Phd in AERONAUTICS AND SPACE ENGINEERING

Thesis title: Study of a closed-loop process for recycling high-performance thermoset epoxy/carbon fiber composites

Fiber reinforced polymers are widely used across various industries due to their exceptional mechanical properties and low material density. In recent decades, their application has been steadily increasing and is expected to continue growing. However, these materials have a typical lifespan of around 25–30 years, leading to a rising volume of end-of-life polymer composites that require effective disposal or recycling strategies. Currently, a significant portion of these materials is either incinerated or landfilled, posing substantial environmental concerns. Consequently, extensive research efforts have been directed toward identifying optimal recycling approaches, with solvolysis emerging as a promising method for recovering valuable fibers while minimizing degradation. Solvolysis, a form of chemical recycling, involves the dissolution of the polymer matrix to extract fibers with minimal damage. This approach is particularly appealing for carbon fiber-reinforced composites due to the high environmental and economic costs associated with virgin fiber production. However, challenges remain in optimizing reaction conditions to enhance the efficiency and viability of solvolysis on a larger scale. In this study, a solvolysis method using an aqueous sulphuric acid solution has been developed and optimized to recover high-quality carbon fibers from epoxy resin composites. Key process parameters, including solution concentration, temperature, residence time, and fluid agitation, were systematically adjusted to maximize fiber recovery while minimizing property degradation. The study also explored the influence of porosity and fiber volume fraction on solvolysis efficiency. A numerical model was developed to analyze these effects which were also analyzed experimentally. The effectiveness of the solvolysis process was assessed using Fourier-transform infrared spectroscopy and scanning electron microscopy to analyze the chemical and morphological impacts on the recycled fibers. Furthermore, composites manufactured with the recovered fibers retained 65–95% of the mechanical properties of those made with virgin fibers. The most significant reduction was observed in tensile modulus, whereas flexural properties were largely preserved. Additionally, the potential for using recycled carbon fibers in space applications was investigated. Composite materials reinforced with recycled and virgin carbon fibers were subjected to UV-C irradiation to assess structural performance, surface morphology, and chemical modifications. The results demonstrated that recycled fibers could be effectively utilized in satellite platforms without significant performance degradation. To evaluate the environmental benefits of the proposed recycling approach, a life cycle assessment of recycled fibers was conducted. The findings indicate substantial improvements in several environmental impact indicators when compared to the production of virgin carbon fibers.