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The use of pyrolysis as a waste disposal method for waste plastics has been well established. However, the market value of the recycled plastic products and separate upgrading of the pyrolysis product liquid are some of the challenges facing the process. Therefore, the use of pyrolysis-catalysis of waste plastic in a two-stage pyrolysis-catalysis reactor system could bring a balance between sustainability and market value of the products generated. Hence, this work investigated the influence of different types of zeolite catalysts on the pyrolysis-catalytic upgrading of waste plastics for quality liquid fuels and valuable chemical production. Initially, two zeolite Y and ZSM-5 catalysts, in the form of pellets, were used for pyrolysis-catalysis of WEEE. Zeolite catalyst with a lower Si-Al ratio (Y zeolite) produced a higher conversion of the styrene to other aromatic products, particularly benzene and toluene. Thereafter, the influence of six zeolite catalysts with different surface areas and Si: Al ratios was investigated on the catalytic pyrolysis of waste high-density polyethylene (HDPE). Overall, the results suggest that the catalyst properties influenced the conversion of HDPE to more valuable products such as fuel-range hydrocarbons and chemicals. Similarly, pyrolysis of real-world mixed plastics, simulated mixed plastic (SMP), and virgin plastics were investigated in the presence of HZSM-5 catalyst. In addition, a sample of spent FCC catalyst was also tested for the pyrolysis of the plastic samples. Finally, the influence of spent FCC, fresh zeolite Y and ZSM-5 catalysts was investigated under different bed temperatures from 400 – 600 °C. This final work confirmed that the choice of a bed tempetrure of 500 °C, for most of this research was appropriately justified. Overall, the product oils gave fuel properties similar to gasoline, the aromatic content of the oil make them suitable as chemical feedstocks, the gas products with very high-calorific values can be used as fuel gas.

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In recent years, there has been a growing incentive towards production and application of environmentally benign materials with properties similar to those obtained from irreplaceable resources or exhibiting harmful effects on the environment. In this respect, bioplastics have gained attention in quest of materials that can be used in place of conventional petro-chemical plastics. Biocompatibility, biodegradability and compostability of bioplastics are among the most favourable characteristics of the materials mostly derived from biological systems. Polyhydroxybutyrate (PHB) is a fully biodegradable bioplastic with similar physical properties to polyethylene and promising applications in various commercial fields including automation, aviation, medication, nutrition, fuel, packaging and many more. PHB production with Mixed Microbial Cultures (MMC) has recently gained attention as a cost effective production strategy by using bacteria that adapt with complex substrates presented in inexpensive waste materials. The initial research motivation was to enhance PHB production operation by means of the solutions obtained from sophisticated mathematical algorithms used for process optimisation. For this aim, a computer-based program simulating PHB batch process with MMC which was successfully validated with experimental data was available. Since mechanistic models of the simulation program could not be applied in optimisation algorithms, accurate empirical models were required. In the quest for reliable and accurate empirical models that can predict product concentration at the final stage of a batch operation, a methodology was developed in this study for classification of the batch operational regions based on the PHB critical process attributes. In the core of this research work, an innovative systematic methodology improves process understanding towards advanced process monitoring and control. This method enables operational scrutiny for generation of process knowledge regarding PHB process using MMC. The qualitative info-illustrations produced in the course of the classification method provide a sound platform for generation of considerably more accurate (quantitative) empirical models. These empirical models will be used in process optimisation studies. Abstract III In this research, PHB production occurs in a process type known as “feast and famine” or as “aerobic dynamic feeding” which is a well-known strategy applied for bacterial production with MMC. The “feast and famine” operations take place in Sequential Batch Reactors (SBR) in order to assure occurrence of the “feast” and the “famine” phases intermittently in each operational cycle. While PHB formation occurs during the “feast” phase, a “famine” phase should be followed to cause a cell physiological adaptation to maintain PHB production capability of bacteria. Establishment of the analytical methodology developed in direction of process empirical modelling realisation enables prediction of “feast” and “famine” phase occurrences based on the batch initial state documented for the first time in this work. This mathematical equation (“Phase Differentiating Equation”) plays a significant role in development of a novel SBR recipe for production of PHB with MMC. Execution of the recipe by the PHB process simulation program demonstrates high reliability of the proposed recipe. Application of the “Phase Differentiating Equation” in the SBR recipe assures favourable occurrence of the “feast” and “famine” phases in the majority of operational cycles. Reduction of operational failure rate reduces PHB production cost to improve its market position. The SBR recipe structure consists of six-stage cycles including (1) “feast” phase preparation stage, (2) “feast” phase operation, (3) operational quiescence, (4) product exploitation, (5) “famine” phase preparation stage and (6) “famine” phase operation. Operational reliability is investigated along with load disturbance rejection embedded in the SBR recipe. At the end, Sequential Quadratic Programming (SQP) is applied successfully as an optimisation algorithm to maximise PHB production under operational constrains.

It has been hypothesised that weight reduction in ropes can be realised by the hybridisation of steel strands with non-metallic carriers in order to improve the efficiency of hoisting processes, most notably in mining applications. While this has been attempted by replacing steel central wires with unreinforced polymers and parallel fibre cores, this investigation has considered the replacement of steel wires with carbon fibre reinforced plastic rods. Fibre reinforced plastics are valued for their high strength-to-weight ratios and ubiquity. Since load sharing is maximal between materials of similar stiffness in a hybrid system, high strength carbon fibres were identified as the most feasible reinforcements for achieving compatible mechanical properties with those of high strength steel wires. A nylon polymer matrix was chosen to provide a reasonable balance between toughness, environmental stability and cost. A pultruder was designed and constructed in order to produce carbon fibre/nylon 12 rods for the creation of novel steel/CFRP hybrid strands. Development of the pultruder highlighted challenges in manufacturing that have been solved for industrial processes but remain underrepresented in academic research. Cost effective and flexible laboratory-scale techniques included fibre spreading by rollers, powder impregnation and the use of heating strips. Superior consolidation of the polymer matrix was obtained in rods pultruded from commingled stretch-broken carbon fibre/nylon tows, which emerged as the most appropriate feedstock. The Young's modulus and tenacity of hybrid carbon fibre/vinyl ester central rods were found to exceed that of standard steel strands, which in turn were higher than that of hybrid strands produced with in-house pultruded rods. Although this identified a need for the refinement of manufacturing conditions, it identified a lower bound of material properties required of the central rod in order to improve the tenacity of a hybrid strand. The finding of higher tenacity for the hybrid carbon fibre/vinyl ester strands demonstrated the feasibility of hybridising steel wire strands with non-metallic rods as a novel means of increasing the strength-to-weight ratio of strands. Finite element modelling of strands with a range of non-metallic core materials confirmed the material selection process by predicting the suitability of carbon fibre reinforced plastics over other core materials in improving the tenacity of hybrid strands.

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Synthesis and properties of various novel polyurethanes (PUs) and poly(urethane ureas) (PUUs) were investigated. The formation of PU prepolymer in bulk was investigated via in and ex situ Infrared spectroscopy to obtain rate constants for various diisocyanates reacting with poly(tetramethylene oxide) (PTMO). PUUs were prepared from PTMO and a modified polyether containing methyl side groups. The introduction of methyl side groups into the polyether reduced the crystallinity of the PUUs and increased both flexibility and phase separation. Several attempts were made to prepare liquid crystalline PUs via mesogenic diols. Via differential scanning calorimetry and polarised optical microscopy the crystallinity and melting temperature of these PUs were found to increase with increasing rigidity of the mesogenic diol. The nature of the hydrogen bonding, as observed by Infrared spectroscopy, was primarily dependent on the nature of the diisocyanate. Through a combination of two diisocyanates with a mesogenic diol a new enantiotropic liquid crystalline PU was successfully prepared. The synthesis of poly(lactic acid) oligomers was optimised to improve their suitability as a precursor for PUs. Quality of the oligomers, in terms of MW and end group control, could be improved through polycondensation in solvent with molecular sieves or via solid state polymerisation.

Polypropylene films are widely used as packaging materials for foodstuffs, since they offer excellent barrier properties against polar substances, high elasticity, mechanical strength, transparency and chemical stability. However, the relatively low surface energy of polypropylene represents a major issue for the adhesion of printing inks and labels. To improve printability it is necessary to perform a surface activation process. In the presented work, the atmospheric pressure dielectric barrier discharge (DBD) in nitrogen is investigated as a surface treatment method to increase the surface energy of biaxially orientated polypropylene foils. This technology creates a non-thermal plasma by applying strong electrical fields to a gas between two electrodes. The reactive species of the plasma forms new electronegative chemical groups on the surface and also etches the surface of the substrate. Both effects lead to an increase of the surface energy of the plasma treated polymer films. The crosslinking of polymer chains is also a possible effect caused by the plasma treatment. A new plasma rig was designed for this project, including a closed plasma chamber, two different parallel electrode configuration (flat or sawtooth electrodes) and a reel-to-reel system for the transport of the polypropylene foil. The designed system allows to adjust the sizes of the gas gap and the thickness of the dielectric. In addition, the plasma chamber can be filled with every gas or gas mixture wanted. A D-optimal design of experiments approach was utilised to study the influence of the power applied to the electrodes, the size of the gas gap and the thickness of the dielectric on the wettability of the treated polymer films. Furthermore, a flat electrode and a sawtooth electrode configuration are compared to each other. The findings of this work clearly indicate that the sawtooth electrode configuration is superior regarding the consumed electrical power and the wettability of the treated films. The optimal setting for the plasma treatment with the sawtooth electrode configuration are a low gas gap and a high power applied to the electrodes. The thickness of the dielectric has no influence on the wettability of the treated film. However, the increase of the dielectric thickness leads to an increase of the consumed power. These findings were transferred to an industrial process, where the polymer foils were treated in a nitrogen atmosphere with admixtures of CO2, N2O and C2H2 in the ppm range under the founded optimal conditions. A significant difference in the surface energies of these samples could not be identified by contact angles measurement, but all samples showed a significantly reduced hydrophobic recovery rate in comparison to samples treated by the in the industry more conventional plasma treatment in air. The DBD surface treatment in nitrogen is therefore an important improvement for the industrial production, because the treated packaging foils can be stored longer before they are processed further without the need to refresh the surface treatment. The low hydrophobic recovery of the samples treated in the nitrogen plasma is connected to an intensified crosslinking of the polymer chains on the surface of the treated polypropylene films.

Polyethylene (PE), particularly linear medium density PE (LMDPE), is the most widely used thermoplastic in the rotational moulding (RM or rotomoulding) industry, possessing a balance between melt flow characteristics and mechanical properties best suited to the RM process relative to alternative thermoplastics. Reliance of the RM industry on LMDPE limits the application envelope for manufacturers due to the inherently low modulus of the material; manufacturers overcome this low modulus by increasing the wall thicknesses of their products which is costly and energy intensive. The addition of filler particles to PE as a method of modulus enhancement was considered a feasible alternative to increasing the wall thickness. The resulting composite material could down gauge part thickness and potentially expand the application envelope of RM. Phase 1 of this study observed the behaviour of RM grade PE’s with the introduction of filler particles in order to double the modulus (namely garnet, sand, cenospheres or fly-ash and the latter two combined). The PE/filler composites were mixed by dry blending or melt compounding, moulded and mechanically tested in tensile, flexural and Charpy impact mode. The aim of doubling the tensile modulus of rotomoulding grade PE was achieved by the melt compounded, rotomoulded PE/fly-ash composites. The introduction of maleic anhydride grafted linear low density polyethylene (MA-g-LLDPE) coupling agent also increased the modulus and tensile yield stress of LMDPE with the addition of fly-ash. However, the beneficial melt flow rate and impact toughness of PE decreased significantly with the addition of fly-ash. The latter was especially true for rotomoulded samples. As the RM industry typically uses finite element analysis (FEA) to numerically approximate the stress or deflection of load-bearing parts, phase 2 of this study focused upon developing numerical material properties for FEA of the new PE/fly-ash composites. Physical measurements from compression tests on rotomoulded PE/fly-ash safety steps were close to FEA approximations (confirming the practical value of the numerical materials data), except in the case of the unfilled and highest filled PE samples. The significant differences observed between physical measurements and FEA were probably due to complex factors such as the non-linear behaviour of PE and the variation in wall thickness of rotomoulded parts, highlighting the importance of properly understanding the finite element method (FEM) for RM.