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This work compares for the first time the efficacy of using different ionic liquids (ILs) as epoxy hardeners in epoxy-based adhesives. Several phosphonium and imidazolium-based ionic liquids were tested as epoxy hardeners, and the thermal and mechanical properties and the lap shear strength of the cured epoxy resins were studied at different IL concentrations. Both the chemical structure and the concentration of ILs were found to impact the final properties of the epoxy resin, but among the ten different ILs studied, three of them cured the epoxy resin effectively and produced similar and even better mechanical properties and lap shear strength than those obtained with traditional amine-based curing agents. These results constitute an important step towards sustainability thanks to the non-volatility of ILs and the significantly lower amount needed for effectively curing epoxy resins.

Good dispersion of carbon nanotubes (CNTs) together with effective curing were obtained in epoxy/CNT nanocomposites (NCs) using three different ionic liquids (ILs). Compared to conventional amine-cured epoxy systems, lower electrical percolation thresholds were obtained in some of the IL-based epoxy systems. For example, the percolation threshold of the trihexyltetradecylphosphonium dicyanamide (IL-P-DCA)-based system was 0.001 wt.%. The addition of CNTs was not found to have any significant effect on the thermal or low-strain mechanical properties of the nanocomposites, but it did improve their adhesive properties considerably compared to the unfilled systems. This study demonstrates that ILs can be used to successfully replace traditional amine-based curing agents for the production of electrically conductive epoxy/CNT NCs and adhesives, as a similar or better balance of properties was achieved. This represents a step towards greater sustainability given that the vapor pressure of ILs is low, and the amount needed to effectively cure epoxy resins is significantly lower than any of their counterparts.

258 p., El objetivo principal de esta Tesis doctoral es la mejora de la sostenibilidad y propiedades tanto de sistemas termoestables como termoplásticos mediante el empleo de líquidos iónicos. En literatura se reporta la capacidad de los líquidos iónicos de actuar como agentes de curado de resinas epoxi, plastificantes, compatibilizantes de mezclas poliméricas y agentes dispersantes de nanocargas entre otras potenciales aplicaciones. Por ello, en esta Tesis se propone la sustitución de los agentes de curado tradicionales volátiles por líquidos iónicos de baja presión de vapor. Además, se estudian sistemas resina epoxi/PCL, resina epoxi/nanotubos de carbono (CNT) y resina epoxi/PCL/CNT curados con líquidos iónicos para la obtención de materiales con propiedades mejoradas. Por otra parte, también se propone la utilización de líquidos iónicos como compatibilizantes de mezclas PLA/PCL y como agentes dispersantes de CNT en sistemas PLA/CNT y PLA/PCL/CNT.

Epoxy/Polycaprolactone (PCL) blends cured with a conventional diamine (4,4′-diaminodiphenylmethane, DDM) and with different amounts of a disulfide containing diamine (4, 4´-dithioaniline, DSS) were prepared through melting. The curing process was studied by FTIR and differential scanning calorimetry (DSC) and the mechanical behavior of the networks was studied by DMA. The shape memory properties and the recyclability of the materials were also analyzed. All blends showed a very high curing degree and temperature activated shape memory effect, related to the glass transition of the epoxy resin. The PCL plasticized the mixture, allowing tailoring of the epoxy glass transition. In addition, in the blends cured with DSS, as a consequence of the disulfide exchange reaction, the permanent shape could be erased and a new shape could be reprogrammed. Using this strategy, reprogrammable permanent shape memory materials were obtained.