This thesis describes a programme of work whose aim was to develop and characterise a novel organoclay derived from montmorillonite clay and the amphoteric surfactant cocamidopropylbetaine (CAB), a plant oil derivative, and to test its compatibility with poly(lactic acid) (PLA). Clay minerals such as montmorillonite increase the mechanical and physical properties of polymers when well dispersed within the polymer matrix, a condition that is more easily achieved when the clay layers are coated with a surfactant such as a quaternary alkyl ammonium compound (QAC). In the first part of the thesis the structure, purity and thermal behaviour of the CAB were characterised and the solubility parameter of the molecule was calculated and compared with that of a surfactant used in a commercial organoclay. The effects of concentration and pH on the uptake of the surfactant by montmorillonite were characterised by analytical and spectroscopic methods including X-ray diffraction analysis. The effect of surfactant loading on the thermal stability of the organoclay was studied using thermogravimetric analysis (TGA). The possibility of a reaction between CAB and PLA was also investigated by thermal and spectral methods. In the second part of the thesis, composites of the novel organoclay and PLA were manufactured by solution casting from chloroform, and melt compounding using a torque rheometer. It was found that intercalated/exfoliated nanocomposites could be made by either method. The biodegradability of the nanocomposites in composting conditions was also investigated. The study showed that CAB can be used to manufacture organoclays that confer useful improvements in the properties of PLA in terms of thermal stability and mechanical strength and on this basis merits further study. It also showed that organoclays based on CAB are a useful addition to the range of tallow-derived organoclays currently available.

Fuel cells are widely researched and have applications in residential, automotive, marine craft and space. Their efficiencies are typically 60 % as a result of their electrochemical conversion and due to this they are considered beneficial to the reduction of CO2 which accounts for 77 % of all greenhouse gasses. Polymer electrolyte membrane fuel cells are the most suited to automotive applications for their low operating temperatures, high power densities and fast start up times. Currently there are many problems still to be rectified before commercialisation takes place, one of which is the performance and manufacture of bipolar plates. The elimination of corrosion, reduction of mass and the improvement of mechanical, electrical and thermal conductivity properties are the main aims to progress bipolar plate technology. In addition, the large numbers of bipolar plates required in automotive fuel cell stacks is in the order of 400 plates and so mass production will be necessary to meet future demands as well as reduce costs through cheap production processes. In order to meet these requirements polymeric based bipolar plates with conductive fillers have been pursued. The use of highly conductive, low density, low cost and corrosion resistant materials that can be utilised in production processes such as injection and compression moulding are ideal candidates for bipolar plates. However, balance of electrical/thermal conductivity and mechanical strength becomes the major task as highly conductive composites result in low mechanical strength. Therefore three conductive powders, a carbon black, graphite and magnetite (iron II,III oxide) were used as fillers in a polyethylene matrix to study the balance just mentioned for the two manufacturing processes stated above. The composites were tested for their electrical and thermal conductivities and mechanical properties and compared to the US Department of Energy targets for 2015. The carbon black composites exhibited better electrical conductivity than the other fillers where at 65 wt% the conductivity was ~24 S/cm for through plane conductivity and had a flexural strength of ~32 MPa. Injection moulding produced composites with more material stability and greater mechanical strength than compression mouldings although compression mouldings produced composites with higher thermal conductivities where graphite displayed the highest thermal conductivity of ~2 W/mK. Modeling of the experimental results using Mamunya models for electrical and thermal conductivities and a modified Kerner s equation for mechanical moduli were conducted. Models showed reasonable agreement with the experimental data where parameter tuning and deviations from the model were used to describe microstructural behaviour with regards to electrical tunnelling effects, link, node and blob structures and stress transfer at the filler-matrix interface.

Polyimides have become important materials in the manufacture of a large number of technical products, e.g. varnishes, coatings etc, as they can fulfill a number of requirements. One such requirement is that they have to withstand high temperatures without deterioration of their properties. The work is based on the expectation that the temperature resistance and thermal stability of polyimides can be enhanced by introducing inorganic heat resistant materials, such as silicates, to form hybrid mixtures known as "ceramers". The systems considered in this work are based on linear aromatic polyimides and silica networks produced by the sol-gel route. Solutions of polyamic acid and partially polymerised tetraethoxysilane (TEaS) solutions are converted into ceramer films by solvent evaporation, followed by imidisation and condensation reactions through stepped temperature rises up to a maximum of 350°C. Phase separation is prevented by the use of small amounts of compatibilising agent glycidyloxypropyltrimethoxysilane (GOTMS) or by addition of triethylamine or tributylamine catalysts. By controlling the rate of condensation reactions in the two components different morphologies are obtained, varying from semi-interpenetrating networks of linear poyimides within highly crosslinked silica chains to finely dispersed heterogeneous systems exhibiting etiher a co-continuous or particulate microstructure. As each phase consists of interpenetrating networks of the two components at different concentrations, it is inferred that phase separation takes place through a spinodal decomposition. The crosslinking density of the silica network was reduced by diluting the tetraethoxysilane component with minor quantities of· dimethyldiethoxysilane (DMES). The properties of polyimide ceramers were found to be intermediate between those exhibited by the individual components, depending on the details of the morphological structure. The most interesting characteristics of these systems are: (a) high modulus, high glass transition temperature and dimensional stability at temperatures greater than 250·C, (b) suppression of anisotropy in polyimide films by addition of silica, and (c) negative coefficients of thermal expansion below 100·C. The causes of this anomalous behaviour are not clear at this stage but it appears to be related to large volumetric changes taking place within the silica network as a consequence of the absorption and desorption of small amounts of water.

British Gas have been using polyethylene pipe and fittings for gas distribution since 1969. The medium density, and more recently high density polyethylene pipes are produced by a simple and well established extrusion process. Unfortunately the production of fittings, especially large diameter fittings is not so simple. Traditionally pipe fittings are made from either injection moulding or by other fabrication techniques which require subsequent cutting and welding of different parts to produce the finished article. Recently however the methodology has been developed to facilitate the production of fittings by rotational moulding. Incorporated into the new methodology is the ability to produce crosslinked fittings by peroxide inclusion. Crosslinking of the pipe fittings has a major advantage in that it produces a substantial improvement in the mechanical properties of the polymer. Of particular importance is the improvement in stress crack resistance. Stress cracking is presently the primary mode of failure in polyethylene pipelines. Cross linking should help to reduce the susceptibility of the pipeline to failure by this method. The purpose of this project has been to investigate the crosslinking process in two rotational moulding grades of polyethylene. In particular a study has been made of the relationships between various chemical and physical properties, and of how these change upon material modification. A series of compression moulded samples containing increasing levels of peroxide have been produced for both polymers. Characterisation of these samples was undertaken using such techniques as Differential Thermal Analysis, Fourier Transform Infrared Spectroscopy, Gel Permeation Chromatography, Gel Content and Microscopy. The results have shown that as peroxide concentration is increased gel content rises sharply before reaching a maximum value. In contrast to the gel content, the crystallinity of the samples was shown to decrease. Infrared analysis provided the facility to monitor the variation in molecule end group concentration with changing peroxide levels. It was found that increasing the level of peroxide resulted in a decrease in the concentration of terminal vinyl unsaturation in an inverse relationship to gel content results. Subsequent gel permeation chromatography analysis demonstrated that the terminal vinyl groups were being lost in a chain extension mechanism which resulted in an increase in the molecular weight of the samples.

Magnesium hydroxide is of growing interest as a halogen-free flame retardant, and has a high thermal stability, so it can be melt processed into most thermoplastics without premature decomposition. The hydrated mineral filler commences endothermic decomposition at approximately 340°C, withdrawing heat from the polymer substrate, releasing water of crystallisation to dilute the fuel supply. However, to be an effective flame retardant filler, high loadings up to 66% are required. This may cause detrimental effects on both rheological and mechanical properties of composites produced. Two synthetic seawater magnesium hydroxide fillers (DP393 and DP390s), of different morphologies but similar surface area, were selected as flame retardant fillers for polypropylene. These were coated with stearate, oleate, rosin and vinyl silane and compounded at 60% by weight into an injection moulding grade ofpolypropylene. The effect of filler morphology, coating agent, coating type and coating level on the crystallisation, rheological and mechanical properties of polypropylene were studied. DP393 is a one-micron platey structure which was found (by XRD) to be orientated parallel to the flow direction, whereas DP390s is a five-micron porous sphere residing isotropically within the matrix. Incorporation of uncoated magnesium hydroxide increased the overall crystallisation rate of polypropylene, causing orientation of the polymer b axis parallel to the flow direction, this being induced by the 001 crystal face of magnesium hydroxide.

This study centres on conductive polymers with particular reference to those exhibiting positive temperature coefficient of resistance (PTC) behaviour. Applications of PTC polymers are identified including, with special relevance to this study, automotive applications. The electrical properties and the structure of a particular conductive polymer that has a carbon black conductive filler and exhibits a positive temperature coefficient characteristic, have been measured. Early problems affecting the testing and service performance of these devices are described. Initial concepts of the factors affecting their structure and performance are outlined. The importance of the characteristic known as resistance linearity is described and its important relationship with device performance is noted. The results of a literature survey are detailed. Typical materials and manufacturing processes employed for the type of heater circuit central to this study are described. The results of initial testing and analysis of PTC heater circuits in relation to manufacturing process variables, ageing tests and service failure are summarised. The results of further testing of heater samples and analysis using advanced techniques including Fourier transform IR spectroscopy (FTIR), Calorimetric analysis with scanning microscopy (CASM), Auger electron spectroscopy (AES), Static secondary ion mass spectrometry (SSIMS) and Laser microprobe mass spectrometry (LIMA) are given. The structure of the PTC polymer used in construction of the heater circuit is examined with a high resolution scanning electron microscope (FEGSEM) and the distribution of the carbon filler is determined. Structural changes and changes in the distribution of the carbon resulting from thermal conditioning and other stresses are investigated. A cause of functional failure of heater circuits in service has been identified. Conclusions have been drawn and further work proposed.

No description available.

The aim of this thesis is to present the results obtained, to interpret them in terms of adsorbed rubber, interparticular rubber and matrix rubber, and to assess their relative importance in controlling the processibility and physical properties of silicone rubber. The secondary aim is to consider their relevance to the broader issue of the particulate reinforcement of rubbers.

The flow behaviour of post-consumer recycled polyolefins, their blends and layered-silicate nanocomposites was studied by capillary rheometry and freesurface melt state elongational measurements to assess suitability for foaming applications. A novel, extrusion foaming technique and a flow simulation model were developed to attempt to correlate flow and foaming behaviour. The recycled polyolefins were high-density polyethylene (HOPE), low-density polyethylene (LOPE) and polypropylene (PP) of high-molecular weight, suitable for extrusion; that also contained also paper and inorganic fillers. LOPE-PP and HOPE-PP blends were prepared in a batch mixer with and without compatibilising agents, ethylene-propylene rubber (EPR) and ethylene-propylene (EP) copolymer. Several mixing conditions (temperature, time, rotor speed) were used to modify the morphology and the flow behaviour of the blend systems. In shear flow diverse pseudoplastic index, zero shear rate viscosity and the extensional viscosities, whilst, in uniaxial extensional flow the effects of process conditions on strain energy density, elongation at break and melt modulus were detected. The melt strength of uncompatibilised LOPE-rich systems is generally higher. The use of small quantities of EPR, 2.5 and 5.0% (w/w) can further improve the rheological properties in uniaxial extension, but shear flow behaviour is virtually unchanged by the compatibilisers. EP didn't improve the extensional flow behaviour of HOPE-PP blends. The influence of processing conditions and composition on the preparation of melt intercalated HOPE and HOPE-PP layered-silicate nanocomposites was conducted as a way of enhancing foaming behaviour; montmorillonite particles were dispersed with the aid of a compatibilising agent. Ideal mixing conditions (temperature, rotor speed and time) were determined for these nanocomposites based on rheological measurements. In HOPE nanocomposites, the melt elongation at break is reduced and the tensile modulus increased. The clay content has a significant influence on the melt tensile modulus. Wall slip behaviour appeared enhanced comparatively to unmodified HOPE. In HOPE-PP nanocomposite blends it is possible to modify the melt tensile modulus and elongation by changing blend composition and clay dispersion morphologies. A finite element model of capillary die flow was developed using commercial simulation software to assist the interpretation of an extrusion foaming technique. Experiments were carried out using azodicarbonamide as a blowing agent and a capillary rheometer and extruding the materials through a capillary die. Extruding at a shear rate of 300s-1 and at a temperature close to the melting point yielded the lowest foam densities; LOPE, the material with the highest melt strength and extensibility, achieved a density of 430 kg m-3. Blends of HOPE-PP, LOPE-PP and HOPE-PP nanocomposites didn't show an improved foaming behaviour with densities always above 600 kg m- 3 Oensities of 360kg m-3 and 500 kg m-3 were obtained with HOPE nanocomposites and unmodified HOPE, respectively.

Several additive manufacturing processes have been developed for plastic parts. However, there is an ongoing interest to increase the functionality of these parts which are mainly considered as prototypes due to the material and process limitations. This research investigated a novel additive approach for producing a functional engineering plastic, nylon 6. The idea was to combine inkjet printing technology and anionic polymerisation of caprolactam by depositing mixtures of caprolactam with activator and catalyst on top of each other under the appropriate conditions. An experimental setup was integrated based on two identical jetting assemblies with pneumatic and thermal control, synchronised with a deposition system for the reaction of the mixtures upon radiation heating. Different offline material characterisation and inline process monitoring methods were employed to obtain an understanding of the material behaviour at each stage of the research. These included the use of high speed imaging, fluorescent microscopy, particle tracking and image analysis tools. Samples were monitored before and after the drop-on-drop deposition and radiation heating, and then assessed by thermal analysis to find the appropriate conditions for the reaction. It was found that although some monomer conversion was achieved, the rates were much less than with the bulk polymerisation approach. Jetting of thousands of tiny droplets in air could have resulted in a very high monomer deactivation. This highlighted the importance of the environment as a more significant parameter for jetting of nylon 6 compared with the conventional method.