This research investigates the influence of Ultra-High Temperature Ceramic (UHTC) additives on the microstructure and oxidation behavior of Ceramic Matrix Composites (CMCs) synthesized via Reactive Melt Infiltration (RMI). The study focuses on three key parameters of the UHTC additives: particle size, additive volume, and chemical composition. Comprehensive material characterization was conducted throughout the RMI process to study the relationships between these parameters and the resulting microstructural quality. The synthesized samples were subjected to furnace oxidation tests at 1000°C and 1200°C over varying exposure durations. The experimental results demonstrated the oxidation response of ZrB2- and ZrC-based UHTCMC materials produced by RMI, providing insights into optimizing additive selection and processing conditions for improved (ultra)-high temperature application.

Zirconium carbide (ZrC) is a promising ultra-high-temperature ceramic (UHTC) for thermal protection systems (TPS) due to its high melting point, thermal stability, and mechanical strength. However, its susceptibility to oxidative degradation and limited thermal shock resistance poses challenges for aerospace applications. This thesis investigates how prior oxidation history (defined by exposure temperature and duration) influences the thermal shock response of the zirconia oxide scale on monolithic ZrC. Samples were oxidized at 600°C, 700°C, and 800°C for varying durations, followed by thermal shock via water quenching. Post-exposure analysis using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and mass change measurements showed that increasing oxidation severity leads to thicker, brittle oxide scales with higher monoclinic ZrO2 content and elevated crack densities. A transition to failure-prone behavior occurs between 700°C and 800°C, with failure thresholds defined by a ≥10% surface crack density and monoclinic ZrO2 content exceeding 10%. These results establish oxidation-dependent limits for ZrC’s thermal shock resistance.

Our reliance on synthetic structural materials has contributed extensively to environmental degradation, resource depletion, and pollution. The urgent need for sustainable alternatives has sparked interest in bio-based materials that align with Nature's cycles while maintaining high performance. However, finding such alternatives has remained challenging, especially for ceramics, which typically require high-temperature processes to achieve structural integrity. Yet Nature offers a promising blueprint: the nacreous layer, "mother of pearl", found in molluscan shells. Millions of years have allowed these invertebrates to evolve remarkable defect tolerance, achieving strength, stiffness, and toughness - a combination elusive in most conventional ceramics.

Despite extensive efforts, mimicking the intricate microstructure of nacre to achieve new, advanced materials remains challenging. Recent studies have leveraged the outstanding shaping freedom and microstructural control offered by additive manufacturing to provide new opportunities. However, these approaches continue to rely on sintering to improve mechanical properties, thereby undermining their ecological potential. The underlying printing process also remains largely unexplored. This thesis confronts both challenges by exploring a novel bacterial stiffening approach in direct ink writing using various material compositions. For the first time, mineral-depositing bacteria are incorporated into a ceramic-biopolymer suspension in an attempt to achieve sinter-like stiffening of the structure at reduced energy expenditure.

Direct ink writing ceramic-polymer bioinks is challenging due to the sensitivity of colloidal dispersions to changes in electrostatic and steric interactions, further complicated by strongly time-dependent rheology. These aspects hindered exploring the effects of biomineralisation on material performance. A 'printing window' is identified, beyond which bacteria-induced coagulation disrupts extrusion, establishing an essential constraint. Printability may be improved by controlling pH, performing more appropriate rheological experiments, and tuning rheology. Nutrient and bacterial content reduced material strength, meaning that any positive effect of biomineralisation must at least overcome this negative influence to provide a net benefit. Excessively high void content highlights the need to maximise compaction and solid content. Crucially, biomineralisation was achieved in preliminary tests, suggesting that the approach is fundamentally promising. These findings provide critical insights and guidelines for developing shaped, strong, tough, and sustainable ceramic materials, paving the way towards eco-friendly materials inspired and built by Nature.

Poor recyclability and high carbon footprint have presented a major hurdle to the adoption of thermoset composites . Natural fibre composites offer a reduced CO2 route to reinforcing fibres whilst recyclable epoxy chemistries might lead to reinforcement recovery at end-of-life. Here, short bamboo fiber reinforced epoxy composites are manufactured and recycled to achieve resusable resin and fibers. Structure property characterisation before and after recycling reveal fibre preservation whilst more than 80% of the resin can be recovered and used in the form of a low property thermoplastic epoxy. Overall, this thesis contributes a step towards development of truly sustainable and recyclable composites.

Additive manufacturing technologies are widely gaining more attention, resulting in the development or modification of 3D-printing techniques and materials. At the same time, economical and ecological aspects force the industry to develop materials that are easier and quicker to manufacture, while attaining their desired properties. The electrochemistry field can certainly take advantage of this fabrication tool for sensing and energy-related processes. In particular, the fabrication of flexible sensing devices could extensively benefit from the currently developed 3D-printing techniques, such as fused-deposition modelling (FDM) and stereolithography (SLA), as they provide a good platform for the integration of flexible materials (polymers). Mechanical flexibility of the electrodes is desirable for biomedical sensing applications, as it improves contact between sensor and skin or neural tissue by adopting the shape and decreases mechanical stress.

Boron-doped diamond (BDD) is a popular material for electrodes because it exhibits metal-like conductivity when sufficiently doped with boron atoms. BDD possesses highly desired electrochemical characteristics such as wide potential window and low background current, while attaining diamond’s chemical stability and biocompatibility. The hardness of diamond, however, has hindered its applications in flexible electrodes due to the mechanical property mismatch between diamond and flexible substrates. Moreover, common manufacturing techniques that focus on flexible BDD electrodes are time-consuming and require complex material transferring steps.

In this work, two 3-D printing techniques, FDM and SLA, have been employed to explore the possibility to prepare 3D-printed flexible BDD-based electrodes. The effect of selected 3D printing technique, particle concentration, treatment process on the mechanical, morphological, electrical and electrochemical properties of the developed composites was thoroughly investigated. A common feature for both SLA and FDM fabrication processes, the presence of BDD particles in the polymer composites resulted in enhanced mechanical properties such as Young’s modulus (increased by 230% and 75%, for FDM and SLA, respectively), but caused a reduction in tensile strength and elongation at break. The FDM-based composites additionally allowed higher weight percent of BDD fillers to be introduced, 40 wt.% in contrast to only 12.5 wt.% achieved by SLA. For this reason, further development of composite electrodes was devoted to FDM, which allowed higher weight percentage of fillers to be introduced in the polymer.

Herein, we report, an innovative, flexible, 3D-printed conductive composite was developed through FDM that displayed promising mechanical and electrochemical characteristics. By using a unique combination of a flexible polymer, thermoplastic polyurethane (TPU), and fillers, BDD particles and carbon nanotubes (CNTs), a conductive composite material was fabricated which enabled its use as a flexible electrode. Three different compositions were fabricated that each consisted of TPU, CNTs and BDD, with CNT-to-BDD ratios of 1:0, 1:1, and 1:2. For the TPU/CNT/BDD electrodes, the electrical conductivity was significantly improved with the addition of BDD particles and displayed an increase of over 7 times (up to 1.2 S/m) compared to without BDD. This effect was similarly visible in the electrochemical characterization, and well-developed peaks were observed in the presence of two commonly used redox markers [Fe(CN)6]3−/4− and [Ru(NH3)6]3+/2+ with increasing BDD concentration. Surface treatment of the TPU/CNT/BDD electrodes drastically enhanced electrochemical properties such as double-layer capacitance (Cdl) by 250 times, but also reported significant increase in peak current intensities for both redox markers. A prominent drop in peak-to-peak separation (∆EP) for [Ru(NH3)6]3+/2+] redox marker was noticed when the electrodes were incorporated with BDD particles. From 178 mV for TPU/CNT, it decreased to 110 mV for the highest BDD-loaded electrode (TPU/CNT/BDD(1:2)). The detection of dopamine was successfully achieved through the fabricated BDD-based composite electrodes. This study provides a state-of-the art, novel composite material that is characterized by excellent flexibility, attractive electrical conductivity and promising electrochemical characteristics. It provides insights into the interactions between composite components and their impact on the electrical and electrochemical properties of the 3D-printed surfaces.

In the past two decades, there has been a substantial increase in the use of natural fibres in bio-composites; these fibres have a Greenhouse gas (GHG) footprint of about 60,000 times less than virgin carbon fibres. The synthesis of polymers from renewable resources is gaining importance as a solution to the critical issues of depleting crude oil reserves and widespread pollution. To date, polymers have been manufactured utilising a vast array of biomass and bio-based platform chemicals. One such polymer is Polyurethaneane. Polyurethane (PU) is typically produced through the reaction of a polyol (polyol polyether or polyol polyester) derived from petroleum with isocyanate. With a few adjustments to the polyols and diisocyanates, the properties of PU can be significantly improved. Due to its adaptability, PU is utilised in many products, such as foam, spandex, coatings, and adhesives. Despite its usefulness, the primary raw material of Polyurethaneane (PU) is petroleum-based material which is nonrenewable and has low biodegradability, resulting in severe environmental problems. Cellulose, vegetable oil, lignin, proteins and starches are all biological components that can be used in the synthesis of Polyurethaneane (PU). These biomass materials are advantageous because they are abundant, inexpensive, high-yielding, and have a minimal environmental impact. The primary focus of this study is new developments in synthesising polyols from biomass and their use in PU materials. The primary goal of this research is to characterise a PU produced from algae biomass and utilise this to manufacture a prototype composite material. Whilst also studying the amount of carbon dioxide embodied in the system. The thesis aims to conclude that bio-based resin systems can produce good mechanical properties while reducing environmental impact.