Preparación de nuevos nanocomposites multifuncionales de matriz epoxi basados en el empleo de materiales grafénicos

Laburpena

In this PhD Thesis, multifunctional epoxy matrix nanocomposite materials have been prepared and characterized, based on graphene related materials (GRMs). Four types of GRMs have been characterized by three different graphite exfoliation techniques: Liquid Phase Exfoliation (LPE) aiming to obtain two types of graphene with different lateral size; ultra-expansion of an intercalated compound, in this case a Stage I of GIC (graphite intercalation compound), producing a very high lateral size graphene; oxidation-exfoliation-reduction process to obtain a highly reduced graphene oxide. By in situ polymerization, multifunctional nanocomposites have been successfully prepared owning a suitable combination of electrical, thermal and fire resistance properties, due to the incorporation of fire retardant reagents (FRs) and GRMs with synergistic effect. The key points to achieve good results have been the optimization of the dispersion processes at different loads and the composites processing. Regarding GRMs, their presence in the epoxy resin involved structural and functional changes in the polymer as it could be verified through the characterization of the resulting nanocomposites. The crosslinking processes, thermal behaviour, electrical and thermal conductivity and flame retardancy of materials were defined by the chemical nature of the different types of GRMs studied as well as their interaction with the other loads and with the polymer. Among the graphene materials investigated, a multilayer pseudopristine graphene material obtained by intercalating the graphite was the most efficient to achieve a suitable degree of synergy with the CFRs (encapsulated fire retardant). This synergy makes possible to obtain the desired fire resistance, electrical and thermal conductivity using concentrations of 3%, and even lower in some cases. Microencapsulations were studied for the flame retardant reagents aiming to partially reduce the water solubility and to improve the compatibility with the epoxy matrix, as it was proved by microstructural studies with SEM-EDX and the flammability test UL94 V; this improvement was obtained without causing problems in epoxy resin reticulation. Furthermore, the effect of CFRs in flame retardant properties of the epoxy resin implies very low auto-extinguishing times and high fire resistance, revealing a very effective interaction between CFRs and the polymer. The optimum levels of FRs for the composites were achieved for the four epoxy resin studied, using formulation of CFRs with concentrations between 10-17% (% in weight).