The work presented in this thesis is concerned with the accurate determination of material parameters and their use in three dimensional numerical simulation of the flow of rubber compounds through complex profile dies. In a first step, results from a study, based on classical rheometry conducted at the University of Wales Aberystwyth, are reviewed together with literature data. In conclusion of a comprehensive literature review, it is found that the existing literature on rubber compound material behaviour does not account for the separation of the different phenomena, i.e. in the most common case, wall slip effects are not separated from the shear behaviour and extensional viscosity is often neglected. The design of a novel in-line rheometer is presented, as classical laboratory rheo­metry is not considered adequate for taking into account the deformation history of the material as it proceeds through the extruder located upstream of the pro­file die. Extensive results gathered with this rheometer are used in an inverse material parameter determination scheme to obtain the parameters for the shear thinning, wall slip and extensional behaviour of the material. Subsequently, the new material parameters are used in the numerical study of a generic profile die especially designed for this purpose in order to display the various flow problems occurring in the real extrusion process. The design and instrumentation of trials on a profile production line at the in­dustrial collaborators site (Cooper Standard Products Ltd., Maesteg) for the aforementioned generic profile die are described. Experimental results for the flow distribution between the various limbs of the profile are compared with simulations. It is concluded, that the inclusion of extensional viscosity effects in the simulation is required, as a preliminary to the use of simulations in a computational optimisation scheme for profile dies.

A comprehensive study of the fatigue behaviour of a polyurethane acrylate resin and glass fibre reinforced composites has been undertaken. In the first part, three types of resins were tested: polyurethane vinyl ester, polyester and polyurethane acrylate, which was formulated to have superior properties. Three different types of glass fibre cloth were used for reinforcement, a woven roving and two novel stitch bonded Ulticloths. The [0/90]2s and [+/-45]2s lay-ups were prepared in order to investigate the effects of matrix, cloths and lay-up on fatigue strength and life time. Polyurethane acrylate composites proved to be superior to the polyester resin. The study on damage mechanisms also showed that the first damage was matrix cracking followed by interfacial failure, debonding, delamination and fibre facture which accumulate from the initial cycles until failure. The second part of this study concentrated only on polyurethane acrylate resin reinforced with Ulticloth [90/0]2s and Biaxial Ulticloth [+/-45]4 lay-ups. The data were produced to compare the effect of environment such as air, distilled water and seawater on the composite with tension-tension and tension-compression loading. With the [90/0]2s lay-up the fatigue strength and lifetime were reduced by the presence of distilled water and seawater. Once again, during fatigue testing with R=0.1, microscopic observations showed that these composites suffered severe damage. Samples tested in seawater had more damage compared with samples tested in air and distilled water. The last part of this research was to investigate the modulus degradation during the fatigue life. This investigation revealed that the modulus degradation on all laminates was dependent on stress ratio and lay-up. The modulus of [90/0]2s lay-ups was degraded during fatigue tests and this modulus degradation curve could be divided into three stages. The most clear damage occurring in [+/-45]4 was delamination which happened at both types of stress ratio, R=0.1 and R=-l. Analysis of some microscopic fractography has been carried out to support the observations.

In light of recent European legislation, an increase in recycling and recovery activities is required in the electrical and electronic sector in order to meet stipulated targets. For waste plastics this also includes the separation of plastics containing brominated flame retardants from those that do not. Studies into the FTIR (Fourier transform infrared) spectra of a collection of plastics from waste housings for computer equipment and comparisons with spectra from a selection of flame retardants, as well as testing different plastics identification systems have concluded that infrared spectroscopy cannot be used to detect flame retardants in plastics in the current state of technology. However flame retardants may be detected by using a combination of identification techniques such as IR (infrared) for plastic identification and pyrolytic spectroscopy for additive detection. The effects of recycling and blending on a commercial scale have been assessed on mechanical properties of the four most used plastics in computer equipment housings. Recycled ABS (acrylonitrile-butadiene-styrene), HIPS (high impact polystyrene), modified PPO (polyphenylene oxide) and PC (polycarbonate) /ABS alloy were tested in the pure form and as various blends of ABS and HIPS, HIPS and modified PPO (mPPO), ABS with PC/ABS and a blend of all four plastics. Properties tested were tensile and impact properties, DMT A (dynamic mechanical thermal analysis), viscosity, molecular weight and surface and bulk microscopy. Generally changes to mechanical properties following recycling of pure ABS, HIPS, PPO and PC/ABS are quite small, although there are slight reductions in ductility for HIPS and mPPO. All plastics used in this study appear unaffected by the presence of a small proportion of another plastic, although at higher blend proportions impact strengths of ABS/PC/ABS deteriorate, properties of ABS/HIPS blends remain unaffected and larger proportions of HIPS/PPO are beneficial to all properties. These results indicate that a plastics identification system probably does not need to be exactly 100% accurate.

This thesis describes the investigation into finding a safer alternative to the polychloroprene cross-linking agent ethylene thiourea (ETU). The novel approach of utilising spectroscopic analysis in combination with a study of mechanical and physical properties of polychloroprene was employed. Currently the most effective cross-linking system for polychloroprene is ETU in combination with zinc oxide (ZnO). However, due to the health risks associated with it, ETU may in the future be banned or heavily regulated, thus a replacement is sought. An investigation of the cross-linking mechanisms of ETU alone, and ETU in conjunction with ZnO was completed. This was necessary as polychloroprene cross-links differently to many other polymers. The study was carried out using model compounds, such as amines and thiols, in addition to work on more widely used accelerators, including thiurams and dithiocarbamates; this revealed that at least three disparate mechanisms are in operation. These mechanisms, comprise one of a cationic nature employed by ZnO, a bis-alkylation mechanism of ETU and a new proposed mechanism seen when ETU and ZnO work together synergistically. This new mechanism shows ZnO activating the polymer chain, followed by the sulfur of ETU creating a cross-link. Using this new mechanism, several new accelerators were proposed. These accelerators contain a dithiocarbamate group and are complexed with diamines. The diamine present acts as an activator and the dithiocarbamate group a cross-linker. These new accelerators were tested in pure polychloroprene rubber on their own, and in combination with tetrabenzyl thiuramdisulfide (TBzTD) or ZnO. All the proposed accelerators were able to cross-link. The replacement which most closely matched ETU, in terms of physical and mechanical properties of the vulcanisate was a complex of piperazine-1-carbodithioic acid and 1,3-diaminopropane (named PNA5). This accelerator was taken forward and tested in a filled commercial master batch. As a successful conclusion to the project a complete PNA5-based system was shown to closely match the performance of an ETU system in a master batch. Concomitantly the use of a multi-functional additive (a complex formed between stearic acid and 1,4-diaminobutane) allowed a reduction in ZnO needed, due to environmental concerns.

Molecular dynamics simulation method was used to investigate the effect of nanofillers on fracture strength and energy dissipation of polymers, including nanofillers contents, interaction strength between the nanofillers and polymer chains, relaxation time and geometry of the nanofillers. Molecular dynamics simulation results revealed that the addition of layered silicate can improve the fracture strength of polymers. The interactions between the surface of layered silicate and polymer chains, and the difference between the relaxation times of layered silicate and that f polymer chains have significant influences on the fracture strength and energy dissipation of polymers. For these polymers, which Tgs are lower than room temperature, such as polyurethane, or nearby (or equal to) room temperature, such as Nylons, the nanoplatelets can always enhance the mechanical properties. However, for these polymers, which Tgs are higher than room temperature, such as epoxy and polystyrene, the addition of the nanoplatelets does not work well for toughening these polymers. If one wants the nanoplatelets to be working for toughening these polymers, it is necessary to build up a stress relaxation interface between the polymer matrix and the nanoplatelets, such as the modification of the surfaces of nanofillers using coupling agents. When the relaxation time of the polymer is long enough, the incorporation of nanofillers into the polymer will cause the polymer to become more brittle. This result explains why the toughness of epoxy/ clay nanocomposites becomes poor. The simulation results clearly revealed that' the orientation of nanoplatelets is reversible at low strain of 50% suggesting that additional energy dissipation only results from the frictional sliding at the interface, whereas the orientatiqn of nanoplatelets at large strain of 200% showed more irreversibility suggesting that the additional energy loss results from both the interfacial frictional sliding and the orientation of the nanoplatelets. The additional dissipated energy was also influenced by the strength of interactions between polymer chains and clay platelets. The stronger interactions the more energy dissipated. Molecular dynamics simulation results revealed that the geometry of nanofillers also affect the mechanical properties of polymer nanocomposites. The enhancement if carbon nanotubes on the mechanical properties of the polymers are enhanced the greatest by carbon nanotubes.

No description available.

Proton beam writing is a direct write lithographic technique that uses finely focused MeV proton beams to create structures in a target material. The depth the protons travel in a material is dependent on its energy, this unique property of proton beams allow multi level structures to be created in materials. PBW has been demonstrated successfully on semiconductor materials, glass and polymers. This thesis is a study of the application of PBW in creating Micro Electro-Mechanical Systems (MEMS) in a polymer SU 8 and SU 8 polymer nano composite with silver, and shows experimental steps, theory and computer simulations involved in creating an electrostatic actuated micro-gripping device. Proton beam writing in silver SU 8 composite results in the creation of electrically conducting microstructures. The unique predictability of the range of protons in materials is leveraged in the creating of free standing conducting cantilevers structures which are used as the building blocks for a micro gripping device. The electrostatic actuation has been modelled using a finite element modelling software Sugar 3.1, and the results are comparable with actual actuations in a realized micro-gripping device.

This thesis describes published work undertaken over the last 17 years. The main focus is the development and utilization of the microscale combustion calorimeter (MCC) and how it helps us understand the flammability of materials. A reproducible way to quantitatively assess material flammability was needed. The simplest approach is based on the molecular structure of a material to determine which moieties influence the flammability. This approach is based on material properties that can be measured using small-scale thermal analysis methods such as Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and the MCC. Properties such as thermal stability, heat of gasification, and heat of combustion provide key information about materials' flammability. Tests such as LOI, UL-94 and other Bunsen burner type tests provide pass/fail type results. These types of tests are not quantitative and are dependent on physical properties and extrinsic parameters such as sample geometry and orientation. They do not provide a true measure of flammability, and formulations can be optimized to pass the test even though they are highly flammable. A more quantitative approach is to use larger bench scale flammability tests such as cone calorimeter and Ohio State University (OSU) fire calorimeter. Although these tests are also dependent on the physical properties and test geometry, they measure properties such as burning rates, mass loss rates, and combustion efficiency under different imposed fire scenarios from which material properties can be derived. The ultimate flammability test for a material is to subject it to a fire in a real-life scenario where other materials are present, a full-scale fire test. These tests can involve a single item or combinations of items. These tests are highly dependent on physical and material properties and are useful for making direct comparisons of one scenario to the next, for properties like flame spread and time to flashover. Measurements have been made using all of the thermal analysis and fire test methodologies listed above. Correlations between the test methods have been drawn and the theory relating them derived. Predictive methods for estimating polymer flammability from molecular structure have been formulated using a molar group contribution approach. Methods for predicting fire performance in the bench scale tests from the small scale test measurements have also been derived. Modelling the bench scale fire performance in the quantitative tests as well as determining a probability for the rating in the pass/fail type bench scale tests for a range of polymeric materials has been undertaken. This type of work in the small- and bench-scale has helped identify materials that perform well when subjected to the harshest fire conditions in the full-scale. The ultimate goal being to save lives by preventing deaths due to fire through the development of more fire-safe materials.

Physical aging is the general term used to describe changes in the properties of glassy materials as a function of storage time, at a temperature below the glass transition, Tg. Extensive studies have been carried out on homopolymers and copolymers but fewer investigations have dealt with aging in polymer blends. This Thesis reports a detailed study of physical aging in polymer-polymer mixtures where strong intermolecular interactions are active between components. Miscible blends incorporating poly(4-hydroxystyrene) (P4HS) or styrene-co-4- hydroxystyrene (SHS) and poly(ethyl methacrylate) , poly(ethylene oxide) , poly(4- vinylpyridine) and poly(methyl methacrylate) were prepared. Fourier transform infrared spectroscopy was used to extract qualitative and quantitative information on the strength and number of hydrogen bonds. The effect of temperature and dilution of the hydrogen bonding sites is discussed and a comparison made between different systems. Enthalpic relaxation data for a series of homopolymers and copolymers, including poly(methyl methacrylate-co-ethyl methacrylate), and blends incorporating P4HS and SHS were collected and analysed using Cowie-Ferguson relaxation model. It is found that the enthalpic relaxation for all P4HS and SHS blends increases upon increasing hydrogen bonding strength between the components. The relaxation rate also increases with increasing strength of interaction as well as chain rigidity. Average activation energies were calculated of all homopolymers, copolymers and blends under study. This parameter is shown to be correlated to polymer structure and polymer-polymer interactions and it is therefore useful to compare the aging behaviour of different systems.

Emulsion copolymerisation of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) at 70 °C afforded sterically-stabilised latexes at approximately 10% solids. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) studies confirmed that relatively narrow size distributions were obtained. Lightly cross-linked latexes acquired cationic microgel character upon lowering the solution pH, as expected. Poly(2-(tert-butylamino)ethyl methacrylate) (PTBAEMA) latex proved to be an effective Pickering emulsifier at pH 10, forming stable oil-in-water emulsions when homogenised with either n-dodecane or sunflower oil. These Pickering emulsions exhibited pH-responsive behavior: lowering the solution pH to 3 resulted in immediate demulsification due to spontaneous desorption of the cationic microgels from the oil/water interface. The secondary amine groups present on TBAEMA residues can react with isocyanates forming a urea linkage. Thus PTBAEMA latex-stabilised Pickering emulsions were readily converted into covalently cross-linked colloidosomes following reaction with a polymeric diisocyanate (which was dissolved in the oil phase prior to homogenisation). Such colloidosomes survived both an acid and ethanol challenge, confirming their robust latex super-structure. Copolymerisation of TBAEMA with styrene (S) afforded copolymer latexes with higher glass transition temperatures, which facilitated imaging of colloidosomes via SEM. However, the shell of these colloidosomes was found to be highly permeable, with the rapid release of a small molecule dye being observed by UV visible adsorption spectroscopy. Lightly cross-linked poly(2-(diethylamino)ethyl methacrylate) (PDEA) latex particles of 190 to 240 nm were prepared via emulsion copolymerisation at 10% solids in the presence of a hydrophilic poly(ethylene glycol)-based macromonomer. A latex-to-microgel transition occurred on lowering the solution pH below the latex pKa of 6.9. When using dilute HCl/KOH to adjust the aqueous pH, a systematic reduction in the cationic microgel hydrodynamic diameter of 80 nm was observed over ten pH cycles. No such size reduction was observed when using CO2/N2 gases to regulate the aqueous pH. PDEA microgels do not stabilise Pickering emulsions when homogenised at pH 3 with n-dodecane, sunflower oil, isononyl isononanoate or isopropyl myristate. In contrast, PDEA latexes proved to be a ubiquitous Pickering emulsifier at pH 10, forming stable oil-in-water emulsions with each of these four model oils. Lowering the solution pH from 10 to 3 resulted in demulsification within seconds due to spontaneous desorption of the swollen cationic microgels. Six successive demulsification/emulsification cycles were performed on these Pickering emulsions using HCl/KOH to adjust the solution pH. Demulsification could also be achieved by purging with CO2 gas to lower the aqueous pH to pH 4.8. However, this required prolonged purging for 2 h. Finally, the kinetics of swelling of near-monodisperse, lightly cross-linked 200 nm PTBAEMA, PDEA, poly(2-vinylpyridine) (P2VP) and poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) latexes was investigated by the pH-jump method using a commercial stopped-flow instrument. The kinetics of swelling of each latex-to-microgel transition for sub-stoichiometric acid/amine molar ratios (at the particle pKa), stoichiometric and excess acid was examined. Fastest swelling times (tens of milliseconds) were observed for P2VP particles, followed by PTBAEMA and PDEA, (for which swelling times were comparable), with PDPA latexes swelling the slowest. This rank order correlates with the monomer repeat unit mass, which suggests that the cationic charge density plays an important role in determining the swelling kinetics Kinetics of deswelling for P2VP and PTBAEMA were also examined. Slower deswelling time scales (tens of seconds) were observed which we attribute to the formation of a latex-type skin upon deprotonation.