As an aid to understanding the mechanics of mixing in an internal mixer laboratory scale trials have been carried out using a mixer having a transparent plastics chamber. The use of a transparent rubber and coloured 'markers' then permitted direct viewing of the characteristic flow patterns deriving from the use of three fill factors. These mixing trials have indicated the rheological properties which must be measured in order to predict the mixing behaviour of a rubber. Also considerable information is contained in the visualisations which will aid further work into control and instrumentation strategies and into fundamental design/mathematical modelling studies. A laboratory Banbury mixer and Brabender Plastograph are used to prepare the rubber compounds which are then characterised for the dispersion of compounding ingredients. For carbon black dispersion studies several techniques are employed. Capillary rheometry is used to study their stress-strain rate relationships and to obtain die swell, shear and tensile properties. Creep and elongational tests are also carried out on uncured mixes. In addition measurements on Mooney viscometer, Monsanto rheometer and analysis of bound rubber are made. These tests for filler dispersion are supported by microscopic examination of microtomed sections. Work is also geared to examine properties that are not only sensitive to changes in levels of carbon black dispersion but also that which are readily measured and can be used in industry. Measurements of mechanical phase angle and electrical resistivity are considered. Dispersion of non-black compounding ingredients is studied by X-ray microradiographic technique and the analysis of vulcanisate properties. To relate the performance of the Plastograph and Banbury mix the concept of mixing energy per unit volume of material is used.

Screw extrusion is widely used in industry today, but little is known about the design and operation of this type of equipment outside of the polymer industry. With the advent of high performance, high value ceramic materials, it has become important to understand how to produce product consistently and economically. A mathematical model has been devised for a flooded screw that brings together paste rheology and a model of screw extrusion developed from methods with frictional solids flow. The resulting model defines the paste using parameters derived from experiments with an instrumented ram extruder. The governing equations are applicable to the flow in a single screw extruder channel of any cross-section. Experiments have been performed both with and without flow on a 20mm diameter laboratory extruder using a set of screws of varying angle and depth together with pastes of various rheologies. Pressure measurements from experiments without flow could show a marked offset from predictions with screws of low helix angles, although the effects of changing the screw speed universally yielded good agreement. It is hypothesised that this pressure offset was due to a localised enhancement of the static shear stress value at the rapidly moving barrel surface. This enhancement was possibly caused by either pressure or localised changes in the rheology in this high shear region. If the static shear stress parameter is adjusted in the model then the predictions show universally good agreement with these experiments. Experiments with flow also showed general consistency with predictions made by the model, as did experiments carried out on a 3" diameter industrial machine The interpretation of the performance of a fully flooded screw with flow was complicated by the interaction of the screw and the die Future work should centre upon the effects at the barrel surface and the improvements of both pressure and rheology measurement. An attempt should also be made to extend the model to describe flow situations of greater complexity, taking account of converging channels and leakage around the flights. The flow of pastes in twin screw extruders should also be addressed.

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Many materials require functionally graded cellular microstructures whose porosity (i.e. ratio of the void volume to the total volume of a material) is engineered to meet specific requirements and for an optimal performance in diverse applications. Numerous applications have demonstrated the potential of porous materials in areas ranging from biomaterial science through to structural engineering. Polymeric foams are an example of a cellular material whose microstructure can be considered as a blend of material and nonmaterial zones. While a huge variety of foams can be manufactured with homogenous porosity, for heterogeneous foams there are no generic processes for controlling the distribution of porosity throughout the resulting matrix. Motivated by the desire to create a flexible process for engineering heterogeneous foams, this work has investigated how ultrasound, applied during some of the foaming stages of a polyurethane melt, affects both the cellular structure and distribution of the pore size. After reviewing the literature concerning foam chemistry, ultrasound and sonochemistry, series of experiments were performed that used an ultrasonic field created by a sonotrode irradiating in a water bath containing a strategically placed vessel filled with foaming reactants. Prior to this, the acoustic field in the bath had been accurately mapped so that the acoustic pressure conditions within the foam container were known. During the foam polymerisation reaction, the acoustic pressure in the water bath varied causing the bubbles to pulsate in a state of ‘stable cavitation’ (i.e. rectified diffusion). This pulsation of the bubbles pumped gas from the liquid to the gas phase inducing them to increase in volume. The eventual solidification resulted in a porous material with a cellular structure that reflected the acoustic field imposed upon it. The experimental results revealed how the parameters of ultrasound exposure (i.e. frequency and acoustic pressure) influenced the volume and distribution of pores within the final polyurethane matrix: it was found that porosity varies in direct proportion to both the acoustic pressure and the frequency of the ultrasound signal. The effects of ultrasound on porosity demonstrated by this work offer the prospect of a manufacturing process that can control and adjust the cellular geometry of foam and hence ensure that the resulting characteristics of the heterogeneous material match the functional requirements.

The objective ofthis research was to investigate how gas plasma treatments can alter the surface morphology of polypropylene (PP) fibres and tape with the main focus of the work on the tape. The morphological changes caused by exposure to controlled argon, nitrogen and oxygen gas plasmas were characterised using both Scanning Probe Microscopy (SPM) and Scanning Electron Microscopy (SEM). The research has demonstrated that the extent of surface deformation was dependent on the treatment gas used and on the process parameters. Surface deformation gradually increases with increasing process time and power. Oxygen plasma was found to be the most aggressive plasma followed by nitrogen, with argon the weakest. Different process parameters used during extrusion have an important effect on the nature of the PP morphology. This thesis also demonstrates how the surface morphology can be altered by different cooling techniques and by drawing the tape once extruded. SPM analysis shows a transformation in the spherulitic morphology from hill to valley shaped spherulites when gravity spun PP tape was cooled in water as opposed to air. Deformation of the spherulitic structure to a fibril struct~re was also observed, which became more apparent from gravity via as-spun to fully drawn tapes.

Polymer laminated steel is increasingly popular in the packaging industry as a competitor to lacquered steel and as a product in its own right. It does however have many benefits over lacquering such as the ability to coat before processing and absence of harmful emissions. One key requirement for such materials is good adhesion between polymer and steel. This work examines the bonding of polymer film to steel substrates in material where the adhesion is relatively good. A test method was developed which produces quantitative results for the strength of this adhesion. It was shown that this method was reproducible and differentiated between good and excellent adhesion. From the results obtained using this test method the effect of substrate and film variations were investigated using a combination of tin and chrome coated steel and polyethylene terephthalate (PET) and polypropylene (PP) polymer films. For the tin substrate it was found that the surface finish affected the adhesion of PET but there was less if any effect on PP adhesion. This was thought to be down to the failure mechanism that occurred in the PET being interfacial whereas for the PP the failure occurred within the polymer and so was not affected so much by surface characteristics. This was confirmed using surface analysis techniques. Chrome coated steel samples were also tested but results from these were less conclusive.

No description available.

No description available.

No description available.

No description available.