Composite materials have revolutionized the world as we know it, but along the way, we have transformed that world, which is changing and suffering from global warming. This thesis explores the potential of bio-based resins for high-performance composite applications, focusing on a bio-based epoxy derived from brown algae, PHTE. The research investigates the feasibility of PHTE to replace BADGE epoxy, a bisphenol-A-based toxic and synthetic fossil-fuel-derived epoxy that comprises a major portion of aerospace composites. The study involved comprehensive material analysis and testing, including an examination of thermal, physical, and mechanical performance and a comparison of both systems. PHTE demonstrated excellent mechanical and thermal properties with high bio-based content, although its high viscosity posed challenges for traditional manual manufacturing techniques, especially composite manufacturing. The promising properties motivates to study and develop the recipe further for other high-performance applications as well apart from aerospace.

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 cold regions, the formation and accumulation of ice can cause safety hazards and impede proper operation of equipment. By example, ice accumulation on aircraft wings can increase drag, increase weight, reduce upward force and decrease aircraft speed. For these reasons, proper anti- or de-icing techniques need to be developed. These techniques can be divided in passive and active systems. Active systems require a supply of external energy. On the other hand, by physical or chemical surface modification, passive systems inherently possess anti-/de-icing characteristics without the requirement of external energy. For this reason, this master thesis focuses on the development of passive anti-icing coatings. One possible new approach to develop passive anti-icing coatings could be to modify surfaces with ice-binding proteins, more specifically anti-freeze proteins (AFPs). These proteins can be found in organisms living in cold climates. They are able to inhibit freezing, thus making life in cold environments possible. Currently, limited research has been performed regarding these AFPs as anti-icing coating material. As a result, this thesis delves deeper into the effect of different environments on the behaviour of AFPs. This is fundamental knowledge that needs to be uncovered before AFPs can be used as an anti-icing material. In a first step, AFPs are directly attached to the surface in various concentrations using a polyethylene glycol (PEG) chain with a specific chain length. From the freezing data, an unexpected phenomenon was observed. It appears that AFP-surfaces freeze faster with increasing AFP concentration. As such, they act as ice promoter instead of the expected ice inhibitor. It is hypothesized that this phenomenon could be largely attributed to the limited protein mobility on the surface. To further test this theory, AFPs with various linker chain lengths were attached to the surface. Indeed, freezing was detected at later time points with increasing linker chain length meaning that AFPs with higher mobility are able to inhibit ice growth. In addition, the incorporationof AFPs showed another interesting phenomenon as well. Ice dendrites on the AFP surfaces appeared to grow more straight compared to their silane-treated counterpart. Because of this, dendrites on the AFP-surfaces were also more easy to blow away. Except for attaching AFPs directly to the surface, their behaviour within a polymeric environment is also studied. For this purpose, various concentrations of AFPs were incorporated within a PEG hydrogel. DSC was used to study the different types of water within the different AFP hydrogels. Interestingly, the amount of freezable bound water increased with increasing AFP concentration. No clear trend could be found between the amount of non-freezing water and the AFP concentration. In addition, freezing tests showed that hydrogels with increasing AFP concentration inhibited ice growth. This behaviour is opposite to the behaviour that was detected for AFPs attached directly to the surface. In a final test, the hydrogels are dehydrated and again subjected to freezing tests. Now, the freezing behaviour follows a similar trend as the AFP-surfaces, meaning that, with increasing AFP concentration, ice formation is promoted. From these results, it is clear that the environment of the AFPs plays a crucial role to the AFP behaviour. Depending on the type of environment in which they are introduced, AFPs can either act as ice inhibitor or ice promotor.

This thesis explores the potential of sustainable resins in composite manufacturing, focusing on bio-based benzoxazine resins and bio-based epoxy derived from brown algae. The research investigates the feasibility of integrating these sustainable alternatives into composite structures. Bio-based benzoxazine resins were synthesized in-house, utilizing m-guaiacol, furfurylamine, sesamol, paraformaldehyde, Jeffamine T403, and DDS, while a commercial bio-based epoxy, phloroglucinol triepoxy (PHTE), was employed. The study involves comprehensive material analysis and testing, including an examination of chemical properties and mechanical performance. The findings reveal contrasting outcomes for the two types of bio-based resins. Bio-based benzoxazine resins exhibited challenges, as curing was not achieved, preventing their combination with composites. In contrast, phloroglucinol triepoxy, the bio-based epoxy from brown algae, emerged as a promising candidate for sustainable composite investigations. This resin demonstrated excellent mechanical properties, although its high viscosity and reactivity posed challenges for traditional manual manufacturing techniques. Furthermore, resin characterization unveiled a high glass transition temperature (Tg) system, especially noteworthy given the use of an aliphatic curing agent and monofunctional reactive diluent that lowers crosslinking density. This opens the door to its application in composites across various industries.

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.

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.

This work presents the design of the HAROLD, a partially wooden electric vertical take off and landing vehicle. The design covers the main aircraft subsystems, while also conceptually sizing a ground station to operate with the aircraft.