Epoxy resins have long been recognised as key thermosetting materials in advanced engineering due to their excellent thermal and mechanical performance, ease of processing, and strong adhesion to a wide range of substrates. These qualities have encouraged their widespread adoption in demanding sectors such as aerospace, electronics, automotive engineering, civil engineering, and electrical systems, as well as in the manufacture of high-performance composite materials. However, beyond their technical advantages, these resins present structural and environmental limitations that have driven an active search for more sustainable alternatives.

Most commercial epoxy resin formulations are based on monomers derived from fossil resources, particularly diglycidyl ether of bisphenol A (DGEBA), a non-renewable molecule associated with risks to human health, including endocrine disruption and reproductive toxicity. Furthermore, the polymer networks formed during curing are highly crosslinked and chemically irreversible, preventing subsequent recycling or reprocessing. This lack of circularity contributes to the accumulation of thermoset waste that is difficult to manage. In addition, these materials are inherently flammable; when they burn, they release large amounts of heat and emit toxic gases, compromising safety in critical applications. These limitations not only affect the technical performance of the material but also have direct implications for compliance with emerging environmental regulations, such as European Union policies on chemical use and waste management.

Carbon fibre reinforced polymers (CFRPs) are valued for their light weight, stiffness, and durability, making them indispensable in industries such as aerospace, rail transport, wind energy, and defence. However, most current CFRPs rely on conventional thermoset matrices, inheriting the same shortcomings in recyclability, flame retardancy, and sustainability. This restricts their evolution towards genuinely environmentally responsible solutions and creates significant challenges in terms of regulation and circularity. As sustainability requirements continue to increase across industrial sectors, the need for functional and responsible alternatives becomes ever more urgent.

In response to this context, the present thesis focuses on the development of new recyclable, flame-retardant, and bio-based epoxy vitrimer matrices specifically designed for use in CFRPs. The design strategy is based on introducing dynamic imine bonds into the epoxy network. These bonds enable reversible reactions such as transimination and hydrolysis-reformation, providing the material with thermal reconfiguration, self-healing, and chemical recycling capabilities. At the same time, the incorporation of phosphorus-containing groups and aromatic structures promotes char formation during combustion, contributing to greater thermal stability and enhanced flame-retardant behaviour. These functionalities not only address technical demands but also open new possibilities for end-of-life management of composite materials.

The choice of imine bonds as the dynamic unit in this research was not arbitrary. Imine bonds, formed through the condensation of a carbonyl group and an amino group, possess a structure that is relatively stable under ambient conditions but exhibits a unique ability to break and reform under mild stimuli, such as heat or the presence of nucleophiles. This characteristic makes them particularly attractive for introducing reversibility into thermoset systems without compromising the structural integrity of the material during its service life. Unlike other dynamic bonds, such as esters or urethane-disulphides, imine bonds offer tunable exchange rates and synthetic compatibility with a wide range of bio-based compounds. Furthermore, their incorporation into epoxy networks does not require external catalysts, simplifying formulation processes and reducing associated costs. From an environmental perspective, many imine-bond precursors, such as aromatic amines or natural aldehydes (for example, vanillin), can be obtained from renewable sources, aligning this approach with the principles of green chemistry. It has also been demonstrated that imine-based vitrimers retain their functional properties even after multiple recycling cycles, ensuring long-term material stability without significant performance loss. For these reasons, imine chemistry stands out as one of the most promising strategies for designing high-performance reversible thermosets.

Triglycidyl ether of glycerol (Gte), a bio-based epoxy resin free from bisphenol A structures, was selected as the base resin. Three different vitrimer systems were designed and studied from this monomer, covering the entire process from component synthesis through processing, characterisation, and final evaluation in carbon fibre reinforced composites. The selection of Gte was deliberate, as its low molecular weight, high functionality, and renewable origin make it an attractive platform for sustainable formulations with good mechanical properties.

Chapter 4 describes the development of the GVD system, formulated from Gte, an imine curing agent derived from vanillin and p-aminophenol (VA), and the phosphorus-containing additive DOPO. To prevent side reactions between DOPO and the functional groups involved in curing, the additive was first incorporated into the epoxy chain. The GVD system demonstrated remarkable flame-retardant performance, achieving a UL-94 V-0 rating and a limiting oxygen index (LOI) of 31%. Cone calorimetry tests revealed significant reductions of 38.2% in peak heat release rate (pHRR) and 26.3% in total heat release (THR). Furthermore, the system exhibited functional properties such as thermal reshaping, shape memory, and recyclability, confirming the successful formation of a dynamic imine-crosslinked network. The results obtained at this stage provided a solid foundation for exploring more complex and robust formulations.

Chapter 5 addressed one of the weaknesses observed in the Gte-VA system: its limited crosslinking density under melt-processing conditions. To overcome this issue, a rigid aromatic comonomer, tris(trihydroxyphenyl)methane triglycidyl ether (Tmte), was incorporated to increase stiffness and improve mechanical performance. The resulting hybrid system, designated GTV, displayed a balanced combination of flexibility and strength. The optimal formulation (GTV-4) achieved a glass transition temperature (Tg) of 91.1°C, a tensile strength of 73.4 MPa, and a Young’s modulus of 1069 MPa. It also retained vitrimer characteristics such as self-healing, thermal reshaping, and shape memory. This system was successfully processed into solvent-free prepregs and used to manufacture CFRPs. The laminated specimens could be selectively degraded in an ethylenediamine solution at 60°C, allowing complete recovery of the carbon fibres without damage. This procedure, which does not require toxic solvents or extreme conditions, represents a significant contribution towards more accessible recycling technologies.

Chapter 6 focused on solving the practical challenges associated with the high reactivity and narrow processing window of the previous systems when applied to continuous melt-prepreg production lines. To address this issue, a new curing agent containing imine bonds, phosphorus groups, and hydroxyl functionalities, named FROH, was designed and synthesised. This trifunctional curing agent was produced through a two-step route: condensation of POCl₃ with vanillin, followed by reaction with p-aminophenol. The Gte-FROH system exhibited stable rheological behaviour and curing kinetics compatible with industrial equipment. Based on this formulation, a semi-automated continuous melt-prepreg production system was developed, achieving homogeneous impregnation and stable handling characteristics. The final carbon fibre reinforced composite (Gte-FROH-CF) reached a flexural strength of 1024.5 MPa and obtained a UL-94 V-0 classification. Most importantly, the system enabled complete fibre recovery under mild conditions, confirming its potential as a recyclable and safe alternative for industrial processes. Moreover, this methodology demonstrates the feasibility of integrating such systems into real-scale manufacturing operations, a crucial step towards technological transfer.

Overall, this thesis establishes a comprehensive design and validation strategy for the development of high-performance, sustainable, and functional epoxy vitrimer systems suitable for advanced structural applications. The introduction of dynamic bonds, combined with flame-retardant elements and copolymerisation approaches, enabled the overcoming of several critical limitations of traditional epoxy resins. From a scientific perspective, the results provide deeper insight into how chemical structure influences properties such as reprocessability, thermal behaviour, and mechanical performance. From a technological standpoint, the work demonstrates the feasibility of manufacturing prepregs using sustainable techniques without compromising final product quality.

It is worth highlighting that the methodologies proposed can be extended to other thermosetting polymers, creating new opportunities for implementing circular solutions in fields where recycling remains a significant challenge. Adaptive molecular design based on dynamic bonds and strategically incorporated functional groups represents a promising pathway towards smart materials capable of combining durability, safety, and environmental responsibility. In an industrial context characterised by strict regulations and increasing functional requirements, the vitrimer systems developed here offer a versatile and robust platform with the potential to transform the composite materials landscape in a technological environment increasingly focused on sustainability and circularity. Furthermore, their adaptability to industrial processes and compatibility with existing composite manufacturing techniques position them as a realistic and scalable alternative for a new generation of sustainable structural materials. Ultimately, this research lays the foundations for a transition towards more responsible production models with lower environmental impact and greater long-term benefits for both industry and society.