Esposito, Claudio (2025) Carbohydrate-based foam as green and biodegradable packaging material. [Tesi di dottorato]

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Abstract

This Ph.D. dissertation presents an in-depth study of the extrusion foaming of starch, with a focus on optimising die design and managing shape instability during the process. The research integrates experimental investigations and computational fluid dynamics (CFD) simulations to investigate how processing conditions, die geometry, and material properties influence the quality and stability of foamed extrudates. Focusing on starch, a renewable, bio-based, and biodegradable material derived from sources such as potatoes and corn, the research highlights the potential of starch-based foams as a sustainable alternative to fossil-based materials such as expanded polystyrene (EPS) and expanded polypropylene (EPP), which are commonly used in packaging and other industries. However, the extrusion of starch-based foams presents challenges related to moisture content and die swelling. The main challenge addressed is die swell, also known as the Barrus effect, which causes irregular swelling at the die exit, resulting in distortion and inconsistencies in the final product. To mitigate this problem, a fluid dynamics model was developed to predict the final shape of the extrudate by simulating die geometry, flow conditions, and material behaviour, significantly reducing trial-and-error iterations in die design. The simulations have been validated with experimental data, improving the accuracy of predictions of extrudate shape and foam behaviour. Through this integrated approach, the thesis provides valuable insights into the role of die design in improving the extrusion process and advancing the development of starch-based foams for various applications. In addition, the research incorporates advanced 3D printing techniques to further explore foam structure and morphology. One of the key findings was the discovery of dual-orientation bubble morphology in 3D-printed foams, where bubbles are orientated both in the extrusion direction and radially. This behaviour, which is influenced by processing parameters such as extrusion temperature, provides new insights into bubble formation and foam microstructure. The second finding relates to the 3D printing process for plant-based meat alternatives. In particular, the research demonstrates the potential of manipulating process parameters (printing velocity and temperature) to achieve a specific internal morphology in terms of bubble number and size. This allows material properties to be controlled through parameter adjustments, rather than relying on complex ink formulations, and has important implications for tailoring foam properties for specific applications in industries such as food, packaging, and materials science.

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