Search

Self-healing materials have the ability to repeatedly repair damages that occur before complete failure of materials. The development of stimuli-responsive self-healing materials has been in demand recently for composite structures, since their failure is relatively uncertain and can result in major expenses. Using such materials can enhance damage tolerance, leading to greater asset reliability - it also limits expenditure and keeps the need for human interventions to a minimum. This work investigates Fe3O4 magnetic polymer nanocomposites that can be used to intrinsically heal composites through thermal stimuli, followed by self-healing of glass fibre reinforced polymer (GFRP) composites, which are fabricated by embedding the healable polymer nanocomposite as one of the sacrificial layered matrices. However, performance of nanocomposites depends on various parameters, including nanoscale dispersion of nanoparticles. Specifically, a lack of hierarchical dispersion of nanoparticles in three-dimensional polymer matrices prevents electron tunnelling and deteriorates the nanocomposites' ability to conduct heat stimuli or otherwise lead to pyrolysis. To address this issue, two functionalisation techniques - viz. silica (Stöber method for lower silica loading and tri-phasic reverse emulsion method for higher silica loading), and oleic acid (22%, 33%, 44%, and 55% w/w of nanoparticles) variations - were experimentally investigated as capable of changing hydrophobic characteristics for facilitating uniform dispersion of the Fe3O4 magnetic nanoparticles (MNPs). The main focus of the presented work is to understand the role of functionalisation routes in the particle-polymer interface in forming a uniformly dispersed and hierarchical network of MNPs in a polymer matrix. Emphasis was on understanding and optimising the role of activator and initiator proportions in controlling the in-situ polymerisation of PA6, capturing the MNPs dispersion state. The resulting dispersion state due to functionalised Fe3O4 MNPs determined the properties of magnetic PA6 nanocomposites (PMC) to help achieve a generic set of principles for designing the desired materials for stimuli-induced self-healing of GFRP composites. The method used to achieve this involved firstly undertaking anionic ring-opening in-situ polymerisation of PMC by experimental synthesis within the laboratory, with optimised EtMgBr (activator) and NACL (initiator) proportions for improved degree of crystallinity, and capturing the MNPs dispersion state attained by probe ultrasonication of the melt monomer & MNPs solution mixture. Based on this, 50% EtMgBr (activator) and 30% NACL (initiator) were assessed as the optimised proportions for giving the highest possible crystallinity amongst all the prepared PMC variations. Secondly, as per the functionalisation type of the MNPs, the prepared PMC samples were tested based on chemical, thermal, structural and magnetic characterisations, for the purpose of assessing their self-healing capability by microwave stimuli. The physical characterisation results were also used to train a simulation model to create the 3D dispersion state, for better studying the dispersion state and interaction region defined by the interaction radius (IR) of each MNP/agglomerate of the MNPs. Based on this overall comparison, the most suitable PMC of 22 w/w % OA loading was selected and formed into thin films. Sandwiched tensile testing samples were then prepared using this PMC film as a sacrificial layer between GFRP tapes. Both bare and modified Fe3O4 MNPs PMC exhibited paramagnetic behaviour, with average particle sizes ranging from 30-60 nm. The saturation magnetisation (Ms) of the unmodified MNPs PMC was around 65% and that of the selected PMC with 22 wt/wt % OA loading was 47%. The self-healing concept was demonstrated with the prepared composite samples' microwave induction heating, and the efficiencies based on strength recovery were calculated as 84%, 58% and 34% after first, second and third healing, respectively. This can essentially increase the life-cycle viability of the composite structure by over 175% (with 60% certainty) compared with that of an otherwise damaged structure, hence promising cost saving by extending the structural life.

Unconventional oil and gas operators are currently facing the challenge of casing lateral buckling and/or deformation during shale gas wells stimulation through hydraulic fracturing. Failure of the casing during this process can lead to huge financial loss, catastrophic consequences and even fatalities depending on the magnitude and circumstance of the incident. An in-depth literature review was conducted, focusing on casing lateral buckling /deformation, factors attributing to casing failure, failure mechanism, and the resulting failure mode in shale gas horizontal wells. The study covered casing types, failure modes and mechanism, and impact of material selection on casing failure, with the viewpoint of casing failure mechanism, cement and rock as an integrated system. In the follow up, the casing material selections were investigated using ANSYS Granta Edupack (CES) and multicriteria decision making (MCDM) for three different scenarios of buckling tendencies. A finite element analysis (FEA) was then undertaken, using two simulation scenarios for casing structural integrity in both radial and axial configurations under the mechanics of a combine system - casing, cement and formation rock. There was then a detailed novel study on casing structural integrity using both FEA and machine learning. This research revealed the effect of combined loading, using multiple parameters to establish the relationship and effect of each on stress, displacement and ultimately casing safety factor. Finally, real-time parametric prediction and optimisation using Lunar and Quasar (ODYSSEE software package) enabled the examination of the casing structural responses based on the pertinent parameters. A similar trend was found between "KNN" and Lunar predictions in terms of how parameters influenced casing buckling phenomena and the corresponding Mises stress. In conclusion, the FEA study showed that time-dependent rock slippage-creep during stimulation lead to an increase transverse displacement and corresponding stresses on the casing. This new understanding is a major breakthrough in establishing casing health status during shale gas well stimulation. The optimised design shows 89% reduction in total deformation and 87% reduction in von Mises, in comparison to unoptimised simulation result. Also, the optimised design gives a safety factor of 3.3 against the previous 0.8129 without optimisation. The Lunar optimisation provided the ideal parameter values for the attainment of pre-defined von Mises stress as a function of other factors during the design phase. This quick approach shows both accuracy and validity, since the two independent procedures arrived at the same conclusion. We found that concurrent investigation of the attributing factors to casing buckling, alongside optimisation using FEA and the ODYSSEE package, was sufficient to maintain casing structural integrity during the shale gas extraction process. The study also revealed alternative and better suited materials choices than those that are currently preferred commercially (P110 and Q125).

Oil-based mud (OBM) wastes are generated every year all over the world, and remain a serious challenge for the oil and gas industry. The potential solution for this global problem is either to destroy these hazardous chemicals completely - a significant challenge - or to use/utilise them for beneficial applications. Therefore, the aim of this thesis is to develop a detailed understanding of the synergistic effects of different clay minerals that exist in OBM waste, in influencing structural, morphological, rheological and thermo-mechanical behaviour of LDPE and PA6 nanocomposite materials. The thesis begins with a critical literature review, covering oil-based mud (OBM) waste treatments, polymer nanocomposites and their manufacturing, thermal degradation behaviour and mechanical performance. This is followed by a detailed characterisation of OBM waste to determine elemental composition, and structural and thermal properties. To evaluate their performance as a filler in polymer composites, both mechanical and thermal properties of polyamide 6 (PA6) and low-density polyethylene (LDPE)-based nanocomposites were manufactured through the process of melt compounding, followed by injection and compression moulding, with different amounts (wt%) of OBM fillers (OBMFs). The study on thermal degradation of LDPE/OBM slurry shows that the nanocomposites with higher percentage filler contents (in case of 7.5 and 10 wt%) decreased the heat capacity value by 33% and 17% in LDPE respectively. OBM slurry shows superior improvements in storage modulus, loss modulus and damping property (tan d) in LDPE matrix, compared to those of LDPE/MMT nanocomposites. However, the study shows a decrease of tensile and flexural properties for the LDPE/OBM slurry nanocomposites. The follow-up study focused on thermally-treated OBM waste in powder form and their effect on thermo-mechanical properties of LDPE matrix. It was observed that OBMFs was compatible with LDPE matrix, which led to a strong interfacial interaction between the clay layers and polymer. Further, the clay minerals present in OBMFs formed chemical bonds in microstructure within the nanocomposites. The OBMFs (10wt %)/LDPE nanocomposite produced the highest onset degradation temperature at 5 wt% loss (TD5%) and 50 wt% loss (TD50%) among the nanocomposites. An enhancement of mechanical properties of composites was identified, which showed a gain of 14% Young's modulus and 18% increase on tensile strength at 10 wt% OBMFs loading, compared to those properties of neat LDPE. The crystallinity and thermal degradation behaviours of polyamide 6/oil-based mud fillers (PA6/OBMFs) nanocomposites were also investigated. TGA indicates the onset decomposition temperature of D1/2 (half-decomposition) for PA6 with 10 wt% of OBMFs is 16oC higher than that of PA6 and also registered a 47% specific heat capacity reduction. The Youngs' moduli were increased by 42% and 35% in PA6 with 7.5 and 10 wt% OBMFs nanocomposites respectively, whereas the tensile strengths were increased by 24% and 16% in PA6 with 7.5 and 10 wt% OBMFs nanocomposites respectively. The flexural strength increased by 26% with the addition of OBMFs from 0 to 10 wt% in PA6 nanocomposites. In conclusion, a loading amount of 10 wt% OBMFs on both polymer matrices was found to be the most desirable enhanced mechanical and thermal stability properties. However, 10 wt% OBMFs showed increased storage modulus and drop in loss modulus in both LDPE and PA6 matrices, leading to the conclusion that OBMFs improves thermo-mechanical properties in LDPE and PA6 matrices in dynamic condition. Considering the findings from this study, this material shows high potential for low-cost structural insulation materials as an alternative to conventional (more expensive) materials. All the proposed treatment techniques presented in the literature and in industrial practices dealing with OBM waste, passes pollution from one stage to another. This study explores the opportunity to utilise the useful reclaimed clay minerals from OBM waste as filler in nanocomposite manufacturing.

Polymer nanocomposites are becoming established widely across the industry due to (among other reasons) their lightweight performance advantages, and ability to meticulously target material properties with great control and precision. Despite the beneficial properties, certain nanofillers have shown potential health risks and toxicity, to both humans and the environment. The use and introduction of these materials into the workplace may therefore be hazardous if it involves human exposure. Research has yet to evaluate or quantify either the risk, the process of potential exposure, or the impact of embedded nanoparticles in commercial composites when they are released during machining processes. In this thesis, four groups of nanocomposites are identified as being used within industry and having potentially-harmful nanoparticles - the nanocomposites incorporate seven different nanoparticles of relevance, at different weight concentrations. This study involved the manufacture of the materials and an investigation into their effect on mechanical properties, through various methods: tensile tests, three-point bend flexural tests, SEM, EDX and FT-IR. The study employed a process approach for the assessment of nanoparticle emissions, using an automated drilling methodology in which the background noise was eliminated from the measurements. The investigation used real-time measurements with a combination of a condensation particle counter (CPC), a scanning mobility particle sizer spectrometer (SMPS), a real-time fast-mobility particle spectrometer (DMSSO) and post-test analytical methods. The research investigated the influence of a variety of nanofillers on nanoparticle release during drilling, from three different polymers: polyester (PE), polypropylene (PP) and epoxy (EP). Suitable fillers were tested for each polymer and demonstrated modifications to the material properties. The four sets of nanocomposites included PP-based, PE-based, EP-based and a hybrid EP/carbon fibre-based (EP/CF). PP-based samples were reinforced with talcum (Talc), montmorillonite (MMT) and wollastonite (WO). PE-based samples were reinforced with two weight concentrations of nano-silica (Si02) and nanoalumina (Al203). EP-based samples were reinforced with carbon nanotubes (CNT) and carbon nanofibres (CNF). EP/CF-based samples were reinforced with three weight concentrations of graphene oxide (GO). The fillers utilised within the PP-based samples were observed to decrease the material density, without significantly affecting the tensile and/or flexural properties. The fillers in the PE-based samples had minimal effect on the tensile properties; however, all of the reinforcing fillers improved both the flexural modulus and flexural strength. The incorporation of CNFs and CNTs in EP displayed both positive and negative effects on the tensile and flexural properties in comparison to the EP sample. The use of GO within EP/CF demonstrated minimal effect on both the tensile and flexural properties in comparison to the sample without nanoparticle reinforcement. The study on the PP-based nanocomposites is the first such study to explore and demonstrate the nanoparticle release from WO and Talc-reinforced composites. The nano-filled samples exhibited a 33% decrease (PP/MMT) or a 30% increase (PP/WO) on average released particle number concentration in comparison to the virgin PP sample. Size distribution analysis found a substantial percentage of the particles released from the PP, PP/WO and PP/MMT samples to be between 5 nm to 20 nm, whereas the PP/Talc sample produced larger particle diameters. The results from the PE-based nanocomposites show that the nano-reinforced samples displayed an increase in nanoparticle number concentration by up to 228% compared to virgin PE. This suggests that the nanofillers adhered to the PE matrix, showing a higher released concentration of larger particles (20 nm to 100 nm). The correlation between nanoparticle weight concentration and nanoparticle release varied considerably between the Si02 and Al203 samples. In comparison to the virgin EP, the results revealed that the EP/CNF and EP/CNT samples returned statistically significant differences for all samples, and produced an increase of 93% and 211% respectively in average particle number concentration. The particle mass concentration released from EP/CNT and EP/CNF samples demonstrates that a new perspective is needed for occupational exposure assessment of CNTs and CNFs embedded within nanocomposite materials. The incorporation of GO within the EP/CF-based samples displayed a statistically significant increase in nanoparticle release at the three different weight concentrations. However, the study did not find any relationship between filler weight concentration and nanoparticle release. Also, although a statistically significant increase was observed, the independent fillers appeared to have no effect in the characterisation and particle size distribution. Overall, 83% of the investigated samples demonstrated that the introduction of nanoparticles within the material had a statistically significant influence on the average particle number concentration: 67% of the nanocomposites displayed a statistically significant increase in the particle number concentration, while 17% displayed a statistically significant decrease. The study found no clear correlation between mechanical properties and particle number concentration; however, it was revealed to be highly dependent on polymer brittleness and ductility. The results demonstrated that the incorporation of most nanofillers can have a significant influence on particle number concentration and therefore may have a detrimental effect on nanoparticle release. On several occasions during the drilling, it was observed that the concentrations emitted by some samples were so high as to surpass the limits of the CPC instrument. The evidence presented by this research contributes a substantial amount of data for the assessment of nanoparticle release from polymer nanocomposites during drilling.