Gas sensors based on different principles have been developed for the applications of environmental monitoring, industrial processing, aerospace and the human body. Carbon nanotubes (CNTs) demonstrate a detectable electrical properties change upon gas molecules absorption. This has been extensively studied and used in chemiresistors and chemical field-effect transistors. Simultaneous response to different types of gases was reported. The aim of this study is to develop a new type of gas sensor by replacing the gate metal of a field-effect capacitor with a carbon nanotubes network. This novel sensor will combine resistivity measurements with potentiometric measurements, which should ideally lead to increased functionality and selectivity. The substrates (Al/Si/SiO2/Si3N4 or Al/Si/SiO2/Si3N4/LaF3) were fabricated with two gate electrode structures (interdigitated and two-line). CNTs in different solvents were drop or spray coated on to the substrates. Platinum coating on the CNTs was also introduced. The resistive measurements indicated an increase in the resistance of CNTs networks with increased oxygen concentration, and a decrease in the resistance of CNTs networks with increased hydrogen concentration with humidity interference. Evenly distributed CNTs film was achieved by spray coating which allowed the use of CNTs network as gate materials for potentiometric measurements. The potentiometric measurements suggested that the C-V curve shifted towards a lower voltage with an increased hydrogen concentration, and a higher voltage with an increased oxygen concentration. However, the response time was too long for practical applications. Pt deposition significantly improved the hydrogen response rate. A voltage shift of -450 mV with an equilibration time of 2 minutes was achieved when the hydrogen concentration increased from 1 to 100%. The C-V curve shifted by 500 mV with increased oxygen concentration (1-100%).

The aim of this project was two-fold. Firstly to provide an understanding of the behaviour of SMC when subjected to drop weight impact and secondly to investigate the effect of a surface layer of a metallic material (stainless steel, aluminium, brass and copper) and a layer of Ionomer on the impact behaviour of SMC. Tensile, flexural, compression, shear, charpy and drop weight impact tests were carried out on SMC (Sheet Moulding Compound). The response of SMC and various combinations of SMC and metal sheet (stainless steel, aluminium, brass and copper) and SMC with a layer of Ionomer to impact load have been assessed using an Instrumented Falling Weight Impact test machine. Slow indentation tests and a variety of destructive and non-destructive test techniques were used to monitor the initiation and propagation of damage and relate them to the major features of typical force-time curves obtained during impact. The deformation of the metallic layer was compared under impact and slow test and a calibration curve was produced. By using the calibration curve the energy absorbed by SMC and SMC as a layer in SMC+metal laminate was compared and results were related to stiffness and ductility of the metallic layer. The energy absorbed by the SMC-metal laminates were analysed and the energy absorbed by each constituents was determined. The effect of impact damage on tensile and compressive residual strength was assessed by conducting tension and compression test on the damaged specimens. Finally, a number of simple models and fInite element technique were used to predict the impact response of SMC and SMCmetal laminates to impact. The results of the research programme indicated a strong macrocomposite effect resulting in greatly improved energy absorbing capabilities for SMC. The indications were that a metal layer was required that would be stiff, thereby putting the SMC into compression and also ductile in order to support extensive deformation in the SMC whereby microcracking could accumulate.

Isotropic polymers lack sufficient strength and stiffness for many engineering applications. In order to improve these properties polymers can be filled with structural reinforcements such as glass or natural fibres. However, current major trends focus on simple monocomponent systems in an effort to reduce costs and increase recyclability. Composite systems, by definition, must employ at least two phases with different material properties. With the introduction of careful processing routes, it has been proven possible to create a fibrous, two phase composite, in which both are polypropylene. Polypropylene can be melt spun and solid state drawn to give oriented tapes, and moduli of -15GPa and tensile strengths of -550MPa can be achieved. These tapes can then be oriented into sheets, either in the form of woven fabrics or unidirectional layers. These sheets form the reinforcing phase of a single polymer composite material. Such single polymer composites based on polyolefins can be produced by using a separate matrix impregnation route, but these are limited by relatively low volume fractions of reinforcement. Previous work executed at the University of Leeds showed that polymer fibres can be welded together by selective melting of the fibre exterior, but this method is limited by a small temperature processing window. By using polypropylene tapes co-extruded with a copolymer skin, it has been shown that such tapes can be welded together at temperatures far below the melting temperature of the tapes, thus ensuring that thermal relaxation of the highly oriented polymer does not occur. The temperature processing window can be widened further by constraining fibres during heating. The optimisation of the drawing and structure of these tapes, together with an investigation of the static and dynamic mechanical properties, impact resistance and interfacial properties of composites formed from these tapes, are investigated in this thesis

In the construction industry, prepainted metal strip is a widely used material for fagade and roofs of building intended for commercial used. The physical properties of modem coatings are outstanding, however one big problem that remains and which affects the overall coatings performance is dirt pick up. Firstly the effect of weathering induced chemical composition change was evaluated using photo-acoustic infrared spectroscopy (PA-FTIR), and X-ray photoelectron spectroscopy (XPS). The results shown that photo-oxidation processes occurs via Norrish type I and type 11 reaction at several sites on the polymer backbone, with the ester linkage and the melamine crosslinkage being the more reactive. Secondly aluminosilicates have been found to be the main source of soiling with organic pollutants also responsible but to a minor extent, the presence of such dirt was confirmed by XPS analyses. Unusual peak shape was observed on the carbon narrow scans with low binding photoelectron emitted. Finally Polymer/organically modified layered silicates (PLS) nanocomposites are a new class of filled polymer with ultrafine phase dimension. They improve considerably the physical properties of the coating while reducing dirt pick up. The best results were obtained when the insitu intercalative method was used. However the implication of the onium salts is obscure and the relation between the nanocomposite structure and its properties is not well understood.

Porous scaffold materials have been widely used in biological tissue engineering. It is known that fluid flow in porous media significantly increases the supply of oxygen and other nutrients to cells seeded in the porous material, and speeds up the clearance of metabolic end products. Local shear stress distribution is a function of media flow rate, viscosity and the porous scaffold micro-structure. This research project aims to investigate fluid movement in porous structures by using a lattice Boltzmann method. This new numerical method models the fluid as a collection of identical particles with collision and propagation procedures, and has been shown as an alternative and efficient numerical solver of Navier-Stokes equations, in particular for flows in complex geometries. The numerical scheme is verified using flow in a two-dimensional channel, as well as in three-dimensional ducts with constant shapes, where analytical solutions are available. 2D porous structures originated from micro-CT images are then used to study the flow and wall shear stress distribution. One of the advantages of the lattice Boltzmann method is that the shear stress can be computed directly from the local distribution function and has the same accuracy with the velocity profile. Fluid patterns and wall shear stress distribution in 3D porous structures, which 6 are reconstructed from the micro-tomographic slices, have been investigated under different flow rates, viscosity and geometrical structures. Results from this project demonstrate that lattice Boltzmann method is suitable for flow modelling in scaffold materials. It provides detailed information on localized velocity and stress distributions, which can be used to improve the design of the scaffold for cell and tissue engineering.

Ceramic materials have considerable attraction for use in applications where the service temperatures are high and where fire performance and non-combustibility are important. Unfortunately most monolithic ceramic materials are extremely brittle which limits their use for structural applications. The development of fibre and particulate reinforced ceramic composites provides a route to achieving increased toughness in the materials, although this is often at the expense of ultimate strengths and/or the process-ability of the materials. Many reinforcing fibres used with ceramics are inherently expensive and manufacturing routes to produce fibre reinforced materials can involve high processing temperatures and are consequently expensive. A key goal of this research therefore is to develop a new type of ceramic matrix composites that combine toughness, strength and process-ability to provide a cost effective structural material. The research described in this thesis has been concerned with the development and characterisation of a series of ceramic compounds that can be moulded at modest temperatures( 130-160" C) and pressures in a manufacturing system that replicates dough moulding compounds (DMC) as used for polymeric matrix composites. The conventional polyester matrix of polymeric DMC has been replaced by a soluble inorganic system which is compounded with fibres, fillers and hardening agents to produce a paste-like or doughy substance The handle-ability of the material is determined by the viscosity of the matrix and the type or amount of fillers and additives present. The research has involved a careful set of experiments in which the formulation of the ceramic DMC has been systematically varied in order to achieve an optimum viscosity for storage and handling together with a further series of experiments studying the hardening and cure of the compounds. The mechanical properties of the compounds have been measured and additional formulation changes have been introduced to maintain desirable processing characteristics while improving mechanical properties, and in particular the impact resistance using instrumented falling weight impact machines. Finally the fire properties of the compounds have been studied using cone calorimetry and indicative furnace testing. The structure of the compound has been studied throughout the programme with various microscopic techniques and thermal analysis systems used to characterise the materials, their dispersion and changes that occurred during processing and after high temperature exposure. The final result of the programme has been the identification of a range of material formulations that can provide a tough moulding compound, capable of high temperature service use, that possesses useful structural properties and which can be processed cheaply at modest temperatures using low cost materials.

Composites are normally composed of two distinct phases: reinforcement and matrix. In recent years, a new class of “self-reinforced” polymer composites or “all-polymer” composites, which are based on similar or identical materials for both reinforcement and matrix have generated increasing interests in both academia and industries due to their advantages in terms of processing, interfacial properties and recyclability. Current research trend in this field is to investigate the potential possibilities of all-polymer composites based on high-performance polymer fibres. In this thesis, all-poly(ethylene terephthalate) composites (Part 1) and all-aramid composites (Part 2) were prepared. In Part 1, Chapter 3 describes the melt spinning and drawing of poly(ethylene terephthalate) (PET) into highly oriented fibres, with moduli of 20GPa and tensile strengths of 925MPa. The effects of spinning and drawing conditions on the mechanical properties of PET fibres were studied. In the following Chapters 4 and 5, all-PET composites were prepared from 1) hot compaction of bi-component multifilament PET yarns; and 2) a film stacking technique, i.e. combining PET tapes unidirectionally with copolyester adhesive films in an alternating “brick-wall” layer-by-layer structure. The effects of processing conditions on mechanical properties were investigated. In Part 2 Chapter 7, all-aramid composites were prepared by a selective surface dissolution method where aramid fibres were partially dissolved to form a matrix phase to bond remaining fibres together into composites. The structure, morphology and mechanical properties were characterized by X-ray diffraction, scanning electronic microscopy, dynamic mechanical analysis and tensile testing. Compared to traditional aramid/epoxy composites, these all-aramid composites show significantly high mechanical properties, even at elevated temperatures. In Chapter 8, the effects of processing conditions on various properties of all-aramid composites were studied and an optimum condition was found. By replacing high concentration sulphuric acid as a solvent, a mild mixed solvent was used to dissolve aramid fibre surfaces in Chapter 9. In this way, all-aramid composites with prolonged immersion times were prepared and characterized. Potential future work including all-PET composites from post-consumer PET waste, microstructural characterization of all-aramid composites and woven all-aramid composites are discussed in Chapter 10.

It is desirable for a dental restorative material to have bioactive and bonding properties. This study focuses on the synthesis of a covalently-linked polyurethane/nanohydroxyapatite (PU/nHA) composite and evaluates its chemical, physical, thermal and biochemical characteristics. nHA powder was produced from the sol-gel and novel composite material was chemically prepared by utilising solvent polymerisation. The resulting composites were analysed by chemical, thermal, and mechanical characterisations and electrospun to form fibre mats. The composites were hydrolytically degraded in deionised water and phosphate buffer solution (PBS) and were analysed. Bioactive behaviour was determined in modified-simulated body fluid. The bioadhesion with dentine was analysed in distilled water and artificial saliva. Cell growth and proliferation was measured and number of adhering bacteria was determined and serial dilution followed by plating for colony forming units per disc. Spectral analyses showed the grafted isocyanate and ether peaks on nHA indicating that urethane linkage was established. Covalent-linkage between nHA and PU were found in this novel composite with no silane agent. The physical and thermal properties were enhanced by nHA. These composites had high resistance toward hydrolysis and little degradation was observed. Bioadhesion and bioactivity analysis showed the composite adhered firmly on the tooth surface (dentine) and bond strength was similar to existing obturating material. Higher nHA content composite showed a thicker layer of adhesion. Cells were proliferated although at a lower rate of growth compared to PU, whereas, there was reduction in bacteria adhering to the grafted composite compared to PU. With its low bacterial adhesion and biocompatibility it may provide a promising solution to reduce infections. The electrospun nano-fibres were successfully developed and revealed no loose nHA particles. Hence, this novel composite has the potential to be used as a bioactive dental restorative material.

Considerable effort has been devoted to the M-N-H system for solid-state hydrogen storage. However, the desorption mechanism is still unclear and the desorption temperature is too high for practical considerations. Here, the desorption characteristics of LiNH2 and a mixture of (LiNH2+LiH) were firstly comparatively studied by simultaneous then-nogravimetry, differential scanning calorimetry and mass spectrometry for further understanding of H2 desorption in the (LiNH2+LiH) system. Mass spectrometry and thermal analysis of (LiNH2+LiH) mixtures indicate that approximately 5 mass % of H2 is released at 180*C after four hours of milling without any apparent release of NH3, whereas insufficient mixing of the two compounds cannot stop the escaping of NH3 from the mixture. Non-unifon-ri mixing can lead to the escape of NH3 from the mixture. The evidence further supports the notion that NH3 intermediated reaction is a possible reaction path within the thermal desorption of the (LiNH2+ LiH) mixture. BN additive, among selected nitrides shows the best effect on desorption from (LiNH2+ LiH). (LiNH2+MgH2)materials with different molar ratios (4: 3,4: 2 and 4: 1) were also studied for their sorption properties and mechanisms. Results show that more than 6 mass% H2 is desorbed from 1500C for the (4LiNH2 +3MgH2)mixture, with two H2peaks at 200 and 320'C. Meanwhile, there is only -5 mass% for (4LiNH2 +2MgH2) mixture with one H2 peak at 200 T. Reversibility measurements suggest that LiNH2 and MgH2 cannot be recovered after absorption; instead, Li2NH and Mg(NH2)2 (or MgNH) take over to perform the H2 storage functions. The (4LiNH2+3MgH2 ) mixture possess a greater H2 capacity in first desorption, but shows less than 2 mass% reversible capacity in subsequent cycles. However, there is only about I mass% capacity loss during the reversibility measurement for the (4LiNH2 +2MgH2)mixture. Other M-N-H systems, mainly NaH, KH, AlH3 and CaH2, were also investigated, and only CaH2 shows the capability of reacting with LiNH2 to produce H2 among these candidates.

Since the discovery of carbon nanotubes (CNTs) and nanoclays, there has been a great deal of research conducted for uses in applications such as: energy storage, molecular electronics, structural composites, biomedical to name but a few. Owing to their unique intrinsic properties and size means that they have an ever growing potential in the consumer and high technology sectors. In recent years the concept of using these as fillers in polymers has shown great potential. One such function is, as flame retardant additives. These possess much better environmental credentials than halogenated based additives as well as only needing to use a small loading content compared to traditional micron sized fillers. The combination of the above make these fillers ideal candidates for polymers and their composites. Especially with regards to natural fibre composites. Owing to environmental awareness and economical considerations, natural fibre reinforced polymer composites seem to present a viable alternative to synthetic fibre reinforced polymer composites such as glass fibres. However, merely substituting synthetic with natural fibres only solves part of the problem. Therefore selecting a suitable material for the matrix is key. Cellulose is both the most common biopolymer and the most common organic compound on Earth. About 33 % of all plant matter is cellulose; i.e. the cellulose content of cotton is 90 % and that of wood is 50 %. However just like their synthetic counterparts, the poor flame retardancy of bio-derived versions restricts its application and development in important fields such as construction and transportation. Abstract -vi- Traditional methods to improve the flame retardancy of polymeric material involve the use of the micron sized inorganic fillers like ammonium polyphosphate (APP) or aluminium trihydroxide (ATH). Imparting flame retardancy with these inorganic fillers is possible but only with relatively high loadings of more than 50 wt. %. This causes detrimental effects to the mechanical properties of the composite and embrittlement. Applying nanofillers can achieve similar if not better flame retarding performances to their micron sized counterparts but at much lower loading levels (<10 wt.%), thus preserving better the characteristics of the unfilled polymer such as good flow, toughness, surface finish and low density. This is the main focus of this study and it will be achieved by using various experimental techniques including the cone calorimeter and the newly developed microcalorimeter. After a comprehensive literature survey (Chapter 2), the experimental part of the thesis starts with a feasibility study of a flame retardant natural reinforced fibre sheet moulding compound (SMC) (Chapter 3). This work demonstrated that with a suitable flame retardant the peak heat release rate can be reduced. Chapter 4 deals with further improving the flame retardancy of the previously used unsaturated polyester resin. The aim is to study any synergistic behaviour by using aluminium trihydroxide in conjunction with ammonium polyphosphate whilst testing in the cone calorimeter. In Chapter 5, nanofillers are used to replace traditional micron sized fillers. In unsaturated polyester, multi-walled carbon nanotubes and sepiolite nanoclay are used together to create a ternary polymer nanocomposite. The microcalorimeter was employed for screening of the heat release rate. This work showed that the ternary nanocomposite showed synergistic behaviour with regards to significantly reducing the peak heat release rate. Abstract -vii- The same nanofillers were utilised in Chapters 6 and 7 but this time in combination with a thermoplastic (polypropylene) and bio-derived polymer (polylactic acid), respectively. In both systems an improved flame retardancy behavior was achieved whist meeting the recyclability objective. Chapter 8 attempts to show how the optimised natural fibre composite would behaviour in a large scale fire test. The ConeTools software package was used to simulate the single burning item test (SBI) and to classify the end product. This is a necessity with regards to commercialising the product for consumer usage. Finally, Chapter 9 is a summary of the work carried out in this research as well as possible future work that should be conducted.