Faggio, Noemi (2024) Design and development of furan-based epoxy resins and their applications as advanced materials. [Tesi di dottorato]

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Abstract

Nowadays, environmental concerns on the use of polymeric materials, related to a plastic waste reduction, lead to a responsible use of these materials and a forecast on the end-life workpieces disposal. Moreover, in the perspective of environmental impact reduction, the use of non-renewable materials is highly discouraged. For this reason, the scientific and industrial community is focused on the development of new bio-based polymers. In this framework, this research work is aimed to investigate the products and the potential applications of different renewable furan based epoxy resins cured with bio-based hardeners. First, a deep discussion on the state of art, regarding the current synthesis of bio-based epoxy monomers and curing agents, is proposed. Then the synthesis of a new furan based epoxy monomer, identified with name 2,5-bis[oxiran-2-ylmethoxy)methyl]furan (BOMF), provided by the extraction from polysaccharides is carried out. It was then cross-linked through the appropriate choice of green crosslinking agents, the first case study regards the use of maleic anhydride (MA) as curing agent in order to generate a resin with enhanced adhesive properties for carbon fiber reinforced plastic joints. The same combination is investigated for nanofibers production through electrospinning with the aim to assembly bilayer filters for fluids. In the second case study, another curing agent, isophorone diamine (IPD), was used to produce nanocomposites with different contents of carbon nanotubes, which have the objective to improve the electro-thermal properties of nonconductive commercial fabrics. The discussion on the choice of curing agents is crucial regarding the environmental impact of these resins. Maleic anhydride (MA), which is not impacting on the environment and isophorone diamine (IPD) which gives excellent mechanical properties and reaction kinetics, has been selected. The epoxy resins obtained have been characterized from the thermal, mechanical, rheological and morphological point of view and used in different fields of application such as adhesives for composites, protective nanofibers for commercial membranes, nanocomposites and conductive and thermoresponsive textiles. The various tested epoxy and hardener combinations has proven to preserve an high renewable content. In comparison with a commercial epoxy resin, the mechanical properties of the system BOMF/MA are lower, especially which regards tensile strength and stiffness, but there was obtain an exceptional improvement in to use as adhesive for composites due to more flexible behavior. The same system was used to obtain electrospun nanofibers and they exhibited uniformity, lack of defects and high resistance to chloroform washing, which made them very suitable for the employ in bilayer membranes for fluid filtering. The latter system, BOMF/IPD in combination with carbon nanotubes, has proven to have outstanding and repetable electrothermal properties to be used in fabric coating with the aim to potentially introduce this production in biomedical devices. This thesis work reports the following structure: In Chapter 1 there will be an introduction on epoxy resins and an exposition of the main problems related to the use of epoxy monomers of petrochemical derivation. It was reported the state of the art on bio-based epoxy monomers, specifically derived from vegetable oils, lignocellulosic compounds and polysaccharides with a focus on furan-based ones; followed by a brief review on bio-based curing agents, specifically carboxylic acids, anhydrides, amino acids and amines. Chapter 2 shows all the materials, the procedures and characterization techniques used. In Chapter 3 are reported synthesis, formulation, characterization and application of the BOMF/MA system. The characterized system has been used as adhesive for carbon fiber composites (CFRP). Thermal, mechanical and adhesive properties of polymerized samples have been evaluated and compared with those of a BPA based system. The results have shown that BOMF/MA resin has outstanding adhesive properties against carbon fiber reinforced composite (CFRP) joints, exceeding the BPA-based counterpart by 3 times. This result is due to the strong hydrogen bonding interaction of the resin with the epoxy substrate CFRP, mediated by the hydroxyl groups formed on the polymerization BOMF/MA. In Chapter 4 the same system has been used as a material for the realization of epoxy nanofibers obtained by electrospinning for the realization of protective layers of membranes in application such as fluid filters. Epoxy nanofibers were obtained by the core-shell method, using PLA as the 'sacrificial polymer'. Chapter 5, will show the realization of a different epoxy system BOMF/IPD. The resin was characterized thermally and mechanically and DSC analysis showed Tg performance at 70 °C, This has allowed to identify the most performant epoxy/curing agent formulation for the realization of conductive nanocomposites by adding suitable quantities of carbon nanotubes (CNT). CNT/epoxy nanocomposites were then used to impregnate a natural cotton fabric, used as thermo-responsive wearable textiles. The temperatures achieved (around 37 °C) demonstrate the high potential for use as wearable textiles and for biomedical devices, being comfortable temperatures for humans. In the last section are summarized the most remarkable results and are depicted the following developments which lead to further improvements of the activities about the investigation of the potential applications of BOMF and different curing agents in green perspective.

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