Nanocomposites de Poliuretanos Elastoméricos y Nanotubos de Carbono Multipared

Resumen

A kinetic analysis of the reactive system was performed in order to adjust the optimum temperature and time parameters for the systematic synthesis of the segmented polyurethanes by the two shot polymerisation approach. In conclusion of this first study the aliphatic HDI resulted to have lower kinetic constants than systems based on aromatic diisocyanates found in literature. In addition the reaction mechanism is believed to vary from them attending to the different global reaction order found for this system of n + m ¿ 2, as comparison with those reported which approach n + m ¿ 3. The nano/microstructure of the resulting series of polyurethanes were analysed and compared to a series of polyurethanes in which the HDI was substituted by the aromatic 4,4'-diphenylmethylen diisocynate (MDI). Notable differences in nano/microphase separation were found and those were also related with the macroscopic properties differences these two set of polyurethanes presented. Multiwalled carbon nanotubes were functionalised with different organic groups onto their surface in order to study the effect of the preferential hierarchical nanostructuration of the nanotubes within the different polyurethane phases onto the mechanical performance of the resulting nanocomposites. Nanocomposites with those nanotubes were prepared by the solvent casting method. Functionalisation of nanotubes with polyurethanes hard segments resulted to improve ductility but with a concomitant reduction of tensile strengths, as in comparison with acid treated nanotubes. The not so important improvement of mechanical performance could be related to the relative big sizes that nanotubes have in comparison to polyurethanes hard domains, being, as demonstrated by other groups, important to target polyurethanes hard domains in order to obtain improvement on mechanical properties without a consequent reduction in ductility and toughness, therefore resembling the performance of materials such as natural silk. The effect of polyurethane hard segment content in the final nanocomposites was analysed. According to the results a preferential interaction of nanotubes with polyurethanes hard segments can be assumed although nanotubes introduction hindered both soft and hard segments crystallisation. In all cases carbon nanotubes percolative network formation seemed to be crucial for obtaining significant reinforcement, being observed at this stage, a reduction of ductility. Polyurethane hard domains nature has been demonstrated to have important effect on nanotubes reinforcing character. Buckypaper infiltration approach was employed to produce medium and high nanotube loading nanocomposites obtaining stiffer, lighter and more electrically conductive nanocomposites than with the solvent casting approach. Differetn applications fields, such as tissue engineering, strain and chemical sensing, smart textile or in future materials for space exploration, are proposed and discussed for the system resulting for the system resulting from the combination of polyurethanes and carbon nanotubes in different manners.