addition.

Ce travail s’inscrit dans le cadre du développement d’un procédé innovant de conditionnement de déchets nucléaires contenant des métaux contaminés en actinides. Le principe de ce procédé consiste à incorporer des concentrations élevées en actinides dans un bain de verre au contact de métaux fondus. Parmi eux, l’aluminium et/ou l’acier inoxydable imposent un environnement très réducteur et induisent des phénomènes d’oxydoréduction au sein du verre. Ces phénomènes provoquent un changement du degré d’oxydation des actinides qui modifie leur solubilité dans le verre et peut potentiellement entraîner leur réduction à l’état métallique. Afin de mieux comprendre les processus mis en jeu, cette étude va s’intéresser au comportement de l’uranium et de ses simulants à savoir l’hafnium et le néodyme, dans des verres aluminosilicatés du système Na2O-CaO-SiO2-Al2O3 et élaborés en conditions très réductrices. La première partie de ce manuscrit est consacrée à l’étude comparative des solubilités de l’uranium et de l’hafnium dans le verre en fonction des conditions redox et de la composition du verre. Pour cela, une méthodologie a été mise en place et un montage spécifique a été utilisé afin d’imposer la fugacité en oxygène et de contrôler la teneur en alcalins du verre. Les résultats indiquent que la solubilité de l’uranium dans le verre est très inférieure à celle de l’hafnium (HfIV) dans des conditions réductrices. Pour des fugacités en oxygène inférieures à 10-14 atm, la solubilité de l’uranium est comprise entre 4 et 7 % massiques d’UO2 dans la gamme de températures de 1250°C-1400°C. L’étude de la spéciation de l’uranium par spectroscopie d’absorption des rayons X (XANES) montre que l’uranium est majoritairement présent sous la forme UIV dans le verre pour de telles fugacités en oxygène imposées. Dans la seconde partie de ce travail, les mécanismes d’interactions verre-métal ont été identifiés afin de localiser l’uranium ainsi que ses simulants (néodyme et hafnium) dans le système verre-métal. Ces mécanismes sont principalement gouvernés par la présence d’aluminium métal et sont similaires pour l’uranium et ses simulants. Dans des conditions particulières, le suivi cinétique des expériences met en évidence la présence transitoire de l’uranium et de ses simulants à l’état métallique dans des alliages ou des composés définis. Au cours du temps, une ré-oxydation de ces éléments métalliques a lieu en accord avec les données thermodynamiques. Dans le cas de l’uranium, le processus de ré-oxydation reste à confirmer. Enfin, une approche thermodynamique à l’aide des diagrammes de phases a permis d’expliquer la formation et la dissolution des différentes phases cristallines présentes au sein du verre lors des interactions verre-métal / This study concerns an innovative process used for conditioning nuclear waste that contain metallic parts contaminated with actinides. High actinides concentrations are expected to be incorporated in the glass melt in contact with the molten metals. Among these metals, aluminum and/or stainless steel impose a strongly reducing environment to the glass melt involving redox reactions. These reactions modify actinides oxidation states and therefore change their solubilities in the glass and could also reduce them into the metallic form. In this work, we focus on the behavior of uranium and its surrogates, namely hafnium and neodymium, in aluminosilicate glasses from the Na2O-CaO-SiO2-Al2O3 system melted in highly reducing conditions. The first step consists in comparing the hafnium and uranium solubilities in the glass as functions of redox conditions and glass composition. A methodology has been set up and a specific device has been used to control the oxygen fugacity and the alkali content of the glass. The results show that uranium is far less soluble in the glass than hafnium (HfIV) in reducing conditions. The uranium solubility ranges from 4 to 7 wt% UO2 for an oxygen fugacity below 10-14 atm at 1250°C-1400°C. Uranium oxidation states have been investigated by X-ray absorption spectroscopy (XANES). It has been pointed out that UIV is the main form in the glass for such imposed oxygen fugacities. The second step of this work is to identify the glass-metal interaction mechanisms in order to determine the localization of uranium and its surrogates (Nd, Hf) in the glass-metal system. Mechanisms are mostly ruled by the presence of metallic aluminum and are similar for uranium, neodymium and hafnium. Glass-metal interaction kinetics demonstrate that uranium and its surrogates can temporarily be reduced into the metallic form for particular conditions. A re-oxidation occurs with time which is in good agreement with thermodynamics. Regarding uranium, the re-oxidation process must be corroborated. Finally, the formation and dissolution processes of the different crystalline phases observed during these glass-metal interactions have been studied using a thermodynamic approach based on phase diagrams