Rotational moulding is a low pressure, high temperature manufacturing method and is considered to be the best for making large hollow shape plastic parts. Due to its long heating cycle, mould rotation during heating and slow cooling rate, it is completely different from injection or other moulding processes. The mechanical properties of rotationally moulded plastics are totally dependent on unique heating or cooling cycles. With the growing demand for rotationally moulded plastics in load bearing and other applications, a better understanding of their fracture properties is essential. In the rotational moulding process, multilayer plastic products such as skin-foam-skin three layered sandwich structures can be manufactured in a single manufacturing step without any joints. It exhibits relatively high stiffness, strength-to-weight ratios and is used increasingly in various applications such as automotive and marine. During the lifetime of the sandwich material, it may face multiple or repeated impact events. Therefore, the aim of this work is to develop a better understanding of the fracture behaviour of rotationally moulded plastics in order to use them in skin-foam-skin sandwich structure and reduce in-service failures due to impact. Here, rotationally moulded two different commercially available Polyethylene (PE) and Polypropylene (PP) plastics are tested. Microstructural details of the plastics are investigated here. Fracture properties, particularly fracture toughness properties are studied using J-integral elastic-plastic fracture mechanics approach to identify the fracture initiation point. Impact properties are also investigated at a wide range of temperatures. PE materials are found to have better fracture properties. It is observed that with the fracture toughness plastic’s microstructure particularly crystal and amorphous region thickness are related. The understanding from these works is followed by the manufacture of rotationally moulded skin-foam–skin sandwich structure and testing of low velocity impact properties of this structure from 20 J to 100 J energy level with a drop weight impact testing machine. PE is used for both in skin and core layer and sandwich samples are manufactured at four different skin-core thickness combinations. Impact force resistance and bending stiffness are found to be increased with an increase of both skin and core layer thickness. Low velocity repeated impact properties of the rotationally moulded sandwich samples are also investigated from 20 J to 50 J energy level at the end of this project to understand the effect of repeated impact on the sandwich structure. The samples are subjected to single impact event repeatedly up-to penetration at each energy level. Impact energy-impact number curve obtained from repeated impact test provides an equation for prediction of the number of repeated impacts for the penetration of the sandwich samples at each energy level.

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This study aimed to develop methods to improve PHA production from selected volatile fatty acids (VFAs) and to improve the understanding of the PHA production process by pure culture bacterial fermentation using Cupriavidus necator. Optimisation strategies involved the following investigations using shake flasks and 5 litre based batch fermentations: Shake flask investigations determined that the temperature of 30oC and a nutrient medium, resulted in the highest growth of bacteria. A feeding strategy of the substrate (VFAs - acetic acid and butyric acid) was developed to avoid inhibition by the substrate and the alkaline buffer. The results established that continuous feeding of VFAs based on maintaining optimum pH around 7 resulted in enhanced PHA yields by almost 2-fold when compared to single pulse feeding of acetic and butyric acids (at 1, 2, 3, 4 and 5 g/l VFA concentration). A novel application of a capacitance probe was demonstrated to be able to monitor maximum PHA accumulation in-situ and in real-time, so as to prevent product and substrate loss (acetic and butyric acids, by a maximum value of 12 g/l and 20 g/l respectively), and to increase PHA process understanding and fermentation kinetics. The dielectric spectroscopy probe was able to correlate very well (R2 = 0.862) with PHA off-line measurements when operated in dual frequency mode and was able to establish the optimum PHA harvesting time, which would have resulted in improved process economics and environmental performance. Shake flask experiments were conducted to investigate the addition of trace metals (zinc, manganese, boric acid, cobalt, nickel and sodium molybdate), copper and sodium chloride in nutrient media and its effects on bacteria growth. NaCl contributed to the greatest enhancement in the early growth of bacteria and therefore fed batch fermentations using 0, 3.5, 6.5, 9, 12 and 15 g/l of additional NaCl concentrations were evaluated. The 9 g/l NaCl concentration showed the highest PHA production of 5.33 g/l and also caused PHA accumulation to occur earlier by 2 h than the control. The capacitance probe also helped visualise and understand the bacterial growth and PHA accumulation profile. The novel use of low cost digestates based media was demonstrated. Results demonstrated that possibly due to the nutrients/trace elements in a digestate (from food wastes and wheat feed) the PHA accumulation was enhanced by 3-fold (to 12.29 g/l); with a resulting highest ever reported PHA accumulation of 90% for C. necator. C: N: K: P: S ratios for this digestate based fermentation were found to be for growth 761: 31: 1: 3.5: 1.9 and for PHA accumulation 1132: 11: 3: 1.7: 1. Digestates use within biotechnology and biorefining specifically for bacterial applications could provide another alternative route to digestate disposal that may lead to valuable end products. All the above evaluations represented novelty and have delivered significant process optimisation for PHA production from VFAs.

In common with all composite materials, Aromatic Polymer Composite-2 (APC-2) is inherently expensive and as such any reclaimed material is potentially extremely valuable. In this work, pieces varying from 6.35-25.^mm square (0.25-1.Oinch) were cut from APC-2 single ply prepreg of thickness 0.125mm and compression moulded into panels 150mm square, with the thickness controlled to meet the requirements of subsequent characterisation. Further work was carried out on panels of the same dimensions moulded from squares cut from 8 ply preconsolidated APC-2, the size of these squares ranging from IQ- 25. 4mm square. The flexural, tensile and compressive mechanical properties, fracture and impact toughness, and creep behaviour of these composites were determined, as a function of particle size. Finally, the potential for moulding was assessed. Results from tensile and flexural tests show that the variations in the tensile and flexural moduli of the composites increase linearly with particle size. Using suitable modifications of planar reinforcement theory to produce a quasi-isotropic theory, an accurate prediction of the experimental values is possible, from the Modulus Reduction Factor [MRF]. A similar approach with respect to the experimental strength can only be made if the mode of failure is known. The fracture toughness of the composite moulded from single ply prepreg was found to be greater than that of continuous fibre reinforced APC-2 and increased with decreasing particle size over the size range examined. Fractographic analysis of this phenomenon revealed several toughening mechanisms: Polyetheretherketone (PEEK) rich zones act as crack arresters; fibre bundle and particle bridging of the crack increase the work to fracture. Impact toughness is greatly enhanced over injection moulded composites for similar reasons. The creep property profile is very promising and shows retention of the creep resistance of PEEK and carbon fibre. The formability shows a possible opportunity for component manufacture otherwise impossible at present.

This thesis attempts to trace the history of pvc from the first synthesis of the monomer in 1835 to the stage of its development at the outbreak of the Second World War. It deals with the theoretical and industrial aspects of the chemistry involved in the manufacture of the monomer, polymer and its modifications and with the major aspects of compounding pvc, It also discusses the evolution of the machines used to process the plastic from those which were used in the rubber industry. The final chapter considers some of the early applications of pvc and the factors which stimulated its widespread use.

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Laser sintering (LS) is an additive manufacturing technique that allows production of prototypes and fully functional components characterised by the highest level of freedom of design currently achievable. High customisation, multi-functional integration, design optimisation and the potential for reducing cost and production time of a single item are the most outstanding characteristics of the LS process. However, the small number of polymers at present available constitutes a significant drawback for many engineering applications, especially in the automotive and aerospace industrial sectors where seemingly only one commercial high temperature grade, Poly Ether Ketone (PEK) HP3, can meet the high material performance required. With the aim to expand the choice of materials for LS and especially High Temperature Laser Sintering (HT-LS) manufacturing, this research project has focused on the investigation and implementation into LS of a new high temperature polymer, Poly Ether Ether Ketone (PEEK). This study has examined some of the key requirements needed for the successful development of new materials in LS processes at experimental and theoretical levels. Two generic PEEK grades 150PF and 450PF have been quantitatively investigated in parallel with well-established LS polymers in terms of particle size, particle morphology and flow behaviour. A calculation of the inter-particle interactions has been evaluated for all the materials proposed. These analyses, coupled with two strategies for the improvement of powder flowability, have formed a systematic and fundamental approach for studying powders in LS. The PEEK 450PF grade has been selected for optimisation into the HT-LS system, EOSINT P 800. The HT-LS processing parameters and their effect on the mechanical characteristics of the laser sintered units have been investigated and optimised, and new insights into the HT-LS mechanisms and functionalities of the EOSINT P 800 system are presented. A basic technique for the prediction of one of the HT-LS processing temperatures is proposed. A formula for linking material properties to processing parameters has also been assessed. Lastly, the medical equivalent grade of PEEK 450PF, PEEK-OPTIMA® LT1, has been utilised for the manufacture and test of two medical components.

A series of biodegradable star poly(ε-caprolactone) (PCL)-based polyols and PCL-based diisocyanate prepolymers were synthesised and fully characterised. Biodegradable polyurethanes (PUs) were synthesised using star PCL-based polyols and either biodegradable diisocyanate prepolymers 4,4’-methylenebis(phenyl isocyanate) (MDI) or 2,4-toluene diisocyanate (TDI). The resulting polyols, diisocyanate prepolymers and PUs were subjected to enzymatic degradation using lipase for up to 30 days. Chapter 1 is a general introduction to the reactions involved in the syntheses of PU foams and the ring-opening polymerisation of cyclic esters. The general components used in PU formulations including biodegradable polyols and diisocyanate prepolymers are discussed. Furthermore, polymer biodegradation testing methods and analytical methods to monitor degradation are investigated. Chapter 2 includes the syntheses and enzymatic degradation of a series of biodegradable four- and six-arm star PCL polyols. This was achieved through the tin(II)octoate (SnOct2) catalysed ring opening polymerisation (ROP) reaction of ε-caprolactone (ε-CL) using pentaerythritol, di(trimethylolpropane) and dipentaerythritol initiators. Furthermore, a series of six-arm star poly[(ε-caprolactone)-co-(β-butyrolactone)] were synthesised in a similar manner. Star PCL and star poly[(ε-CL)-co-(β-BL)] both exhibited almost 100% mass loss after 15 days of enzymatic degradation at a constant rate. Generally, an initial increase in % crystallinity (%χc) is seen for star PCL and star poly(ε-CL)-co-(β-BL) in the first few days (0-3 days) of enzymatic degradation. This was followed by a decrease in crystallinity (%χc), indicating amorphous regions of the polymer were preferentially degraded. This was supported by scanning electron microscopy (SEM) analyses showing surface pitting and occurrence of crystal spherulite structures within the first few days of enzymatic degradation. Chapter 3 concerns the synthesis and enzymatic degradation of a series novel four-arm dumbbell-shaped copolymers (PCL)2-(PEG)-(PCL)2 bridged with 2,2’-bis(hydroxymethyl)propionic acid (bisMPA) moieties. This was achieved by the synthesis of a tetra-hydroxyl PEG macro-initiator through a coupling reaction of poly(ethylene glycol) (PEG) and acetyl-protected bisMPA using dicyclocarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP). Subsequently, the four-arm star structure was synthesised with the SnOct2 catalysed ROP of ε-CL using tetra-hydroxyl PEG macroinitiator. Contact angle and %water uptake (%WU) indicated the copolymers containing a higher %PEG showed increased hydrophilic nature and surface wetting. A dispersity (Ð) of 1.32-1.51 and a small molecular weight shoulder were seen due to using a polydisperse PEG macro-initiator and the high viscosity of the reaction mixture under bulk conditions. The novel star copolymers showed >90% mass loss within 7 days and an increase in %χc within the first few days of enzymatic degradation. Chapter 4 entails the synthesis and enzymatic degradation of biodegradable seven arm star PCL with a central acetylated β-cyclodextrin (β-CD) moiety. This was achieved through a four step synthetic route involving the protection of 1° OH groups on the β-CD moiety, acetylation of the 2° OH groups on the β-CD moiety, removal of protecting group on the 1° OH group and subsequent ROP of ε-CL catalysed by SnOct2. Contact angle and %WU analyses showed minimal surface wetting and high hydrophobicity. A very low rate of enzymatic degradation was seen with 7% mass loss and a general increase in %χc in 20 days. Chapter 5 involves the synthesis and enzymatic degradation of a series of biodegradable diisocyanate prepolymers containing a central PCL or PCL-b-PEG-b-PCL moiety and capped with either MDI or TDI moieties. This was achieved through the reaction of two molar equivalents of the diisocyanate moiety, MDI or TDI, and either PCL diol or PCL-PEG-PCL triblock copolymer. The diisocyanate prepolymers showed absorbances attributing to the C=N stretch in the NCO group as well as N-H and C-N in the urethane group in FT-IR spectra. Contact angle and %WU measurements of diisocyanate prepolymers with higher %PEG showed increased surface wetting and hydrophilicity. Generally the TDI-based diisocyanate prepolymer showing 100% mass loss in 4 days, degraded at a faster rate than MDI-based diisocyanate prepolymer of 23% in 40 days. Furthermore, the lower Mn MDI-based prepolymer showed a significantly faster rate of enzymatic degradation of 79% mass loss in 40 days than the higher Mn MDI-based prepolymer. Chapter 6 concerns the synthesis and enzymatic degradation of a series of biodegradable PUs using biodegradable PCL-based star polyols and diisocyanate prepolymer components synthesised in Chapter 2-5. PU gels were produced as a result of a minimal amount of dichloromethane (DCM) solvent to ensure complete mixing. Generally, PUs showed the disappearance of the C=N stretch in fourier transform infrared spectroscopy (FT-IR) analyses, indicating all NCO groups successfully reacted to give urethane groups. PUs showed up to 18.5% mass loss over the 30 days of enzymatic degradation. Comparisons of the PU degradation behaviour were made to demonstrate the effects of polyol type, diisocyanate type, and ratio of NCO:OH used, on the rate of PU enzymatic degradation. Chapter 7 surmises and concludes the work covered in Chapter 2-6 and suggests further work.

Management of plastic wastes is a primary environmental concern and recycling has become unavoidable. A novel approach to plastics recycling is feedstock recycling with which the plastic waste is decomposed in a controlled manner to provide useful chemicals, with liquid fuels as the main target. Hydrocracking arises amongst feedstock recycling alternatives with some advantages such as being an exothermic reaction (energy being a useful by-product) and providing a high quality fuel. Hydrocracking of plastic wastes has focused some attention on researchers worldwide. Model compounds, virgin plastics and plastic wastes have been hydrocracked. Batch autoclave reactors were, virtually, the only system used for these tests. In the literature, a range of catalysts were essayed and typical conditions of reaction were: hydrogen pressures of 70 bar, temperatures of 400°C and reaction times of 60 minutes. Total conversions of polymers such as HDPE were obtained with oil yields reaching 70 %. However, reported researches present some important gaps such as: poor analysis of products of reaction, poor definition of targeted product, limited study of reaction parameters, very little catalyst development or study, no deactivation assessments and no heat balance or thermodynamic analysis. This research tries to address most of these understudied issues. A batch autoclave reactor with an in-house developed sampling system was used to perform hydrocacking tests. The main catalyst group targeted was platinum loaded zeolites which have been overlooked in the literature despite their potential as being highly active and selective. A series of USY and one MOR zeolites (in sodium form) were ion exchanged with Pt(NH3)4Clzsalt to obtain 1% and 0.5% Pt loadings. Then were dried, calcined and activated by slow heating under hydrogen atmosphere obtaining the H form of the zeolite with the metal in its 0 oxidation state.