Large-scale additive manufacturing for high-temperature polymer composites presents challenges in printability and the microstructure, limiting its overall application. To address this, a series of experiments were conducted to analyse the effects of various printing parameters, which are material number, printing dimensions, volumetric output, and heating zone temperatures. Additionally, the impact of nozzle pressure and design modifications, such as nozzle insulation, was evaluated.
The results indicate that nozzle insulation significantly affects the required torque and void content of semi-crystalline polymer composites. However, heating zone 1 was identified as a limiting factor for high-temperature amorphous polymer composites, as its heating band did not provide sufficient heat to the barrel.
These findings highlight the importance of optimizing printing parameters and extruder design to expand the applicability of high-temperature polymer composite printing, for example, a greater range of volumetric outputs. It is recommended that additional pressure and temperature sensors be installed between different screw regions for better insight into extrusion behaviour. Additionally, a nozzle design for viscosity measurement is proposed to better investigate the influence of temperature and volume output on the viscosity.

This research focuses on modeling the thermal expansion behavior of high-end 3D printed fiber-reinforced polymer composites during autoclave cycles. Utilizing a combination of finite element analysis (FEA), analytical modeling, and experimental thermo-mechanical testing, the study aims to predict and validate the coefficient of thermal expansion (CTE) of these materials.

The investigation primarily examines the influence of fiber orientation and void content on thermal expansion properties. Experimental techniques, including optical microscopy, x-ray tomography, and dynamic mechanical analysis (DMA), were employed to assess microstructural properties and thermal behavior. Results indicate that the use of a breaker plate during extrusion enhances random fiber orientation, promoting isotropic thermal expansion.

The CTE values for aligned and random fiber orientations were analytically modeled using short fiberreinforced polymer (SFRP) models, demonstrating good alignment with experimental data trends. The study also found that void content only minimally affects CTE, contributing to a slight increase of approximately 5%.

Despite discrepancies between FEA predictions and experimental outcomes, FEA remains a valuable tool for identifying thermal expansion trends and guiding manufacturing process optimizations. Future work should refine modeling assumptions and expand experimental validation to enhance the predictive accuracy of thermal expansion behavior in large-format 3D-printed molds.

When designing mechanical components, they commonly undergo multiple modeling phases for stress determination using analytical or numerical methods like the Finite Element Method (FEM). This is followed by experimental validation performed via stress mapping to identify and account for possible mechanical failure within the design phase. Among the experimental stress mapping techniques, mechanosensing is gaining rapidly increasing attention by research and industry. Mechanosensing is a chemistry-based technique that utilizes molecules called mechanophores. When mechanophores are embedded in transparent polymers, they act as mechanical probes sensing stress/strain throughout the polymer by emitting fluorescence under deformation. While studies have shown the capabilities of mechanophores as stress/strain probes qualitatively, it is currently not known how the mechanophore activation is correlated with the stress/strain-based quantities from a solid mechanics perspective. This study addresses this problem from a phenomenological viewpoint to fill the research area gap. In this work, using a uniaxial tensile testor, experiments are conducted on a Polydimethylsiloxane (PDMS) with a mechanophore spiropyran embedded homogeneously in the bulk of the polymer. The fluorescence data captured in the tests is correlated with the numerically obtained continuum mechanics stress/strain quantities. These correlations will be useful in giving directions towards research in the fundamental understanding of the mechanics of mechanophores, thereby bridging the gap between chemistry and mechanics of mechanosensors. This will pave the way towards optical-only in-situ measurements of stress-strain behavior.

Transparent Natural Fiber Composite Materials may pose a more environmentally friendly alternative regarding energy efficiency and low CO2 emissions in contrast to traditional composites, exhibiting transparency for future smart building or photovoltaic applications. The present study involved a research effort for the development of a lightweight flax fiber-reinforced composite material, which will exemplify high optical transparency. A detailed focus is conducted, on minimizing light absorption phenomena with delignification methods of flax fibers, eliminating light scattering via a Refractive Index Matching procedure between the reinforcement and the polymer matrix and via fiber modifications which tackle several issues such as enhancing the imperfect interphase between the hydrophilic reinforcement and the hydrophobic matrix, or providing finer polymer impregnation of the fibers. Acetylation, nitric acid, or TEMPO-oxidation treatments that modify the fiber’s nature and morphology are implemented to tackle these obstacles. Transparent Flax Fiber Reinforced Composites of 35-45 % fiber volume fraction were fabricated with wet-lamination and hot press forming techniques, indicating a maximum total light transmittance of approximately 70% (at low thickness) and 56-58% (at high thickness), depending on the fiber modification implemented. Regarding mechanical properties, a maximum specific flexural strength of 153 MPa/(g/(cm3)) and a specific flexural stiffness of 11.95 GPa/(g/(cm3)) was achieved for these materials. The transparent FFCMs showed comparable values of total light transmission correlated to reference materials like GFRPs or other natural fiber-reinforced composite materials, with similar volume fractions, signifying the success of achieving high optical transparency.

Continuous casting is the dominant manufacturing method of steels, accounting for over 90% of global steel production. Mould slags, which are calcium silicate glasses, play a crucial role in this process due to their multifunctional purpose, directly impacting the safety, quality, and efficiency of steel production. As the steel industry transitions toward greener practices, new challenges arise, including the need for fluorine-free mould slags to meet increasingly stringent safety and environmental regulations. Historically, mould powder development has relied heavily on trial-and-error approaches, limiting the development rate of these materials for new demands. This thesis is part of a broader research effort aimed at understanding the structural transformations that drive the desired material properties of mould slags. In this study, various characterization techniques—such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-temperature Raman spectroscopy (RS)—were employed to investigate the structure of an industrial mould slag, with a focus on its heat transfer properties. Samples were melted and then solidified followed by three different isothermal holding temperatures to replicate the thermal cycling experienced during casting. The multi-method characterization revealed that the industrial mould slag (S1) consists of three distinct phases: cuspidine, combeite, and a glassy matrix. These phases were present regardless of the isothermal holding temperature. The microstructure after solidification featured large faceted cuspidine crystals embedded within a mixture of smaller dendritic combeite crystals and the glassy phase. High-temperature RS measurements showed that the formation kinetics of the S1 mould slag were faster than anticipated based on previous research. This highlights the necessity of multi-method characterization, and not to rely only on the chemical composition to fully understand mould slags and adapt them to future industry requirements. While there is room for improving the accuracy of the utilized technique, high temperature RS measurements have demonstrated their value in mould slag research and, with further refinement, hold the potential to unlock new research opportunities.

Plastics are a common material used in everyday life due to their desirable mechanical properties and affordability. However, their utilization pose challenges at the end of their lifecycle, leading to environmental pollution. Therefore the valorization of waste plastics is very important. In order to address this, we propose a mechanochemical approach to activate inert polymers found in common plastics, transforming them into reactive polymers suitable for high-value product synthesis. With the use of ball mill grinding, common polymers such as PMMA and PS underwent chain scission and their molecular weight distribution and functional groups were analyzed. Segmentation of polymers asymptotically
reach a minimum molecular weight and dispersity. The chain scission of these polymers can form radicals which rapidly undergo reactions to form new groups such as alkenes. In the presence of radical scavengers, these polymeric radicals are terminated towards RAFT capable polymers. PMMA and PS are successfully terminated with trithiocarbonate and dithiobenzoate groups, followed by repolymerization and copolymerization with respective monomers and comonomers into regenerated polymers or block copolymers. Several factors affect the effective termination of the polymers toward RAFT capable polymers, warranting further optimization. The method explored in this work offers an avenue for the complete recycling and upcycling of waste plastics into high value products, which can be a technologically feasible method to tackle the global problem of plastic waste.

Over the last 15 years or so, research has revealed the great self-healing prospects possessed by asphaltic mixtures. Researchers have proposed novel methods to harness this capability, aiming to prolong the service life of asphalt pavement, particularly in porous asphalt. To date, the most promising of the healing methods is the combined capsule-induction system. This thesis aims to ascertain whether such a system would show positive results in stone mastic asphalt (SMA). Following that, an optimisation of the composition of self-healing SMA was proposed by assessing the mechanical and healing properties via laboratory testing. Finally, an evaluation of sustainability from an environmental perspective was done using Life Cycle Analysis (LCA) methodology.

Results of the healing assessment revealed that each combined healing system was able to recover between 58-63\% of its original fracture strength after 8 healing cycles, while the reference mix (without healing) was only able to regain 10\% fracture strength before failure after 2 cycles.

Inclusion of the combined healing system slightly reduced the strength, stiffness and water sensitivity of the SMA mixture compared to the reference. However, improved rutting resistance was observed in each self-healing case. Within the self-healing mixtures, increasing capsule content reduced asphalt density, stiffness and strength and resulted in an increase in asphalt void content.

The LCA results show that the self-healing system had environmental benefits in some facets such as a 14\% reduction in fossil fuel resource depletion and a 21\% reduction in land use. However, the present total known environmental costs of other impacts are approximately 15\% lower in the reference system based on a cradle to gate, and use phase analysis. Almost half of this total cost was attributed to maintenance activities. It was concluded that a 32\% increase in maintenance efficiency would ensure environmental viability of a self-healing mixture over a reference mixture within the constraints of the analysis conducted.