Boccarusso, Luca (2017) On the manufacturing techniques of lightweight hemp-epoxy composites and improvement of their flame resistance. [Tesi di dottorato]

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The thesis work has been focused on the study of manufacturing technologies used to produce lightweight hemp/epoxy composites for their future applications as lightweight components, such as in the transportation industry. In this field, apart from the mechanical properties, good flame resistance is also required and then to increase the flame resistance of these components was another goal of this thesis. For this purpose, woven hemp fabrics with large mesh were used to produce porous structures and then lightweight hemp/epoxy composites for their future application both as independent structural components and as core for sandwich structures. The thesis work is structured in the following six sections. The first one begins with an overview on the state of the art of the hemp/epoxy composites and the main concepts about the flame retardants and the flame resistance techniques was presented. In this section, the need to investigate the possible use of hemp/epoxy composite materials, the study of their manufacturing processes (easily applicable for the industrial production) to produce low density composites and the study of techniques able to improve their flame resistance are highlighted. Therefore, an overview about biocomposites, their classification, their advantages and disadvantages, and their manufacturing technologies are reported in the second section. The materials and the methods used to conduct the experimental campaign, both for the manufacturing of lightweight structures and for the improvement of their flame resistance, are presented in the third section, which is structured as follows: -Firstly, a detailed description on the materials and in particular on the hemp fibres is reported; -Subsequently, in order to produce natural fibre reinforced composites with different density values the use of different processes, i.e. infusion, vacuum infusion, brushing hand lay-up and injection moulding were described. To achieve this goal, the section is divided in three sub-sections (Part 1, Part 2 and Part 3); each sub-section is focuses on one of the above-mentioned technologies; -Finally, the methods used to improve the flammability resistance of hemp composites, mixing the epoxy resin with different percentage content of APP (ammonium Poly-phosphate), are described. The subsequent sections of the thesis (Section 4 and 5) focus on the results and the discussion on both the feasibility of the illustrated processes and on the properties of the obtained products. Therefore, a full characterization in terms of tensile, flexural, compression, impact and flame resistance properties are carried out and then discussed. Conclusive remarks, where the main results are summarized, close the thesis work

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