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.

Current and future structural applications for composite laminates frequently involve design solutions combining composite laminates and metal; the materials must be joined. Two conventional means of joining are available: mechanical joining and adhesive bonding. Both methods have critical disadvantages. A novel surface treatment for metals developed at TWI, Surfi-Sculpt™ leads to the formation of surface protrusions on metal surfaces. These protrusions are typically 1.0 mm high and 0.6 mm diameter. The surface modified metal can be bonded with composite laminates to form a Comeld™ joint. These joints can be described as a combination of mechanical fastening and adhesive bonding. There are many possible variables which could be applied to the metal surface. The variables include the shape, height, orientation and distribution (distribution pattern and density) of the protrusions. The aim of this work was to optimise the protrusions with respect to their geometry and distribution using the finite element modelling method for the Comeld™ joint under tensile loading with titanium alloy and cross-ply carbon prepreg composites. The simulations require multi-scale modelling techniques to transfer results between the global model, which is the reflection of the whole joint, and the unit cell models containing a protrusion. The two-dimensional simulations focused on the protrusion geometric parameters whereas the three-dimensional simulations focused on the protrusion spatial arrangement including the distribution pattern and density. Modelling of the entire joint geometry with two and three-dimensional global models was carried out using smeared properties for the adhesive layer which includes the protrusions. These models yield results for both quasi-static properties and stress distributions for these joints. Results from the simulations show critical effects on stress distributions arising from changing protrusion geometry. These joints show significant advantages over conventional joining technologies and their application would allow improved performance for combinations of metal and composite laminates.

A unique organic/inorganic nanocomposite of lead sulphide (PbS) quantum dots (QDs) embedded in substituted metal-free phthalocyanine (C6H2Pc) has been prepared by a simple and low-cost method. The preparation procedure consists of exposure of a thin spun film of non-peripherally octa-hexyl lead phthalocyanine to hydrogen sulphide atmosphere. The formation of the PbS QDs has been verified using X-ray diffraction and transmission electron microscopy techniques. From the transmission electron microscopic measurements, the average size of the PbS QDs is found to be 4.5 nm, which is smaller than the exciton Bohr radius. Independent Xray diffraction and optical absorption studies provide supportive evidence for the size of QDs. Quantum confinement gives rise to a clear blue shift in the absorption spectrum with respect to the bulk PbS. The QDs band gap has been estimated to be 1.95 eV from Tauc's law and the frontier energy levels of the PbS QDs has been derived. About two orders of magnitude increase in ohmic conductivity, from 6.0×10−12 for C6H2Pc to 3.1×10−10 for the nanocomposite, is observed by steady-state electrical measurements in sandwich structure between indium tin oxide and aluminium. Temperature-dependence of the electrical conduction is studied aimed to calculate the activation energy and determine the type of conductivity. The incorporation of the PbS QDs decreases the activation energy by about 0.5 eV at temperatures higher than 240 K. It is found that the Poole-Frenkel mechanism is in good consistency with the superlinear electrical behaviour of the nanocomposite. The frequency response of alternating current (AC) conduction is found to obey the universal power-law. The cryogenic study of AC conduction reveals that the correlated barrier hopping (CBH) model closely fits to the experimental data at temperatures below 240 K. The parameters obtained by fitting the CBH model point out that the hopping process cannot take place directly between neighbouring PbS QDs but involves the localised states within the matrix.

Globally, heart valve dysfunction constitutes a large portion of the cardiovascular disease load, causing high rates of mortality in European and industrialized countries. This is reflected in the database of the American Heart Association and the UK Valve Registry, showing a progressive increase in the number and age of patients in need of surgical interventions. Aortic valve (AV) dysfunction is significantly more prevalent than pathologies associated with other heart valves, accounting for approximately 43% of all patients having valvular disease. These statistics highlight the essential need for efficient and long term substitutes. However, the two types of replacement valves currently available in practice, i.e. mechanical and bioprosthetic valves, have only an estimated lifetime of around 10 years, after which the associated problems necessitate re-operation in at least 50-60% of the patients. Moreover, for patients under 35, the failure rate is nearly 100% within 5 years of the valve replacement surgery. The significant numbers of patients suffering from AV dysfunction, shortcomings to currently available valve substitutes, and the market demands for replacement valves has prompted increasing interest in the study of AV biomechanics. A fundamental study of the AV structure-function biomechanics is presented in this thesis. The mechanical behaviour of the AV is characterised at the tissue level, and the associated microstructural mechanisms established. In addition to the experiments, in depth mathematical models are developed and presented, to explain the observed experimental data and elucidate the micromechanics of the AV constituents and their contribution to the tissue behaviour. Tissue-level results indicate that the AV shows ‘shear-thinning’ behaviour, as well as anisotropic time-dependent characteristics. The microstructural experimental data indicates that there is no direct translation of tissue level mechanical stimuli to the ECM, implying that strain transfer is non-affine. Modelling micro-structural mechanics has confirmed that collagen fibres do not need to become fully straight before they contribute to load bearing, while the elastin network has been shown to contribute to load bearing even at high strains, further exacerbating the non-linear stress-strain relationship of the valve. The structural mechanisms underlying time-dependent behaviour of the tissue can be explained at the fibre level, stemming from fibre sliding and the dissipative effects arising due to fibre-fibre and fibre-matrix frictional interactions, suggesting a unified structural mechanism for both the stress-relaxation and creep phenomena. These outcomes contribute to an improved understanding of the physiological biomechanics of the native AV, and may therefore assist in optimising the design processes for substitute valves and selecting appropriate materials to effectively mimic the native valve function. Understanding AV micromechanics also helps quantify the mechanical environment perceived by the residing cells, which can have significant implications for cell-mediated tissue engineering strategies.

Microfluidic membranes are used in myriad applications, including use in microbioreactors. They serve as bio-catalyst surfaces or allow cell adhesion. However, creating such membranes requires complex manufacturing processes including multi-step self assemble. Recently, a nylon membrane was produced in situ in a flow channel [17]. This process is completed rapidly (within a few minutes), but such membranes are essentially only gas permeable. Control of the thickness and inclusion of porosity is important for effective membrane permeably for general solute transfer and could be sensitive for a given size range of molecules. In the present work, a simplified in situ fabrication technique has been used to produce a robust and novel protein micro-membrane. The proteins studied were BSA and fibrinogen with an acyl chloride to achieve protein crosslinking. Three acyl chloride crosslinkers were tested each crosslinker also generated unique surface morphologies and cross section morphological structures. Permeability of these membranes was tested by diffusion studies using dye molecules as well as the electrochemically active. A simplified approach of using ethanol to further modify the porosity of the membrane was established. Antibacterial membranes were achieved by exposing the protein membranes to copper sulphate solution. Tensile tests on the membranes showed that there was variation in membrane strength that was related to the crosslink or molecule type, and was also related to porosity.

In general, it is expected that concrete structures using Glass Fibre Reinforced Plastic (GFRP) rebars as reinforcement could have improved durability compared to normal steel reinforcement because of the corrosion resistance of the rebar. However, there are some aspects of the behaviour of the GFRP bars under high temperature that must be explored. The aims of this work are to predict the fire rating of the GFRP rebars when embedded in concrete elements by creating a model and to validate the model by full-scale experiments. The first part of this work evaluates the effects of alkaline environments on the rebar itself, the bond strength at interface between the concrete and the rebar, and the strength of the GFRP rebars at a range of different temperatures (20-120°C). The three types of GFRP rods investigated in this work were subjected to alkaline solutions at 60°C for three different exposure times i. e. 30 days, 120 days and 240 days. Tensile and flexural tests were carried out for the physico-mechanical characterisation on the treated GFRP rebars specimens. As the immersion period and temperature increased, the strength of the rebars decreased. Data obtained from the first part of the work were used to predict long-term performance of the GFRP rebar in fire. The effects of higher temperatures with time on GFRP reinforced concrete members were also studied experimentally in this work. As a result equations were developed. These were validated with the help of the fire tests carried out in second phase of this work on two full-scale GFRP reinforced concrete beams. The first beam was reinforced with GFRP made from thermoset resin and in the second GFRP made from thermoplastic resin was used. Shear reinforcement for the first beam were GFRP stirrups and for the second beam steel stirrups were used. Degradation of flexural and shear capacities due to fire was evaluated using the modified design codes which is based on assessment of the reduction in the initial strengths of concrete and GFRP reinforcement, resulting from the high temperatures developed inside the beam. A comparison of the results for each beam is presented. Fire resistance (load bearing capacity) of GFRP RC beams complied with British Standard BS 478. These results are published for the first time in this work. The predicted failure time using the model compares well with the fire test results. The 3 result also indicated that the basic fire model needed adjustment mainly due to a difference in the assumed and observed failure modes. The importance of data necessary for a more accurate model has been identified as a programme for future work.

A study has been made of the Instrumented Falling Weight Impact Test, investigating and analysing the effect of test parameters and specimen geometry on the characteristic results of the test. Two materials, poly(methylmethacrylate) and high density polyethylene are chosen, which exhibit typical extremes of brittle or ductile behaviour. High speed photography is used to monitor the development of deformation and progress of failure during the impact test. The major features of typical force-time curves obtained from the tests on PMMJL and HDPE are thus characterised in terms of failure development and quantified. Analyses are adopted which enable materials property data, such as modulus, E , fracture or yield stress, [Sigma][Subscript] f , [Sigma] [Subscript] y and a fracture parameter, G [Subscript] c to be obtained from the tests conducted on flat plates. A framework is proposed which would enable extraction of similar materials data from a wide range of plastics during routine testing with the falling weight test method.

A systematic investigation of the structural stability, evolution and hydrogenstorage properties of Mg-based hydrides was carried out, involving mechanical milling and chemical alloying. The effects of milling on particle size, lattice parameter, microstructure, and phase composition of the powder mixtures were characterised using SEM, X-Ray diffraction and quantitative Rietveld analyses. Mechanical milling was shown to be an effective method of refining the particle size, particularly when MgH2 is involved. The influences of the selected chemical elements, including transition metals, graphite carbon and rare-earth metals, on hydrogen desorption/absorption of various milled mixtures were clearly identified using coupled Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC). The as-received MgH2 shows an onset desorption temperature of 420°C. Mechanical milling reduces the onset temperature to 330°C. Chemical alloying, via surface catalysis and/or solid-solutioning, further increases the desorption kinetics and reduces the desorption temperature down to 250°C. The degree of such effect decreases from Ni, Al, Fe, Nb, Ti, to Cu. Further comparison of desorption characteristics of MgH2 mixed and mechanically alloyed with Ni clearly shows that the kinetic improvement and the effective reduction of the desorption temperature is mainly due to a catalytic effect, rather than solid-solutioning of Ni. Although posing little influence on desorption characteristics, graphite improves the absorption behaviour of MgH2. The rare earth metals, Y and Ce, do not seem to influence hydrogen desorption of MgH2 due to the formation of stable hydride phases, but CeO2 in the (MgH2+Ce) mixture provides a beneficial effect on desorption kinetics. Multi-component mixtures of (MgH2+15Fe+5Ce) and (MgH2+Al+Ni+Y+Ce) exhibit relatively fast desorption kinetics and the lowest desorption temperature at about 240°C and 220°C, respectively. Finally, mechanical alloying of the non-stoichiometric compositions of (3MgH2+Fe) and (4MgH2+Fe) effectively generated a new ternary hydride, Mg2FeH6, with a very high yield of about 80wt% from the (3MgH2+Fe) mixture, which is a promising candidate for heat-storage. The research findings laid a clear and valuable foundation for future development of new and cost-effective Mgbased hydrogen storage materials with a high capacity, a low desorption temperature and rapid kinetics.