Abstract
Due to their excellent strength-to-weight ratio and flexible processibility, carbon fibre (CF) and its reinforced polymers (CFRPs) have become one of the most attractive materials in various industry structural applications. However, the rapid expansion of CF usage has been accompanied by a growing volume of manufacturing waste and end-of-life composite components, leading to a strong demand for recycling. Recycled carbon fibre (rCF), derived from above discarded materials among various industries, has attracted significant attention due to the increasing demand for "cradle-to-cradle" designs aligned with circular economy. Despite this potential, the high-value reutilization of rCF remains challenging, primarily due to its random fibre distribution, degraded mechanical properties, and limited interfacial performance.To overcome these limitations, appropriate surface treatment and functional modification strategies are required to restore interfacial performance and introduce additional functionalities. In this context, nanomaterials have emerged as an effective solution for enhancing the performance of carbon fibre composites. MXene, known as a novel family of two-dimensional (2D) nanomaterials, has recently attracted much attention in nanotechnology and polymer matrices. Their unique mechanical and electrochemical properties and abundant terminal groups make them ideal for many functional applications. Nevertheless, MXenes also face practical challenges, including easy agglomeration, difficulty in large-scale production and poor macroscopic mechanical properties, which necessitate further structural design, composite strategies, or fine regulation.
Against this backdrop, this research first provides a systematic overview of the most recent developments in CF recycling, MXene material, and CF/MXene matrices or composites, including the preparation, properties, and trends. Different approaches and functional applications, especially detailed in electromagnetic interference (EMI) shielding and electromagnetic absorption, are discussed to highlight the potential of MXene post-treated rCF materials. Furthermore, the existing challenges within the above materials are presented, and the outlook and prospects of this field are also considered.
Building upon these insights, this thesis further exploits the intrinsic anisotropy of rCF to develop a series of MXene/rCF composites with tailored architectures. Specifically, this work has proposed MXene/rCF reinforced polylactic acid (PLA) 3D printing composites, double-layered nonwoven/membrane veils and its composites, fibre array Polydimethylsiloxane (PDMS) composite materials, which follow one-dimensional (1D), 2D, and three-dimensional (3D) ordered structural design principles. Through these designs, their functional applications in the fields such as mechanical properties enhancement, EMI shielding, electromagnetic absorption, flame retardant, thermal conductivity and electrical conductivity enhancement were systematically investigated.
In response to the growing demand for lightweight and flexible EMI shielding driven by artificial intelligence (AI) and fifth-generation (5G) communication technologies, the first part of this work focuses on MXene/rCF-reinforced PLA composites fabricated via electrostatic self-assembly and FDM 3D printing. MXene addition significantly enhances the fibre-substrate interface bonding in fibre-reinforced PLA filaments. This results in the printed parts displaying enhanced toughness, the flexural strength achieved of 105.45 MPa, the modulus of 5.98 GPa, and notched impact strength of 7.12 kJ/m2, realizing 15.6%, 112.1%, and 31.8% improvements, respectively in comparison to pure PLA. Additionally, the modified PLA demonstrates absorption-dominated superior EMI shielding performance. This work offers a viable approach for enhancing rCF-reinforced thermoplastic PLA and insights into designing sustainable, structurally, and functionally integrated composites.
Fibre-oriented structures constructed by 3D printing to enhance the electromagnetic protection properties of plastics, inspired our interest in material structural design. Recognizing the processing limitations and filler-content constraints inherent to FDM-based systems, the second part of this research advances toward lightweight and scalable EMI shielding architectures by constructing MXene/rCF nonwoven fabrics with a double-layered structure via vacuum-assisted filtration (VAF) and hot pressing. To achieve further functional improvements, we also explored the effects of the different MXene types, and the influence of different additives, including conductive adhesives Poly (3,4 ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) and flame retardant Ammonium Polyphosphate (APP). This new MXene/rCF veil shows great potential applications in composite reinforcement fields as a lightweight and scalable EMI shielding material.
To validate the scalability and practical applicability of the nonwoven veil strategy, in third part of thesis, a lightweight, flexible, and functional Ti3C2Tx/PEDOT: PSS /APP rCF veil reinforced composite (MPA-rCFRPs) was fabricated through large-scale VAF and autoclave technology. The modified MPA-rCFRPs have exhibited substantial improvements in EMI shielding with MXene additive amounts as low as 0.24%-1.07%, increasing the EMI shielding effectiveness (EMI SE) to 87.12dB, improved by 350.02%. Remarkably, the through-thickness electrical conductivity of MPA-rCFRPs exhibited a 767.14% improvement, escalating from 19.73 S/m to 151.41 S/m. Meanwhile, the modified composites have exhibited enhanced photothermal, electrothermal, and flame-retardant properties, and the above improvements have not shown a significant impact on the mechanical properties of the material. These results confirm the feasibility of MXene-modified rCF veils for large-scale, multifunctional CFRP systems.
Finally, addressing the increasing demand for efficient electromagnetic absorption, this thesis presents a bio-inspired design based on the symbiotic structure of freshwater sponges and coral polyps. Density-adjustable vertical aligned rCF@Ti3C2Tx/NiFe2O4 arrays embedded in PDMS were fabricated using a convenient electrostatic flocking and self-assembly approach with pretension elastic substrate. Composites enable tunable and highly efficient microwave absorption while avoiding the impact of rCF defects. The results demonstrate that the impedance matching, and loss properties of the material are significantly enhanced by the ordered fibre alignment and the Ti3C2Tx/NiFe2O4 coordination mechanism, leading to exceptional wave absorption performance. By optimizing the array density and thickness, the prepared composites achieved a minimum reflection loss of −60.7 dB and an effective absorption bandwidth of up to 7.82 GHz. This part provides a paradigm for the design of electromagnetic absorption materials utilizing rCF, paving the way for its high-value applications. Overall, this thesis investigates the fundamental properties of rCFs modified with various types of MXene surface treatments. By integrating multiple advanced manufacturing techniques, including 3D printing, nonwoven, autoclave moulding, and electrostatic flocking with thermoplastic and thermosetting polymer matrices, we have developed functionalized rCF composites with 1D filaments, 2D nonwoven mats, and 3D array architecture configurations. The findings reveal that the combination of rCFs with MXene significantly enhances the EMI shielding, electromagnetic absorption performance, flame retardancy, electrical conductivity, and interfacial reinforcement of the composites. Looking ahead, the integration of scalable, eco-friendly MXene production processes holds great promise for enabling the next generation of multifunctional green CF composites, with potential applications in cutting-edge fields such as aerospace, flying vehicles, and humanoid robotics.
| Date of Award | 15 Mar 2026 |
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| Original language | English |
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| Supervisor | Xiaoling Liu (Supervisor) & Gongyu Liu (Supervisor) |