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Increasing scrutiny over industrial activity has driven the search for environmentally friendly processing alternatives. Supercritical (sc) CO2 functions as a transient plasticiser in polymer processing applications and offers intrinsic advantages. Exploiting the potential benefits provided by CO2 requires a detailed understanding of the implications of CO2 exposure to polymeric material. This thesis describes the use of the confocal Raman microscopy (CRM) and FTIR imaging to characterise polymers processed with scCOz. The processing of semicrystalline polymers is a complex process due to possible CO2-induced morphological alterations to the matrix. The development of an experimentalapproach for studying semicrystalline polymers processed with scCO2 via CRM, Ramanmapping and FTIR imaging is described. A significant gradient in the degree of crystallinity normal to the surface of poly(ethylene terephthalate) (PET) film has been observed non-destructively with CRM and confirmed by a complementary analysis of microtomed film sections via Raman mapping and transmission FTIR imaging. A model system of PET film impregnated with Disperse Red I (ORI) from a scCO2 solution was developed and a one-dimensional Fickian diffusion model was used to evaluate the diffusion coefficient of the dye as a function of pressure and temperature. This approach has been extended to investigate other scCO2 processed polymer systems including PET fibres, syndiotactic polystyrene impregnated with DRl and a biocompatible polymer impregnated with a model drug. The interdiffusion of polyvinylpyrrolidone and poly( ethylene glycol) subjected to scCO2 was studied using a novel application of in situ attenuated total reflection (ATR) FTIR imaging. Visualisation of the dynamic miscible polymer system was achieved and the influence of pressure and molecular weight elucidated, revealing the ability to control the rate of the dynamic process. The feasibility to apply in situ A TR FTIR imaging to study CO2-induced alterations in PET and CO2-induced polymer phase separation is explored.

Low molecular weight compounds were used to model the reaction between a range of substituted methyl-ketones with hydrazides in comparison to amines. The reactions were studied by 1H-NMR spectroscopy at three pH values, in order to establish structure-reactivity relationships and pH control of the reaction. The information gained was used to design four acrylate monomers containing a terminal methyl-ketone moiety. The monomers were incorporated into a methyl methacrylate and n-butyl acrylate polymer backbone at low concentrations. The methyl-ketone group was expected to engage in crosslinking reactions with a water-soluble dihydrazide crosslinker. Tests were performed to show the effect on polymer film properties when such a reaction occurs. Swelling studies were carried out to show the extent of reaction in polymer samples through calculation of the average molecular weight between crosslinks. Mc. An introduction to emulsion polymers and their application in binder compositions is given in chapter 1. Several condensation processes known to occur between carbonyl- and amino-functional groups in different structures, and under different conditions, are also outlined. The experimental procedures and analytical techniques used throughout the research are described in chapter 2. In chapters 3 and 4, model systems were used to determine details of the condensation process (in a dilute aqueous environment) and control of the reaction by pH. This knowledge was applied in chapter 5 to the design of polymer systems which may be crosslinked through such condensations. The resulting systems were compared to a commercially available crosslinking emulsion polymer composition to test their relative performance. These various aspects are discussed at the end of the thesis with suggestions for further research.

This thesis concerns the tensile strengths and Young's moduli of carbon fibres as they are affected by the conditions used to spin the polyacrylonitrile (PAN) precursor fibres. Particular attention has been given to factors affecting the strengths of the fibres since higher strengths would lead to increased impact resistance in carbon fibre reinforced plastics. Impurity particles in the PAN fibres were the main source of flaws in carbon fibres, with samples derived from PAF fibres spun under clean-room conditions having significantly higher strengths. For example clean PAN fibres stretched x 14 in steam gave carbon fibres with average strengths of 3.0 GN/m2 after heat-treatments to both 1400+/-C and 2500+/-C. When the PAN fibres were spun under normal laboratory conditions however the strength of the fibres after heat-treatment to 1400+/-C was only 2,1 GN/m2 and this decreased to 1.7 GN/m2 after treatment to 2500+/-G. Thus it was found that fls.ws due to impurities caused the average strengths of carbon fibres to decrease after heat-treatments to 2500+/-C and also to vary with the length of fibre tested. Following the analysis of samples of airborne dust, and experiments involving the deliberate contamination of PAN fibres before conversion to carbon fibres, it was concluded that the flaws were mainly caused by inorganic impurities such as silica, silicates and iron oxide. The flaws were thought to form in two stages (1) by reactions with the fibres leading to the reduction of the oxides and (2) because the impurities promoted the formation of localized randomly-oriented three-dimensional graphite in the fibres. The mechanical properties of the-carbon fibres were also found to be influenced by the amount of hot-stretch applied during the spinning of the PAN fibres and the hot-stretching temperature used.

The chemistry of the thermal reactions of polyacrylonitrile have attracted attention since the use of the polymer as a textile fibre. The discovery that high performance carbon fibres could be easily made from acrylic fibres added another dimension to the scene -the morphology of the fibres during the thermal reactions. This thesis attempts to combine chemical analysis with mechanical analysis in order to determine why acrylic fibres are so suitable for the formation of carbon fibres. Firstly, apparatus for the heat treatment and carbonisation of acrylic fibres was constructed, and experimental conditions for the production of high performance carbon fibres, from Courtelle fibres, were established and proved. By analysing Courtelle fibres taken from various stages in the production, the pertinence of the work was ensured. The analytical procedures used were elemental, infra-red and mechanical. Because the spectrum of Courtelle was complicated by the comonomers, which contained oxygenated groups, the homopolymer was synthesised and used for comparison. Additionally, in order to obtain quantitative measurements from the infra-red spectra, films of homopolymer and Courtelle were produced and a technique for correlating fibres and film was developed. The work was concentrated on the preliminary stages of the heat treatment process where the foundations of the carbon fibre structure are laid. The most important result of this work is that reasons have been described for the necessity of the oxidation stage in the production. These reasons centre on the formation of high energy bonding and the introduction of potential cross-linking ability, both without disruption to the oriented macromolecular structure. This thesis also points out the more significant anomalies in the theories. Perhaps the least understood area is the relation between the extent of precursor oxidation and the development of high performance properties in the carbon fibres. It seems appropriate to finish this summary on a negative note as although the suggested theories seem basically sound, the anomalies are of such gravity that it would be conceited to say that the process of producing carbon fibres from acrylic fibres, is well understood.

The microstructural reorientation occurring during annealing of various grades of oriented high-and low-density polyethylenes was examined using wide and low angle X-ray diffraction. The differences in the degree of reorientation were interpreted in terms of the relative crystallinities of the different grades. Differential scanning calorimetry was used to relate the melting behaviour of the specimens to their structure. Drawing at elevated temperatures resulted in specimens with a particularly simple texture where the stacks of lamellae were inclined with their normals aligned parallel to the drawing direction. Specimens with this initial texture were annealed and their elastic constants determined by ultrasonic techniques. A study of four different ultrasonic techniques was made to determine their relative accuracy and reproducibility in measuring the velocity of stress waves in oriented polyethylene. The highly anisotropic nature of the specimens led to diffraction and dispersion effects, with the result that two of the techniques were found to be unsuitable for oriented systems. The symmetry of the drawn and annealed specimens was found to be approximately hexagonal rather than orthorhombic. The value of the elastic constant was shown to increase with draw ratio to over 70 GPa for draw ratios of x25. After annealing at temperatures approaching the melting point, the value of C[33] fell to about 10% of its as-drawn value. This behaviour is correlated with the loss of orientation of the molecules in the amorphous phase during annealing. The elastic constants C[11], C[22], C[44] and C[55] were comparatively insensitive to changes in molecular orientation. A simple structural model was proposed and developed and its elastic constants evaluated. The experimentally measured elastic constants were compared with the model elastic constants by using theoretically determined values of the elastic moduli of polyethylene crystals in the expressions developed to describe the elastic properties of the model. Good quantitative correlation was found between the predicted and measured elastic constants, taking into account their relative crystallinities.

The properties, classification and fabrication of plastics are first reviewed with a description of the different polymers. The consumption pattern and uses of plastics are then described. In Chapter 4 the output of solid wastes, their weight, volume and nature are discussed. Estimates of solid wastes production for 1974/75 are calculated. The first part of Chapter 5 reviews plastics waste forecasts made by Staudinger, and the second part describes the development of a model for forecasting plastics wastes and a discussion of results obtained. The next three chapters describe the various collection, transport, and disposal methods used and proposed for solid wastes, their costs, and the effect of plastics waste on them. Separation plants are also discussed. The various methods and techniques which are/would be involved in the recycling of plastics waste is reviewed in Chapter 9, and the various methods of rendering plastics degradable in Chapter 10. Chapter 11 is an analysis of the litter problem. The current state of knowledge is discussed, and a model is described, which can be used to study the effect of various parameters on the litter level. Finally, alternative policies for dealing with plastics waste are discussed.