Matrici viscoelastiche per lo stoccaggio e il trasporto di combustibili verdi (combustibili verdi gel)

In the context of the global transition toward cleaner and more sustainable energy systems, reducing fossil fuel dependence has become crucial to mitigating climate change and lowering anthropogenic CO₂ emissions. Among emerging alternatives, fuel gels have attracted growing attention for their unique combination of safety, stability, and energetic efficiency. When applied to aerospace propulsion systems, these materials offer the high energy density required for demanding missions alongside enhanced safety for storage and handling—an essential benefit in aviation and rocket applications where risk mitigation is critical. By incorporating gelling agents into conventional or bio-derived fuels, fuel gels provide improved combustion behavior, reduced volatility, and controllability that facilitate precise fuel injection, leading to safer and more efficient propulsion. Furthermore, when derived from renewable resources, fuel gels present the aerospace industry with a more sustainable pathway toward low-carbon technologies, helping align aviation and spaceflight with global climate goals. Within this framework, carbohydrate-based fuel gels represent a particularly promising class of soft materials with applications spanning renewable energy, transportation, military, and emergency systems. Their performance is governed by the interplay between molecular interactions, gelation mechanisms, and thermal stability. This research focuses on the design, characterization, and optimization of alcohol-based fuel gels. Methanol and ethanol were chosen as alcohols, whereas methylcellulose (MC) and ethyl cellulose (EC) were employed as thickening and gelling agents. The influence of calcium chloride (CaCl2) as a structuring and performance-enhancing additive was also investigated. In addition, preliminary tests were carried out to evaluate the feasibility of formulating biodiesel-based gels. For methanol-based gels, rheological analyses showed that methylcellulose forms stable gels at concentrations above 22 wt%, as a result of viscoelastic phase separation driven by a lower critical solution temperature (LCST). Thermogravimetric studies confirmed good thermal stability with a single-stage decomposition, while the addition of CaCl₂ significantly altered the rheological and thermal behaviour and improved both combustion and ignition performance of the systems. These effects are attributed to the formation of CaCl₂–methanolate complexes, which influence nanoscale aggregation, correlation length, and fractal structure, as confirmed by small-angle X-ray scattering (SAXS). For ethanol-based gels, rheological analyses revealed that pure EC in ethanol exhibited liquid-like behaviour, whereas gelation occurred only when the EC-to-CaCl₂ ratio reached 2:1 and suitable concentrations of both components were employed. At this composition, thermogravimetric analysis indicated enhanced ethanol retention at elevated temperatures and a single-step EC decomposition process. In the optimised formulation, the activation energy for EC degradation was the highest, while ethanol ignition remained efficient, resulting in a total combustion energy density comparable to that of pure ethanol, but with the advantages of improved handling and enhanced safety. Biodiesel-based gels exhibited a progressive transition toward gel-like behaviour with increasing concentrations of both EC and CaCl₂, highlighting the promising potential for the development of biodiesel-based fuel gels. Overall, the findings demonstrate that the addition of CaCl₂ offers assisted ionic coordination, which is an effective and versatile strategy for the design of thermally stable, tunable, and energy-dense cellulose-based fuel gels. The insights gained into their microstructural organization, rheological performance, and combustion behaviour provide a scientific foundation for the development of next-generation sustainable fuel materials and advanced energy composites, contributing to the broader transition toward green and efficient energy systems.