No description available.

Plasticised poly(vinyl chloride)(PVC-P) remains the most widely used bloodcontacting biomaterial. With respect to the blood compatibility of PVC-P, the plasticiser plays a more important role than the PVC polymer itself, since the blood contacting surface is highly distributed with plasticiser. Therefore, the objective of this project was to study the significance of the plasticiser on protein adsorption onto PVC-P, where the features of plasticiser considered were plasticiser selection (nature of plasticiser), the plasticiser surface level and plasticiser surface distribution. To evaluate this, three types of medical grade PVC-P, plasticised with 2-diethylhexyl phthalate (DEHP), tri-(2-ethylhexyl) trimellitate (TEHTM) and n-butyryl-tri-n-hexyl citrate (BTHC) respectively in sheet form with the same softness, were selected. Protein adsorption was carried out using 1251 radiolabelled human fibrinogen and bovine serum albumin. The in vitro protein Imaterial contact was achieved with a modified 24-well incubation test cell. A reduced plasticiser surface level was obtained with methanol surface treatment. Surface characterisation was carried out using ATRFTIR and UV-spectrophotometer. Results obtained indicate that fibrinogen adsorption on PVC-P strongly correlates with the plasticiser surface level. A reduced plasticiser level can reduce fibrinogen adsorption and increase albumin adsorption. However, excess surface washing might lead to a surface topographical change, initiating an increased fibrinogen adsorption. Protein adsorption is also dependent on the plasticiser nature and plasticiser surface distribution. A high level of plasticiser does not necessarily mean a high reactivity towards fibrinogen adsorption. Based on this study, surface modification of PVC-P was carried out using cyclodextrins (CDs) by blending. The combination of CDs with polyethylene oxide (PEO) or polyethylene (PEO)-poly(propylene oxide) (PPO) triblock copolymer (pluronic surfactant) was also studied. Protein adsorption results indicate that the surface enriched CDs, CDIPEO, CD/Pluronic physical mixture or CD inclusion complex (CIC) can achieve a reduced protein adsorption. Finally, a possible mechanism was hypothesised and a proposal was made for a novel form of surface modification.

The study reported in this thesis investigates the relationships between the morphology of PEI/epoxy blends reinforced with glass fibres and their fracture properties. Hot stage optical microscopy is used to study the phenomenon of phase separation in the thermosetting blends in the presence of glass, carbon and aramid fibres. Phase separation is shown to be unaffected by the presence of aramid and carbon fibres, but is affected by the presence of glass fibres, to a degree which mainly depends on the PEI concentration. Other parameters like cure temperature, the nature of the glass fibre surface and fibre volume fraction are also examined. The most striking feature is the initiation and development of an epoxy-rich layer around the fibres for blends modified with 15 wt % PEI. This concentration corresponds to a co-continuous network of PEI-rich particles embedded in an epoxy-rich matrix. The effects of morphologies formed during phase separation on the fracture properties of glass fibre-reinforced composites are studied using the mixed-mode bending test rig developed by NASA. Extensive scanning electron microscopy (SEM) observations provide qualitative support to the delamination results. They show that different micro-mechanisms of deformation can occur, depending on the matrix microstructure and the fibre/matrix interfacial strength. SEM observations show that cusps are not only present under mode II loading, but also under mixed-mode I/II loading. They reveal that the spatial density and angle of cusps depend on the applied loading mode, the interfacial strength and the nature of the matrix itself. These observations are the base of a model which describes the delamination behaviour of composites from pure mode Ito pure mode II loading.

No description available.

The synthesis and properties meta and para poly(ethylene oxybenzoate)s, two semi-crystalline polymers, are reported. It is found that by copolymerising equimolar quantities of meta and para monomers amorphous polymers are produced which are significantly more soluble than their respective homopolymers. The effects of introducing an AB(_2) branching agent (A) into p-PEOB are also considered. It is found that the relationship between Tg and molecular weight does not vary significantly with the extent of branching. Using the data obtained from DSC experiments, a linear relationship between the melting temperature and the branching composition of p-PEOB is reported up to a critical value of 12.5mole% of A, above which materials are amorphous and chloroform soluble. A general technique for measuring number average molecular weight of branched materials, using (^1)H NMR end group counting, is described. This is used successfully in the analysis of p-PEOB copolymers with less than 15mole% branching. Molecular weights of the amorphous materials, i.e. with extents of branching in excess of 12.5mole%, are measured using conventional GPC with respect to linear polystyrene equivalents. Relationships between the extent of branching, log Mw and log [n] in chloroform, appear to be linear for amorphous copolymers with branching compositions of between 20mole% and 100mole%. A detailed analysis of carbonyl signals in (^13)C NMR spectra of these materials is reported, which provides evidence that the copolymerisations are statistical and not selective.

Fibre-reinforced composites usually exhibit anisotropy of thermal as well as mechanical properties. For example, in a unidirectional carbon fibre-reinforced plastic of 60% volume fraction, the longitudinal thermal conductivity may be greater than that in the transverse direction by a factor of 50, and greater than that of the unreinforced polymer by more than two orders of magnitude. In order to evaluate the engineering applications of thermal anisotropy, this thesis concentrates on the development and validation of a generalised finite element model of heat conduction in an anisotropic medium. This uses a variational formulation of the anisotropic time-dependent heat conduction equation, and is implemented for two and threedimensional quadratic finite elements. The model may be used for the solution of problems having any combination of steady or time-dependent boundary conditions (fixed temperature, convection, radiation, heat flux and internal heat generation), as well as nonlinear properties. Anisotropy is specified by the components of the two or threedimensional thermal conductivity tensor; efficient representation of nonhomogeneous materials is achieved by the specification of properties at element integration points. Theoretical validation of the model is carried out by means of a number of mathematical solutions to orthotropic and anisotropic problems. Experimental validation is performed by comparison of calculations with measured steady-state surface temperatures on a cylindrical specimen of unidirectional carbon fibre-reinforced epoxy resin. The thermal property data for this exercise are obtained from measurements of principal thermal conductivities on absolute and comparative steady-state apparatus. The use of the finite element model in two industrial applications is briefly described. These concern thermal cycling during composite fabrication with reinforced thermoplastic tape, and an analysis of heat transfer in a composite propeller blade.

Fibre composite hybrid materials are generally plastics reinforced with two different fibre species. The combination of these three materials (in this thesis they are carbon fibres, glass fibres and polyester resin) allows a balance to be achieved between the properties of the two monofibre composites. Over the fifteen years since the introduction of continuous carbon fibre as a reinforcement, there has been considerable speculation about the "hybrid effect", a synergistic strengthening of reinforced plastics with two fibres when compared with the strength predicted from a weighted average from the component composites. A new equation is presented which predicts the extent of the hybrid effect. Experiments with a variety of carbon-glass hybrids were undertaken to examine the validity of the theory and the effect of the degree of inter-mixing of the fibres. The classification and quantification of the hybrid microstructures was examined with a view to crosscorrelation of the intimacy of mixing and the strength. Mechanical tests were monitored with acoustic emission counting and acoustic emission amplitude distribution equipment. Some specimens were subjected to one thermal cycle to liquid nitrogen temperature prior to testing. Fracture surfaces were examined in the scanning electron microscope. Numerical analysis by finite element methods was attempted. A constant strain triangular element was used initially, but in the later analyses the PAFEC anisotropic isoparametric quadrilateral elements were used. The system was adapted so that a \Ir singularity could be modelled, and post processor software was written to allow nodal averaging of the stresses and the presentation of this data graphically as stress contour maps.

No description available.

This study is concerned with the development of micro-thermal analysis as a technique for characterising heterogeneous polymers. It is divided into two main parts. In the first part, the use of miniature Wollaston wire near-field thermal probes mounted in an atomic force microscope (AFM) to carry out highly localised thermal analysis (L-TA) of amorphous and semi-crystalline polymers is investigated. Here, the temperature of the probe sensor or tip is scanned over a pre-selected temperature range while in contact with the surface of a sample. It is thereby used to heat a volume of material of the order of several cubic micrometres. The effect of the glass transition, cold crystallisation, melting and degree of crystallinity on L-TA measurements is investigated. The materials used are poly(ethylene terephthalate), polystyrene and fluorocarbon-coated poly(butylene terephthalate). The primary measurements are the micro- or localised analogues of thermomechanical analysis (L-TMA) and differential thermal analysis (L-DTA). The effect of applying a sinusoidal modulation to the temperature of the probe is also investigated.

Moisture effects on glass-reinforced-plastics have been investigated using a stress-rupture approach, Stress-rupture data for a powder- bonded E-glass chopped strand mat/polyester laminate was obtained for the following environments; 1) 5% RH; 2) laboratory conditions; 3) Water at room temperature; 4) water at 40°C; 5) IN hydrochloric acid Stress-rupture data for an emulsion bonded E-glass chopped strand mat/polyester laminate was obtained for laboratory conditions and water at room temperature. The effects of loading histories and porosities of up to 3% were also investigated. Failure mechanisms were investigated by scanning electron microscopic examination of the fracture surfaces, residual strength measurements and optical examinations before and after a resin burn off. Three failure mechanisms were shown to operate over the test period. The most common was caused by environmental stress corrosion of essentially pristine fibre lengths. In water at 40°C an additional strength loss was caused by interfacial degradation. The emulsion bonded mat laminate in water at room temperature exhibited a steeper stress-rupture curve due to the increased permeability of the matrix in the interfilament channels Surface damage was also noted for all the aqueous environments. The duration of the tests was, however, too short for the damage mode to influence the stress-rupture curves.