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Machining is a non-linear process and involves the consideration of variables such as inelasticdeformation, high temperatures and contact conditions. This thesis focuses on investigating thecontact conditions between cutting tools and polymeric materials during orthogonal cutting. Atest rig has been developed to allow cuts to be taken from a rectangular workpiece, such that therake angle (the angle of inclination of the tool surface) can be varied. In this work the rake angle was varied from -20o to 30o, and the cutting was performed at ratesof 0.01ms-1 and 0.1ms-1 on PMMA, nylon 4/6 and nylon 6/12. As part of a round robininvestigation, tests were also performed on HIPS, ABS and LLDPE.The experimental method developed required the measurement of forces in two directions (thedirection of cutting, Fc and transverse to the direction of cutting, Ft). The rig allowed for thecareful control of the depth of cut, h. After each cut, the thickness of the off-cut chip hc wasalso measured. A series of cuts were taken at depths varying between the range of 0.02mm to 0.25mm and theforces were measured. A cutting theory has been applied to the experimental data to determinethe fracture toughness Gc, and the yield stress ?Y of the material. The Coulomb friction ? andan adhesion term, Ga representing sticking at the tool-chip interface, were also deduced. Independent fracture mechanics tests were performed at a range of temperatures and rates on thedifferent polymers. Tensile tests were also performed, to compare standard values to thematerial parameters determined in cutting. The values of Gc and ?Y deduced were independentof the rake angle however, ? and Ga were not. The calculated values of Gc were typicallywithin 5% of the standard values however, ?Y was found to be up to 5 times higher. Theexistence of work hardening is believed to be the cause of these elevated values. The cutting analysis was also applied to some previously published metal cutting data andproduced constant values of Gc.

No description available.

Plastic pipeline systems have now become dominant for fuel-gas and water distribution networks. Although they have an impressive service record failures do occur, with Rapid Crack Propagation being characterised as the least probable but most potentially catastrophic one. This study investigates the effect of structural morphology and bulk residual strains on the RCP performance of polyethylene pipes, and proposes a new methodology for predicting a safe service envelope. During crack propagation in PE pipes, the fracture surface has two distinct regions; plane strain and plane stress. In addition to the Instrumented Charpy, Reversed Charpy, High Speed Double Torsion, Dynamic Mechanical Analysis and uniaxial tensile testing, S4 tests of extruded pipe specimens were employed in order to evaluate the structural and fracture parameters of pipe grade resins in these two fracture modes on pipe. A new experimental technique, which modified the pipe bore crystallinity without altering the residual strain field (as evaluated from slit ring tests) showed that the bore surface layer properties had much less influence on RCP than previously thought. Parallel with the experimental work, modeling of the fracture mechanisms was also undertaken. Using previous models in the field, such as the adiabatic decohesion model, the plane strain fracture toughness was evaluated while the plane stress fracture toughness was evaluated either from the Reversed Charpy or from the stability of adiabatic drawing in a tensile test. A mixed mode, temperature sensitive toughness was finally evaluated, leading to an overall fracture properties assessment for polyethylene pipes which could be compared directly to the crack driving force during RCP in pipe. By employing a new mathematical approach, which incorporated both the effects of residual strains and pipe stiffness behind the pressure decay length, a previous basic analytical RCP model was further developed and compared to more elaborate finite element and finite volume solutions. The new results were also compared to S4 experiments using high-speed photography and showed that the new methodology could be employed by the end user even when testing facilities are not directly available

This thesis describes the development of a new method to confer degradability to water soluble polymers already used in the oil servicing industry. Generally, high molecular weight polymers with a C–C backbone, like vinyl polymers, tend to be resistant to hydrolysis, oxidative cleavage, enzymatic attack, etc., and therefore they are not degradable, whereas hetero-atom-containing polymer backbones like esters, carbonates, amides, anhydrides, phosphazenes, etc. confer degradability. Redox polymerisation was chosen to introduce labile links into the hydrocarbon backbone of vinyl polymers. A variety of reducing agents that could be chosen provides a platform of polymers that can degrade upon experiencing different triggers. A redox pair consisting of reducing agents such as triblock copolymer poly(lactic acid)-b-poly(ethylene glycol)-b-poly(lactic aicd), polycaprolactone diol, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and L-cystine and oxidising ceric (IV) ions were used to initiate redox polymerisation of acrylamide, N,N-diamethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid. The presence of degradable groups in the polymer backbone was studied using FT-IR, NMR and DSC. The degradation behaviour of the synthesised polymers was investigated by GPC. The polymer degradation was triggered in different ways dependent on the labile group which was incorporated into the polymer backbone. Drag reduction properties were quantified using a standard rheometer equipped with a double-gap measuring geometry, by calculating percentage of drag reduction (%DR) based on apparent viscosity. From the obtained results it is clear that redox reaction between a reducing agent and oxidising metal ion can be used to initiate polymerisation of vinyl monomers, nevertheless not all the systems proved to be equally successful. It was found that using a water soluble and hydrolytically stable reducing agent containing azo functionalities gave the best results and multiple labile groups were incorporated into the polymer backbone. Polyacrylamide with azo-links in the backbone proved to be as good drag reducing agent as polyacrylamide synthesised by initiation from the poly(ethylene glycol)/Ce(IV) redox couple, however it lost its drag reduction properties once subjected to elevated temperatures. From the carried out studies it seems that triblock copolymer poly(lactic acid)-b-poly(ethylene glycol)-b-poly(lactic acid) is not an appropriate reducing agent due to its low stability in water at low pH. H1-NMR spectra show that the reducing agent degrades during the course of the polymerisation and hence cannot be used in aqueous environment to incorporate degradable groups into the polymer. In order to use a more stable but hydrophobic polyester - polycaprolactone diol, micellar polymerisation was utilised. The results showed that using redox polymerisation amphiphilic copolymers can be obtained. It was confirmed not only by H1-NMR, FT-IR and DSC, but also by the fact that hexane/water emulsions could be stabilised by acrylamide initiated from polycaprolactone diol.

Emulsion templating using high internal phase emulsions is an effective route to prepare low density, high porosity macroporous polymers known as polyHIPEs (poly(high internal phase emulsion)). Conventional polyHIPEs, synthesised from surfactant stabilised w/o (water-in-oil) emulsions, have low permeabilities and poor mechanical properties. This thesis describes an investigation into developing and characterising one type of tough and permeable macroporous polymers via emulsion templating. Increasing the continuous phase volume from HIPEs (high internal phase emulsion) to MIPEs (medium internal phase emulsion) is an effective way to improve the mechanical properties of resulting macroporous polymers. The influence on morphology and physical properties of the resulting macroporous polymers caused by the usage of different initiators and surfactants in MIPEs was initially discussed to optimise the formulation of MIPEs based on styrene and divinylbenzene (DVB). The MIPEs based on styrene and DVB used azobis(isobutyronitrile) (AIBN) as initiator produced macroporous polymers possessing desired open porous interconnected pore structure no matter which surfactant (surfactant mixture) was used while potassium persulfate (KPS) and redox initiator system cannot produce open porous macroporous polymers from MIPEs consisting of styrene and DVB. Then tough and permeable low density polymers were developed, produced by polymerising the continuous phase of emulsion templates, which contained styrene, polyethyleneglycoldimethacrylate (PEGDMA) and silylated silica particles. PEGDMA and the silylated silica particles acted as crosslinker. The functionalised silica particles were incorporated into the polymer, which resulted in a significant improvement of the mechanical properties of the polyHIPEs without affecting the interconnected and permeable pore structures. The physical and mechanical properties of the tough and permeable macroporous polymers were characterised. Especially the mechanical properties, including shear properties and fracture toughness (mode II) were investigated using the Arcan fixture. Both the shear properties and fracture toughness (mode II) increased significantly with increasing the organic phase volume in emulsion templates and the further improvements can be obtained by the incorporation of silica filler in the emulsion templates. Finally, approaches to directly synthesise hydrophilic macroporous polymers based on styrene and DVB were presented since most of macroporous polymers produced from HIPEs are hydrophobic and need modification after polymerisation to improve the surface wettability. The incorporation of silylated silica particles in the emulsion templates improved the wettability of the resulting macroporous polymer but not the water uptake. The water uptake of macroporous polymers can be increased by the introduction of methacrylic acid (MA) and dimethylaminoethyl methacrylate (DMAEMA) into the aqueous phase of emulsion templates as additional monomers in order to synthesise hydrophilic polymer/polymer macroporous composites.

The primary aim of this research was to identify a novel process for the manufacturing of UHMWPE fibres and coating. Due to the high molecular weight of UHMWPE, it cannot be converted into fibres by standard extrusion processes it must be firstly dissolved in hydrocarbon solvents such as decalin, kerosene etc, which are unsustainable and potential hazards (to environment and human), then extruded to form a gel fibre. Following the extrusion process the solvent must be removed which involves the use of a secondary solvent e.g. n-hexane, toluene etc. which themselves are potentially hazardous. Research revealed that terpene, a waste product of the orange juice industry was suitable substitute for the currently used solvents. Gel produced as a mixture of UHMWPE and terpene was successfully converted into fibres and fabric coatings. However, the ram process was initially found to be problematic, which was due to the presence of entanglement of the polymer chains. This was resolved by applying acoustic energy to the gel, which optimised the chain alignments thus reducing entanglement and allowing a consistent fibre to be ram extruded. The terpene based extrusion process designed in this research eliminated the solvent removal stage, which eliminated the use of secondary solvent thus eliminating the hazards and cost associated with it. Since the process does not involve a separate solvent removal stage, it has the potential of reducing the processing cost. The terpene also allowed a consistent UHMWPE coating to be applied to the cotton fabric. The coated fabrics showed a good resistance to highly concentrated acids, indicating the potential application of such coatings as protective apparel in the areas involving concentrated acid e.g. liquid acid battery, fertilizer industry, iron and steel making industries where acids are widely used. The coating process developed in this research has expanded the use of UHMWPE beyond the current possibilities.

Three commercial clays: Cloisite Na+ , Cloisite 30B and Cloisite 15A were used to melt compound with a number of polymer matrices, including polypropylene (PP), poly(butylene terephthalate) (PBT) and polyamides (PA). X-ray diffraction (XRD), contact angle measurement and thermogravimetric analysis (TGA) showed small interlayer space, poor compatibility and low thermal stability of these nanocomposites, resulting in poor mechanical properties in composites. A number of modifications of commercial clays were carried out, including silylation and introduction of thermally stable surfactants, e.g. alkyl quaternary phosphonium cations and polyhedral oligomeric silsesquioxane (POSS). It was found that poor compatibility between polymer matrices and organically modified clays, especially in those POSS modified clays, again restricted the formation of exfoliated structure in polymer matrices. A mode of dual-surfactant modification for clay was developed, and large interlayer spacing (>3.2 nm), good thermal stability (decomposed at ~300°C) and improved surface properties for those dual-surfactant modified clays promoted a better dispersion of clays in polymer matrices and consequently better mechanical properties. For example, the tensile moduli of PP, PBT and PA 12 were improved from 515 MPa, 1065 MPa and 490 MPa to 1020 MPa, 1470 MPa and 800 MPa of their nanocomposites containing 3 wt% dual-surfactant modified clays, respectively. However, the dispersion of these organoclays varied in different polymer matrices, due to the different compatibility and the existence of polar type interactions between organoclays and polymer matrices. In order to further address the effect of polymer matrix on clay dispersion, three polyamide matrices (PA 6, PA 11 and PA 12) were employed, and PA 6 based nanocomposites showed the most effective exfoliation and mechanical enhancements due to the strong polar type interactions between the polymer and the organoclays.

The fracture and mechanical properties of an epoxy resin system have been investigated as a function of changes in stoichiometry and heat treatment. Relationships between the various macroscopically measured properties and the microscopic characteristics of the cured resin are described. The investigation shows that the concept of fracture surface work, γ , measured by a cleavage technique, is a sensitive parameter for monitoring changes in the resin's fracture properties and that the Irwin-Kies and Berry analyses can provide a more sensitive monitor of γ than the Gurney method, in some circumstances. The investigation also demonstrates how the elastic and visco-elastic properties of the resin can effect plasticisation at the tip of a crack, with consequent improvement in fracture toughness. To aid the interpretation of the mechanical data, a morphological characterisation of the cured resin will be described in which quantitative infrared spectroscopy, thermo-mechanical analysis, solvent. uptake resistance, chemical and ion-beam etching methods have been used.

The work presented in this thesis is centered around the development of optical tweezers as a tool for the manipulation of block copolymer nanostructures. We show how optical manipulation can be used to control the solution behaviour of a variety of nanostructured materials formed by self-assembly, enabling their patterning or the formation of novel hierarchical assemblies. Furthermore, we show how arrays of block copolymer nanostructures can be used as nucleation sites for the surface-directed self assembly of additional block copolymers and for the templating of functional materials.