The present work has successfully used an ingenious experimental technique to make a detailed examination of flow fields and fibre orientation patterns in a number of geometries. The experimental technique consisted of dispersing short glass fibres in mixtures of epoxy resins with matching refractive indices to that of the glass fibre. This made the glass fibres to 'disappear' in the mixtures and resulted in transparent mixtures. Light-reflective nickel particles and opaque tracer fibres were added to the mixture in order to investigate velocity fields and fibre orientation patterns. Experiments have covered concentrated, semi-concentrated, and (almost) dilute regimes. It has demonstrated a number of phenomena in flow-induced fibre orientation particularly in the concentrated region which have not been described before, and which should be taken into account in any predictive theories of fibre suspension flow and orientation. In the highly-concentrated suspensions, where C > (d/21), plug-flow type velocity fields exist. (Here C is the mixture concentration, d is the fibre diameter, and 21 is the fibre length). The fibre resin mixtures behave as non-homogeneous continua where fibre clumps are separated by resin-rich areas. These clumps apparently deform under shear, but seem capable of elastic recovery, facilitated by shear-induced clump rotation. In the semi-concentrated regime, where (d/21)<SUP>2 < </SUP> C < (d/21), expected degrees of alignment are diminished by fibre-fibre interactions. In this concentration regime and in some flow situations there is some evidence of rate dependence of alignments achieved, i.e. dependence on viscous stress levels. In the (almost) dilute regime, where C is just higher than (d/21)<SUP>2</SUP>, the fibre behaviour is in theory predictable from single fibre mechanics if the flow fields are of the linear type. However, in practice this is seldom the case. For this reason a theory has been developed and implemented in a computer program, which predicts fibre motion in arbitrary velocity fields.

The process of extrusion and calendering involves complex deformations over a broad range of temperatures, which induce various residual stresses and preferred orientations. The primary aim of this project was to study the consequence of calendering conditions, composition and place-to-place variability on aging effects, levels of residual stresses and orientations. Standardised procedures have been developed in this study to monitor the recovery of plastic sheet produced in this way, and to characterise the residual stresses and orientations induced by the processing. In the main technique that was developed, samples were taken at regular intervals across sheets of two copolymer grades and subjected to a series of heat treatments at successively higher temperatures. Other techniques that were used included monitoring dimensional changes following the machining of thin samples from the calendered sheet. The copolymer series consisted mainly of poly (methyl methacrylate) (PMMA) with the addition of 3 or 10% ethyl acrylate (EA). Strong evidence has been found for the existence of three distinct regimes in the recovery of these PMMA/ EA copolymers. It has been argued that recovery prior to the onset of the glass transition is due to aging effects induced particularly by cooler calendering rolls. Control samples have shown that residual thermal and viscoelastic stresses relax between the onset of the glass transition and Tg, whereas orientation relaxes above Tg. The length and curvature changes of samples from the four acrylic sheets were interpreted in terms of these three recovery mechanisms. It was found that residual stresses are highest in the copolymers calendered under conditions of low roll temperatures and high line speeds. The opposite processing conditions, i.e. high roll temperatures and low line speeds lead to increased chain extensions. When the two copolymers were processed with the same roll temperatures and line speed settings, greater chain extensions were induced in the 3% EA copolymer, although the residual thermal stresses were similar. The extension of the chain constitutes one form of orientation which is not directly related to the alignment of segments between entanglements, which was relatively unaffected by calendering conditions or the addition of EA.

In the first part of this research work a new version of the cooling simulation software was constructed by changing the old convection module, which used the commercial software package POLYFLOW, to a new version using an alternative code developed in the Centre for Polymer Processing at the University of Wales Swansea, called Fantazt. This change introduced a large number of modifications in order for the new convection module to work in harmony with the rest of the program. Also many improvements have taken place in the new version, with respect to the computational time and the functionality of the software. The new version had to be tested on a large variety of profiles and be able to reproduce results identical with the computed results that have been previously provided by Kömmerling using the POLYFLOW version. In addition, a detail investigation regarding the convergence of the cooling simulation software was carried out. In the second part of this research work, a critical overview of the mechanical model has been presented. The main scope of this section was to carry out a detailed investigation of all the aspects of the mechanical model. Throughout this research, aspects as the convergence behaviour of the software were thoroughly examined. The outcome of this detailed investigation was the development of a new version of the mechanical model. The present work has provided detailed insights and understanding of the performance of the mechanical software, and produced improved versions of the code. The work has identified a number of further developments that are required. Throughout the research period, strong and valuable synergies have been developed with previous and parallel research works between Swansea University and Kömmerling Kunststoffe, aiming to provide a better understanding of the parameters that affect the calibration process and the use of the simulation software.

High Density Polyethylene (HDPE) and HDPE filled with Carbon Black (CB) and/or Electro Graphite (EG) are utilized in commercial applications, whereby the materials come into contact with highly alkaline solutions and so the effects of such environments are critical. This study investigates the potential environmental stress cracking (ESC) effect of pH 13.5 Sodium Hydroxide (NaOH) solution on these polyethylene based materials. A range of temperatures from 23°C to 80°C was used. Various mechanical testing methods were employed, including constant strain three point bend, tensile creep, constant strain rate tensile tests and three point bend creep tests. The three point bend techniques revealed the clearest differences between the tests performed in NaOH and air. Samples were subsequently investigated using optimal microscopy, scanning electron microscopy (SEM) and IR spectroscopy techniques. PE was found to undergo ESC in the presence of NaOH at combinations of high strains (≥14%) and high temperatures (≥60°C). The addition of carbon filler reduced the ductility of the material and increased its strength. ESC effects were observed at lower strains for the filled materials and this was related to the amount of added filler. Addition of filler was found to embrittle the material, whereby CB had a more significant effect than the equivalent amount of EG. The CB particles were finer, resulting in the polymer chains being less easily deformed. The EG particles were much larger than the CB ones and due to the nature of graphite, a lubrication effect on a microscopy level, resulted in the samples reaching greater strains than the CB filled ones. The FTIR study did not reveal any chemical changes in the damaged samples; however, the technique used was limited in its effectiveness. When samples tested in both air and NaOH became damaged under the same test conditions, the material properties defined the type of damage occurring. The SEM study did clearly show an embrittling effect resulting from the NaOH, when damage occurred in NaOH but not in air; the fracture surfaces were seen to be smoother for the NaOH tests, when compared to the control tests. The proposed action of the NaOH is to cause embrittlement of the polymer by causing surface energy reductions and hydrolysis, leading to the breakdown of the polymer backbone.

Recycled Polyvinyl Chloride derived from post-consumer bottle products has been investigated to find the effects of contamination upon mechanical and re-processing properties. Aspects of recycling technology, structure-property relationships of PVC and the materials reaction to thermal degradation are also reviewed in dissertation form. Tensile, fatigue and environmental stress cracking properties of two recycled PVC materials (of a pulverised and flake raw form), from different stages of the recycling process, were tested in relation to those of two group PVC bottle materials. Generally, mechanical results displayed an inferiority of the recycled materials compared to the performance of the purer grades, although the pulverised recycled grade (RP) did not show a large drop. Scanning electron microscopy (SEM) of fracture surfaces from tensile and fatigue specimens, revealed that recyclate materials were pervaded with impure particles that served to interfere with stress transfer mechanics and altered their yielding characteristics. Molecular weight analysis (Gel Permeation Chromatography, GPC), of the all four materials tested, showed the molecular weight of the recycled materials was not significantly affected by the recycling process used. Separation of impurities by selective dissolution of the PVC matrix showed a contamination of 0.31%wt insolubles. Infrared analyses of solution cast films and insolubles were then performed, revealing a definite presence of polyethylene Terephthalate (PET) with polystyrene and polyethylene present in minor proportions. Batches of the two recyclates and a bottle flake (BF) material were subjected to simulated multiple recycling using a torque rheometer. Molecular weight and Infrared analyses were performed to assess the amount of degradation occurring during re-processing. Results from both analysis techniques were in agreement with a rapid degradation of the two recycled grades when compared with the BF material. Further multiple recycling was then performed on BF mixed with a small proportion of polyethylene which showed that this contamination accelerated degradation processes. Re-processing of BF material with additions of new material at each recycled pass indicated the existence of a threshold proportion of new material that provided a surrogate stability to the melt.

The present work is concerned with the investigation of the slit die extrusion of molten polymers, and a systematic strategy is developed for the modelling of its major aspects. The objective is to provide a fundamental understanding of the flow phenomena within such a die, coupled with thermal and mechanical interaction of melt and die body, and to provide user friendly software for analysis and design. Isothermal, non-Newtonian flow in the large aspect ratio channels of such dies is modelled using a Hele-Shaw formulation. The pressure field in the die causes a change of the flow channel dimensions, and hence alters the melt distribution. An experimental technique is applied to determine this die body deflection in a 1.3m commercial die; it is found to be substantial. Modelling of the die deformation using a commercial 3-D finite element package is described, with the load being based on a pressure field previously determined in the undeflected flow channel geometry. Prompted by unsatisfactory results, an algorithm is developed to evaluate the die body deflection iteratively, by coupling a 2-D thick plate analysis with the Hele-Shaw flow analysis, resulting in significantly improved results. Modelling of the conjugate melt flow/die heat transfer problem on the die cross-section is also carried out. Viscous heat generation, conduction and convection energy transport in the melt coupled with heat conduction in the die body are considered, together with the influence of electrical die heating and heat losses from the die surfaces by convection and radiation. Conclusions are drawn on thermal aspects of die design and operation. A graphical user interface embedded in Microsoft Windows is developed for a number of finite element codes, facilitating their use by non-specialists, and providing graphical displays of results. An outline of the operation of the complete package is described, including a convenient contouring algorithm.

No description available.

No description available.

No description available.

No description available.