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The approach adopted here has been to look for discontinuities in the deformation behaviour of UPVC and to attempt to correlate these with the brittle failure process. This approach has the premise that deformation and the initiation of the failure process have a strong interaction, i.e. one perturbs the other. Evidence to support this interaction in UPVC (and other glassy amorphous polymers) is abundant. The connecting link between deformation and failure could well be craze initiation and growth.

This research work focuses on the material characterisation of pultruded fibre reinforced composites for use in aggressive environments, including materials selection for physical properties, cost and durability. Consideration has been given to glass, carbon and aramid reinforcements, in conjunction with polyester, vinyl ester and hybrid resins. Interfacial strength, flexural strength and modulus were all investigated and characterised considering different levels of reinforcement up to a maximum of 85% by weight. On composite pultruded products water absorption deviated from 'Fickian behaviour' to an extent determined by temperature. The flexural strength, interlaminar shear strength (ILSS) and modulus measurements showed a strong dependence on moisture content, to a varying degree. With increasing reinforcement, flexural strength and modulus increased and the failure mechanism varied from compressive, to mixed compressive–tensile, to tensile, due to the environmental conditions. Conditioning of pultruded composite rebar in water illustrated that degradation occurs, accelerated by temperature.

The formation of stearate on precipitated calcium carbonate (PCC) and magnesium hydroxide has been examined. The object of coating the filler surface is to achieve improved mechanical properties in the resulting composite material. The coating of a filler with stearate allows the modification of the energies of interaction so as to improve dispersion and alter the mechanical properties of the interphase region. In this work the use of Fourier transform infra-red spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption isotherm analysis, thermal gravimetric analysis (TGA) and carbon–hydrogen–nitrogen combustion analysis (CHN) have been used to characterise the stearate on the surface of the calcium carbonate filler. New methods for the estimation of fractional coverage and coating thickness calculation have been developed. Using dynamic mechanical thermal analysis (DMTA) the effects of the coating on the interphase region of the composite have been demonstrated.

This thesis examines the effects derived from the ability of high pressure carbon dioxide to soften polymers. This has potential applications in the shape forming of polymers at lower temperatures, dye impregnation and the foaming of polymers. This study was conducted in two parts: (i) mechanical measurement of polymer softening under CO2 at high pressure; and (ii) foaming behaviour of polymers containing dissolved CO2 during depressurisation. In the first study the softening of polymers as a function of applied CO2 pressure and temperature was measured using a novel mechanical 3-point bend test rig. In initial experiments the temperature was slowly ramped upwards and the nominal glass transition temperature was recorded as where the central deflection suddenly begins to increase. Significant reductions in the bending onset temperatures were observed on the application of CO2 for polycarbonate, poly(methyl-methacrylate), glycol modified poly(ethylene-terepthalate) and polystyrene, of typically 50–100°C over the range of pressures applied (24 to 120 bar).

Energy transfer to molten flowing polymers has been studied. A comprehensive literature survey of heat transfer in non-Newtonian systems with particular emphasis to polymer melts has been described. Forrest and Wilkinson's theoretical treatment for evaluation of laminar flow heat transfer to non-Newtonian, non-isothermal, viscous fluids has been extended and modified by inclusion of thermal expansion effect in the energy equation. Resultant differential equations of change have been solved simultaneously for the following boundary conditions: (a) constant wall temperature; (b) constant heat flux; (c) arbitrary axial variation of the wall temperature.

Silane-crosslinked polyethylene was introduced for wire and cable insulations, and is now used extensively for the manufacture of domestic hot and cold water pipe systems. Silane crosslinking of polyethylene is a two stage processes, the first stage is the grafting of organosilane molecules onto polyethylene, and the second stage involves crosslinking through the alkoxysilane (Si-OCH3) groups to form siloxane (Si-O-Si) linkages. It is the grafting stage that influences the materials behaviour and therefore properties and performance of the crosslinked product. ISOPLAS crosslinkable polyethylene manufactured at Micropol Ltd has shown slight variations in measurable properties amongst materials processed in the extruders, which are determined using quality control tests in order to give a rough guide to the processability. Therefore, a detailed study was carried out to gain a better understanding of processing and structure-property relationships of the material.

Pure polyurethane dispersions (PUDs) have been synthesised via the prepolymer mixing method, with two different systems i.e. solvent free and the solvent containing PUDs. Isophorone diisocyanate (IPDI), polypropylene glycol (PPG 2000) and dimethylolpropionic acid (DMPA) were the basic materials. The prepolymers were neutralised with triethylamine (TEA) prior to dispersion into the mixture of deionised water and chain extender, hydrazine monohydrate (HYD). The same procedures were repeated in the making of the solvent containing PUDs with 20 wt. % of N-methyl-2-pyrrolidone (NMP). The film properties were examined with Fourier transform infra-red (FT–IR) spectroscopy, stress-strain tests, dynamic mechanical thermal analysis (DMTA), modulated temperature differential scanning calorimetry (MTDSC) and transmission electron microscopy (TEM). The latex particle sizes were measured with a Malvern Zetasizer. It was found that the plasticizing effect of NMP caused reduction in the glass transition temperature, Tg, which also affected the performance of the sample, particularly the tensile strength and extensibility. Annealing the solvent based PUDs under certain conditions improved the properties due to the evaporation of the NMP that was trapped in the films. The solvent-free samples showed superior properties to the solvent-based ones.

The thesis reports studies of cure kinetics and the glass transition temperature advancements of three commercial epoxy resin systems: MY 750 / HY 5922 (Vantico), MTM 44 -1 (ACG) and 8552 (Hexcel Composites). This investigation was conducted with the utilisation of Differential Scanning Calorimetry (DSC) and Temperature Modulated DSC (TMDSC). Appropriate phenomenological cure kinetics models were built to predict the degree of cure as a function of temperature/time profile. The validity of superposition of dynamic and isothermal experimental data was established. Rheological measurements were performed in order to determine the gelation region under given cure conditions. The cure modelling methodology was validated against an international Round-Robin exercise led by the University of British Columbia (Canada). The effects of carbon nanoparticle incorporation on the cure kinetics and the glass transition temperature advancement of two of the epoxy systems were also studied. Cure kinetics models were developed for the nanocomposites containing commercial multiwalled carbon nanotubes and a direct comparison was made with the models of the neat resin systems. The glass transition temperature advancement is shown to be affected in the early stages of the cure. The state of the dispersion of the nanoparticles was studied in order to correlate it with the observed effects upon the cure and on the morphology of the cured samples. The presence of carbon nanotube clusters is shown to have an influence on the phase separation in the MTM 44-1 resin system. As a potential industrial application of this study, optical fibre refractometers were utilised as an on-line cure monitoring technique. A good correlation was established between the measured refractive index changes during the cure and the degree of cure predicted by the above mentioned models, for the neat resin systems and their nanocomposites.