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The techno-economic implications of recycling the components of mixed plastics waste have been studied in a two-part investigation: (a) An economic survey of the prospects for plastics recycling, the plastics waste arisings from retailing, building, automotive, light engineering and chemical industries have been surveyed by mans of questionnaires and interviews. This was partially successful and indicated that very considerable quantities of relatively clean plastics packaging was available in major department chains and household stores. The possibility of devising collection systems for such sources, which do not lead to any extra cost, have been suggested. However, the household collection of plastics waste has been found to be uneconomic due to high cost of collection, transportation and lack of markets for the end products. (b) In a technical study of blends of PE/PP and PE/PS which are found in admixture in waste plastics, it has been shown that they exhibit poor mechanical properties due to incompatibility. Consequently reprocessing of such unsegregated blends results in products of little technological value. The inclusion of some commercial block and graft copolymers which behave as solid phase dispersants (SPES) increase the toughness of the blends (e.g. EPDM in PE/PP blend and SBS in PE/PS blend). Also, EPDM is found to be very effective for improving the toughness of single component polypropylene. However, the improved Technical properties of such blends have been accompanied by a fast rate of photo-oxidation and loss of toughness due to the presence of unsaturation in SPD's. The change in mechanical properties occurring during oven ageing and ultra-violet light accelerated weathering of these binary and ternary blends was followed by a viscoelastonetric technique (Rheovibron) over 9,, wide range of temperatures, impact resistance at room temperature (20-41'G) and changes in functional groups (i.e. carbonyl and trans-1,4-polybutadiene). Also the heat and light stability of single and mixed plastics to which thiol antioxidants were bound to SPE1 segment have been studied and compared with conventional antioxidants. The long-term performance of the mixed plastics containing SPE1 have been improved significantly by the use of conventional and bound antioxidants. It is concluded that an estimated amount of 30000 tonnes/year of plastics waste is available from department chains and household stores which can be converted to useful end products. This justifies pilot-experiments in collaboration with supermarkets, recyclers and converters by use of low cost SPD's and additives designed to make the materials more compatible.

Les polyoxométallates (POMs) sont des oxydes moléculaires anioniques de métaux de transition qui présentent une grande diversité de composition chimique et de structure. Ils possèdent également des propriétés redox et optiques spécifiques et peuvent être associés via des approches ionique et covalente à des molécules organiques photochromes et/ou photoluminescentes pour élaborer des matériaux hybrides organiques-inorganiques photoactifs. Ce couplage innovant permet de moduler ou exalter de manière drastique les propriétés photophysiques des molécules organiques à l'état solide et constitue une approche très prometteuse pour réaliser des dispositifs photoactifs efficaces. Dans une première partie, de nouveaux matériaux photocommutables ont été élaborés en combinant les POMs à un diaryléthène cationique ou en incorporant des entités POM-spiropyrane photochromes dans des matrices polymères. Dans une seconde partie, de nouveaux systèmes hybrides luminescents ont été conçus en assemblant les POMs avec un complexe cyclométallé d’iridium (III) phosphorescent ou un phospholium fluorescent présentant des propriétés d’exaltation d’émission par agrégation. Pour finir, une troisième partie recense différentes stratégies d’assemblage visant à développer des matériaux multifonctionnels à base de POMs, couplant photochromisme et luminescence. Parmi elles, une nouvelle approche a notamment été explorée pour développer des assemblages supramoléculaires qui combinent des POMs intrinsèquement luminescents à base de lanthanides avec des molécules organiques photochromes. / Polyoxometalates (POMs) are anionic molecular oxides building blocks of transition metals which exhibit a wide variety of chemical composition and structure. They also possess specific redox and optical properties and they can be combined via ionic and covalent approaches to photochromic and/or photoluminescent organic molecules to design new photoactive hybrid organic-inorganic materials. This innovating coupling is an attractive opportunity to drastically tune or improve the photophysical properties of organic molecules in the solid-state and it constitutes a promising approach for the elaboration of efficient photoadressable devices. In a first part, new photoswitchable materials have been developped by combining POMs with a cationic diarylethene or by incorporating photochromic POM-spiropyran entities into polymeric matrices. In a second part, new luminescent hybrid systems were designed by assembling POMs with a phosphorescent iridium (III) complex or a fluorescent phospholium which shows Aggregation-Induced Emission (AIE) properties. Finally, a third part identifies different assembly strategies to develop multifunctional POM materials, coupling photochromism and photoluminescence. Among them, a new approach has been explored in particular to develop supramolecular assemblies that combine intrinsically luminescent POMs incorporating lanthanide cation with photochromic organic molecules.

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A literature survey of the properties and uses of high strength concrete, defined for this study as having a strength in excess of 60 N/tnm2, has shown that of prime need is a systematic, reproducible procedure for attaining high strength concrete. The "Maximum Density Theory", i.e. the requirement that the aggregate occupies as large a relative volume as possible, has been adopted as an approach to optimisation of the mix proportions. However, this does not consider the effect that the aggregate suIface area has on the requirement of excess paste for lubrication. To investigate the combined effect of void content and surface area, mixes with lower sand proportions than that required for minimum void content were tested for slump. The optimum sand proportion is the one that produces the highest slump, for a particular cement content. This procedure has been called: "The Modified Maximum Density Theory". Having thus optimised the cement and aggregate contents, partial cement replacement by mineral admixtures, at low water-cement ratios, has been investigated in order to assess: a) their contribution to long term strengths, b) their contribution to reducing the heat evolution of concrete mixes, and c) their effect on the workability of concrete. Condensed silica fume (at replacement levels of up to 15%) produced higher compressive strengths than ordinary Portland cement. Ground granulated blast furnace slag (at replacement levels of up to 30%) can be used without decreasing the 28-day strength. Replacement by 20% pulverised fuel ash resulted in a 15% decrease in the 28-day strength and equal strength to ordinary Portland cement concrete at ages beyond 56-days. Temperature measurements during hydration, under adiabatic conditions, have however shown that these replacement levels do not lower the temperature rise at a water-binder ratio of 0.26. The higher levels required for significant temperature reduction will also cause a significant reduction in the strength. To offset this ground granulated blast furnace slag (58%) and pulverised fuel ash (36%) in combination with 10% condensed silica fume 4 were used. These combinations reduced the temperature rise by more than 10°C while the reduction in the 28-day compressive strength was less than 15%. Partial cement replacement by pulverised fuel ash and ground granulated blast furnace slag improved the workability and therefore allowed a reduction in the superplasticiser dosage required for a given slump. The use of condensed silica fume reduces the workability at low superplasticiser dosages, but it has a water-reducing effect above a certain superplasticiser dosage. Results from these studies have been used to formulate guidelines for the proportioning of materials for producing high strength concrete.

The work presented in this thesis is concerned with the adsorption of silver from aqueous solution, on soda-glass, polyethylene and polypropylene. The silver concentrations used, ranged from 0.5 to 100 mg dm-3, and were investigated at a series of temperatures. The silver was present as AnalaR silver nitrate in doubly deionised water, and the adsorbed silver was detected as silver -110m using a Nal(Tl) well-type crystal to count the gamma activity. The study indicates that silver adsorption on glass is extremely pH sensitive, increasing with increasing pH, and reaching a maximum value at pH 11.5. At pH values greater than 11.5 silver adsorption is significantly reduced. The pH dependence was shown to be important at silver concentrations ranging from 0.5 to 100 mg dm-3. The presence of added cations, other than the hydrogen ion, also inhibit the adsorption of silver. The pH work was extended to include desorption under acid conditions, and the results have been used to formulate a set of guidelines, in an attempt to improve existing analytical technique when handling trace concentrations of silver. A contact-time study was carried out at various temperatures and concentrations of silver, to establish a tentative equilibrium time for the adsorption process. A kinetic analysis has been applied, from which specific rates for the forward and reverse processes have been assigned. The effect of pH and concentration on these rates has also been considered. The temperature dependence of silver adsorption was investigated, and a series of isotherms were produced at 281, 293, 298 and 303 K. The isotherms indicate a positive temperature coefficient for the adsorption of silver on glass. A thermodynamic treatment was applied, and a heat of adsorption calculated. A possible mechanism for the adsorption of silver on soda-glass has been proposed. The work was extended to investigate the adsorption of silver on substrates apart from glass, namely, polyethylene and polypropylene. The results have been compared to those obtained for glass.

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