Vitrimers represent a class of polymers featuring dynamic covalent crosslinks that can undergo dynamic network rearrangements and hold a notable promise as recyclable thermosets with crack-healing capabilities. In particular, vitrimers with aromatic disulfide hardeners have emerged over the past few years. In these high-glass-transition polymers, the healing regime coincides with the onset of thermal degradation, posing a fundamental challenge for reconciling adequate network mobility with thermal degradation prevention. Therefore, the present study explores the repair capabilities of glass fiber-reinforced polymers (GFRP) with a vitrimer matrix to understand how the interplay of temperature, time, and pressure affects the repair. A transferable framework for estimating a favourable time-temperature regime for vitrimer healing is introduced, based on thermal degradation and dynamic bond-exchange kinetics. The suggested optimized conditions are applied to repair different GFRP samples subjected to quasistatic intralaminar crack opening, and the extent of apparent mechanical property recovery is used to assess the repair effectiveness. Pressurized reconsolidation is required to restore the microstructure and repair cracks. When applying the prescribed repair conditions to the specific damage in short-beam samples, remarkable stiffness and strength recovery ratios of 93 % and 80 %, respectively, are achieved. Conversely, deviations from the prescribed regime due to improper dwell temperatures and times considerably reduce the recovery ratios of mechanical properties, limiting them to their residual values. However, the double cantilever beam repair conducted within the favourable regime shows that repair effectiveness depends strongly on the fracture surface morphology, revealing inherent limitations in the repair capabilities of the investigated laminate system.

This study explores the development of sustainable bamboo fiber-reinforced bio-based polycarbonate (BF-PC) composites. Prepreg laminates were fabricated using solvent-based impregnation and compression molding. The effects of chemical surface modifications—alkali and silane—on bamboo fiber properties, interfacial bonding, and composite performance are studied and supplemented by comprehensive characterization, including FTIR, SEM, fiber density, single fiber tensile testing, cross-sectional microscopy, void fraction analysis, and tensile and flexural testing. Results revealed that 2 g/L silane-treated fibers showed the highest improvements in mechanical properties and interfacial adhesion, achieving tensile and flexural strengths of 162 MPa and 184 MPa, respectively. In contrast, alkali treatments failed to improve bonding and resulted in lower composite performance. In summary, surface chemistry of natural fibers and circular buildings, circular composites, natural fibre composites, renewable composites, renewable matrixcomposite processing play a crucial role in renewable polycarbonate matrix composite engineering.

The drawback of biobased polymer matrix composites (PMCs) is their limited temperature stability, resulting from degradation, which restricts their processability in established composite manufacturing processes requiring elevated temperatures. These key issues not only affect the mechanical properties but ultimately limit the utilization of flax fibers as fiber reinforcement in PMCs. In this study, kinetic models for the thermal degradation of flax fibers and PA11 are derived and combined with a model for thermo-chemical fiber degradation. Selective degradation of the fibers and mechanical testing establishes a link between degradation and the accompanying deterioration of the mechanical performance. The deterioration of flax fiber mechanical properties under concurrent thermal and thermo-chemical degradation is primarily governed by the thermos-chemical contribution (chain scission) up to 3% thermal degradation, beyond which the influence of thermal degradation becomes evident. Even 1% thermal degradation of flax fibers results in a pronounced reduction in their mechanical performance. In contrast, equal degradation values enhance the PMCs' strength, which may be attributed to improved fiber-matrix interactions. Compiling results into processing maps establishes a framework for designing tailored processing of temperature-sensitive materials, offering transfer opportunities to individual processing conditions and heat treatments, enabling broader research on bio-based PMCs.

Sustainable polymers are essential to reducing the environmental impact of conventional plastics. While the use of renewable feedstocks plays a significant role, the adoption of green processes, including sustainable solvent selection and efficient polymer purification, is equally essential. This study presents a green synthesis route for polymers based on two renewable vinyl lactone monomers: α-methylene-γ-valerolactone (MeGVL) and α-methylene-γ-butyrolactone (MeGBL). Polymerization was performed in renewable solvents as Cyrene®, γ-valerolactone, and 2-methyltetrahydrofuran via solution and in biobased alcohols through precipitation methods. While solution polymerization requires additional purification step through polymer precipitation, precipitation polymerization enables efficient polymer recovery and solvent reuse. The resulting polymers made via precipitation polymerization exhibit properties with glass transition temperatures of 99 °C (polyMeGVL) and 94 °C (polyMeGBL), and visible light transmittance over 96% between 450-700 nm of both polymer films of thickness around 100 μm. Water contact angles of the films were 62° for polyMeGVL and 51° for polyMeGBL showing difference despite having a similar chemical composition. These results highlight a scalable, low-impact pathway for producing commodity polymers entirely from renewable resources.

Coordinating and executing an MSc program is accompanied by various challenges. To name a few: a) students joining the program means have diverse backgrounds which means varying levels of prior knowledge, and b) in a program that offers specialization into different profiles, it is important to ensure that every student attains the required breadth in foundation as well, which the program mandates. At the Aerospace Structures and Materials (ASM) Department in the Faculty of Aerospace Engineering at TU Delft, we are developing a core curriculum that encompasses the first education quarter (8 weeks, 15 ECTS), which aims to successfully tackle these challenges in order to train up future aerospace engineers with solid technical foundation, critical thinking ability and collaborative working spirit. The module starts with a “soft-landing” for the students and is followed by three content sprints that cover the essentials in the three principal domains of ASM – Materials, Manufacturing and Modelling. Engineering and consulting assignments have been embedded that tie the sprints together and offer inspiration and motivation for the students. In parallel, students get trained in transversal skills. A student facing dashboard will provide comprehensive feedback on learning progress and outcome. The dashboard will additionally support the transition towards a portfolio-based assessment. In this paper, we outline key features of the core curriculum along with the process that was employed for its development.

Polymer membranes are prime candidates for separation and purification processes, with their functionality enhanced by nanoparticle incorporation and diverse polymer structures. Poly(ionic liquids) (PILs), highly charged electrolyte-like polymers, are gaining interest as membrane polymer matrices. Embedding photocatalytic nanoparticles enables water purification through filtration and degradation reactions. Graphitic carbon nitride (g-CN), a metal-free semiconductor with visible-light activity, offers a promising approach for photoredox-based environmental remediation, though its powder form poses separation challenges. This work presents g-CN embedded PIL nanocomposite membranes fabricated via UV curing, characterized by structural, filtration, and surface properties. Photocatalytic performance and reusability under visible light are evaluated using methylene blue (model dye) and sulfadiazine (model antibiotic) under static conditions. A continuous filtration module with integrated light is developed to assess simultaneous filtration, degradation, and antifouling properties, demonstrating the membranes’ potential for advanced water treatment.

Tactix 742 (a trifunctional aromatic epoxy resin) is a benchmark epoxy monomer elucidating the highest T_gepoxy resin system; however, its manufacturing relies on petroleum-based toxic chemistries. In the realm of sustainability, potential replacement of Tactix 742 with a renewable platform possessing similar thermomechanical properties as well as processing character is critical. The resin system of renewable resveratrol triglycidyl ether with aerograde hardener 4,4-diaminodiphenylsulfone shows an ultrahigh T_gof 324 °C and mechanical properties comparable to the industrially used petro-based tris(hydroxyl phenyl)methane epoxy monomer. The results highlight the untapped potential that biobased molecules show in innovating existing high-performance plastic formulations while potentially increasing sustainability potential in the future. Resveratrol triglycidyl ether-4,4-diphenyldisulfone (RTE-DDS) formulation shows T_g, stiffness, strength, and processing behavior similar to that of the industrially used petro-equivalent formulation (T742-DDS) with slightly lower modulus and strength in both tensile and flexural testing. Fracture toughness of the biobased formulation is 61% higher than the petro-based formulation. CFRP manufacturing yields high-quality composite materials tested in compression, interlaminar shear, and in-plane shear modes. Fiber volume content is slightly lower than ideal due to the formulations high viscosity and the choice of vacuum bagging and autoclave manufacturing technique, but low void content of 0.55% ± 0.26 allows for accurate characterization of CFRP laminates. Conclusions are drawn regarding the future potential of resveratrol epoxy monomer in high-performance epoxy CFRPs.

Vitrimers are a class of polymer networks featuring dynamic covalent crosslinks that can undergo associative bond exchange. These dynamic polymer networks hold a notable promise as recyclable thermosets with self-healing capabilities, provided by network rearrangements at the molecular level, allowing for macroscopic flow. When the relaxation time is sufficiently short, vitrimer material behaves like a thermoplastic even though it is covalently crosslinked. However, temperature-induced malleability remains limited by the high-viscous nature of vitrimers. Therefore, the present article explores the cure dependence of structural relaxation and vitrimer transition phenomena of a dynamic disulfide-containing epoxy vitrimer. Stress relaxation measurements reveal that intermediate cure states—accompanied by lower crosslinking density—exhibit bond exchange and segmental relaxation rates exceeding those of fully cured networks over an order of magnitude. This enhanced dynamics facilitates lower viscosities and residual times during high-temperature malleability processing. Advanced methods combining rheology, cure kinetics, and thermomechanical analysis are utilized to assess the cure dependence of the vitrimer transition temperature (Formula presented.). We outline a distinct cure dependence of (Formula presented.), which may be approximated by a linear correlation, suggesting that viscoelastic flow can be initiated at significantly lower temperatures in undercured networks. These findings provide valuable guidance for enhancing material and processes, contributing to opening doors to the “melt processing” of this family of materials.

The following study cements vanillin’s position as a leading replacement for BPA-based epoxy resins in high performance epoxy–amine composite applications. Diglycidyl ether of vanillyl alcohol (DGEVA) is cured with a high-performance aerospace grade crystalline diamine hardener 4,4 diaminodiphenyl sulfone (4,4-DDS) yielding a resin with a Tg of 140 °C according to DMA, high bending stiffness of 3.84 ± 0.02 GPa, and high mode I fracture toughness of 1.33 ± 0.23 MPa m1/2, as evidenced by ASTM standard tests. Initial kinetic and rheological evaluation of DGEVA–DDS highlights its potential to act as a drop-in epoxy system for many industrial composite manufacturing processes with minor processing adjustments. Resin is characterized by means of cure kinetics, thermomechanical properties and physical properties deciphering a route for carbon fibre reinforced composite manufacturing. The results show superior performance of the neat DGEVA–DDS system in mechanical tests including up to 38% greater strength, 60% stiffness, 160% fracture toughness, and minor increases when translated to composite materials as compared to BADGE–DDS.

The present article introduces a high-performance epoxy vitrimer to target structural composite applications. By utilizing a reactive diluent derived from biobased feedstock, the maximum glass transition is tailored to maintain a sufficient temperature window for reprocessing, avoiding the degradation of permanent bonds. Different fractions of permanent cross-links are imbued into the network structure, and the hybrid network is elucidated by creep and stress relaxation. The creep behavior at service temperatures below 150 °C remains unaffected, while slower bond exchange dynamics and higher extrapolated topology freezing temperatures T_v are reported for an increasing number of permanent cross-links. Comprehensive studies of physicochemical, thermo-rheological, and curing reactions are carried out and summarized in a conversion-temperature phase diagram first reported for a vitrimer. The vitrimers show great malleability, even with permanent cross-link fractions above the theoretical limit for a percolated network formation, and we demonstrate recycling by comminuting and subsequent reconsolidation. These findings provide valuable guidance for enhancing material and process development of high-performance vitrimer resins and lay the groundwork for advancing composites built on vitrimer matrix systems.

Metal-free graphitic carbon nitrides are on the rise as polymer photocatalysts under visible light illumination, taking shares in a range of promising photocatalytic reactions, including water splitting. Their simple synthesis and facile structural modification afford them exceptional tunability, enabling the creation of photocatalysts with distinct properties. While their metal-free nature marks a significant step towards environmental sustainability, the high energy consumption required to produce carbon nitride photocatalysts remains a substantial barrier to their widespread adoption. Furthermore, the process of condensation at approximately 550 °C typically results in solid yields of less than 15 %, significantly challenging their economic viability. Here, we report on lowering manufacturing conditions of carbon nitride photocatalysts whilst enhancing photocatalytic activity by introducing binaphthyl diamine as a structural mediator. At 450 °C in 2 hours, carbon nitride photocatalyst shows a lower bandgap and enables visible light induced hydrogen evolution (194 μmol h⁻¹) comparable to benchmark carbon nitride photocatalysts.

Epoxy resins have been used as composite matrix materials for over half a century, enabling lightweight materials for a variety of applications. Their properties including high strength, chemical resistance, and ease of processing feature them as prime candidates for composite applications. Currently, high performance epoxy monomers are derived from non-renewable feedstocks, which presents a problem for future generations and technologies regarding sustainability. Many bio-based alternatives have been investigated, but properties fall short of high-performance industry standards due to a lack of appropriate chemical groups. Herein 3 bio-based epoxy monomers, with potential to replace high-performance standards, are compared against 3 petroleum derived industry standards. Industrial high performance aromatic diamine crystalline hardener is used to synthesise resin systems. Tensile, flexural and fracture toughness properties are investigated following ASTM standards. Beyond a practical investigation of the physical properties of these resins a comparison of chemical structure to mechanical properties is made. Free volume investigations using positron annihilation lifetime spectroscopy (PALS) were performed, and can be used to explain to some degree the observed properties of the resin systems.

The development of epoxy resin formulations from renewable feedstocks has been thoroughly explored in the chemical literature. A simple one-pot chemical reaction involving sustainable phenolic molecules and epichlorohydrin results in the production of renewable epoxy monomers. These monomers can be cured with amines or anhydrides to yield cross-linked thermosetting resins. Although a wide variety of recipes exist, there is a notable gap in the application of these sustainable resin formulations to engineering contexts. This gap is primarily due to the lack of comprehensive, standardized analyses of these resin recipes, which impede their potential use in advanced composite applications. In this study, we reveal a high-performance resin formulation utilizing epoxidized phloroglucinol derived from brown algae in combination with an aerospace-grade amine hardener. The resin processing and thermomechanical properties are investigated using ASTM standard tests including tensile strength, flexural strength, fracture toughness, and interlaminar shear strength. Given the detailed comparative analysis, the partially renewable resin recipe outperforms petroleum derived analogues.

The present study describes the development of cure kinetics and chemo-rheological models for an epoxy vitrimer based on polyimine exchange to elucidate the potential in terms of processing and accurate process selection. Reaction kinetics is investigated using differential scanning calorimetry. A good agreement between the model and data can be demonstrated for different stoichiometries by selecting a parallel reaction approach consisting of an nth-order and an autocatalytic approach. The suggested chemo-rheological model captures the intrinsically high viscosity of the resin over a broad temperature and curing range, even after the gelation point. The Di-Benedetto equation represents the glass transition temperature advancement with cure while combining the rheological Winter-Chambon criterion and the kinetic model determines the degree of cure at the gelation. These results give important advice for improved process modeling of vitrimeric resins, facilitate accurate process selection, and pave the way towards the development of composites based on the matrix system investigated in this work.

In this work, we pioneered the preparation of diamond-containing flexible electrodes using 3D printing technology. The herein developed procedure involves a unique integration of boron-doped diamond (BDD) microparticles and multi-walled carbon nanotubes (CNTs) within a flexible polymer, thermoplastic polyurethane (TPU). Initially, the process for the preparation of homogeneous filaments with optimal printability was addressed, leading to the development of two TPU/CNT/BDD composite electrodes with different CNT:BDD weight ratios (1:1 and 1:2), which were benchmarked against a TPU/CNT electrode. Scanning electron microscopy revealed a uniform distribution of conductive fillers within the composite materials with no signs of clustering or aggregation. Notably, increasing the proportion of BDD particles led to a 10-fold improvement in conductivity, from 0.12 S m^-1 for TPU/CNT to 1.2 S m^-1 for TPU/CNT/BDD (1:2). Cyclic voltammetry of the inorganic redox markers, [Ru(NH₃)₆]^3+/2+ and [Fe(CN)₆]^3-/4-, also revealed a reduction in peak-to-peak separation (ΔE_p) with a higher BDD content, indicating enhanced electron transfer kinetics. This was further confirmed by the highest apparent heterogeneous electron transfer rate constants (k⁰_app) of 1 × 10^-3 cm s^-1 obtained for both markers for the TPU/CNT/BDD (1:2) electrode. Additionally, the functionality of the flexible TPU/CNT/BDD electrodes was successfully validated by the electrochemical detection of dopamine, a complex organic molecule, at millimolar concentrations by using differential pulse voltammetry. This proof-of-concept may accelerate development of highly desirable diamond-based flexible devices with customizable geometries and dimensions and pave the way for various applications where flexibility is mandated, such as neuroscience, biomedical fields, health, and food monitoring.

Twin matrix composites (TMC) are novel composite architectures where reinforcing composite elements are embedded in a secondary resin to address various mechanical functions suited for diverse engineering applications such as morphing wings. Here, for the first time, a recyclable twin matrix composite using micro-pultruded rods as reinforcements will be manufactured. Within the scope of the work, the design of the TMC mould which allows 0°/90°/0° reinforced layup will be discussed and created through additive manufacturing. Recycling and remanufacturing TMC will be conducted up to 4 times, and surface characteristics of the rods will be examined to monitor the effect of recycling. Interlaminar shear strength of TMC made from fresh and recycled rods will be investigated comparatively.

Two-dimensional (2D) materials have great potential in macromolecular synthesis, yet there are some areas that still need to be explored, such as anionic polymerization. In this study, we present the first example of photoinduced anionic polymerization of ethyl-2-cyanoacrylate (ECA) using 2D graphitic carbon nitride (g-C₃N₄) as an active photocatalyst responsive to visible light. Our results demonstrate that particularly the mesoporous structure of g-C₃N₄ can initiate polymerization through the generation of electron-hole pairs upon exposure to visible light. To have a better insight into mechanistic pathways, several experiments, including control experiments, are conducted. The obtained polymers and the synthesized g-C₃N₄ materials are characterized comprehensively by chromatographic, thermal, and spectroscopic techniques. Accordingly, this study demonstrates an innovative process that can offer several advantages over traditional polymerization methods, including the ability to initiate polymerization at ambient temperatures and achieve high polymerization rates.

Over the past 30 years, the polymer composite industry has flourished, producing advanced structural materials for the aviation, energy, and transportation sectors. However, the use of crosslinked thermoset matrices has been linked to significant end-of-life challenges, presenting a critical issue for the industry. Moreover, the industry is characterized by numerous labor-intensive processes. In alignment with Industry 4.0 principles, two major routes have been identified to enhance sustainability: the utilization of high-performance thermoplastic matrices and the integration of artificial intelligence in manufacturing. Nevertheless, there are substantial concerns regarding the life cycle assessment of these technologies, which are not accounted for in the initial calculations, including the environmental footprint of polymer synthesis and energy requirements for training AI. This perspective aims to address potential and significant CO₂ emissions from chemical feedstocks and the high computing requirements of these new technologies.

Utilization of sustainable feedstocks to fabricate renewable thermosetting epoxy resins has been of great interest recently; however, their translation into composite structures and benchmark comparisons are poorly understood. Phloroglucinol is a phenolic molecule obtained from brown algae, and its epoxidized form is a high viscosity, high reactivity monomer. In this study, the potential of epoxidized phloroglucinol as a laminating resin was examined in comparison with a bisphenol A diglycidyl ether (BADGE) epoxy monomer employing the Epikure 04908 linear amine hardener system. Utilization of a reactive diluent for PHTE resin was necessary for room temperature laminating applications to reduce viscosity, and the thermomechanical properties of PHTE-based resins and composites are superior to those of BADGE systems.

Developing high-performance carbonaceous anode materials for sodium-ion batteries (SIBs) is still a grand quest for a more sustainable future of energy storage. Introducing sulfur within a carbon framework is one of the most promising attempts toward the development of highly efficient anode materials. Herein, a microporous sulfur-rich carbon anode obtained from a liquid sulfur-containing oligomer is introduced. The sodium storage mechanism shifts from surface-controlled to diffusion-controlled at higher synthesis temperatures. The different storage mechanisms and electrode performances are found to be independent of the bare electrode material's interplanar spacing. Therefore, these differences are attributed to an increased microporosity and a thiophene-rich chemical environment. The combination of these properties enables extending the plateau region to higher potential and achieving reversible overpotential sodium storage. Moreover, in-operando small-angle X-ray scattering (SAXS) reveals reversible electron density variations within the pore structure, in good agreement with the pore-filling sodium storage mechanism occurring in hard carbons (HCs). Eventually, the depicted framework will enable the design of high-performance anode materials for sodium-ion batteries with competitive energy density.