Rigid polyurethane (RPU) foams are the main thermal insulating materials, since they can be used simultaneously as structural materials, due to a unique combination of low weight, low thermal conductivity and good mechanical properties . Moreover, it is well known that the thermal and mechanical response of RPU foams can be enhanced by the incorporation of diverse fillers into the PU matrix, in particular nanoparticles [2-7]. In most of the studies, dispersing nanoparticles in one of the RPU components is not a simple task that requires specific dispersion methods and/or special surface treatments to reach a certain degree of dispersion. Moreover, the nanoparticles addition into PU foams may also modify the reaction kinetics, what would give rise to unexpected consequences on the cellular structure and on the final properties since some properties may be improved, but others may be worsened.
Herein, we present some strategies to solve the problems mentioned for RPU foams nanocomposites. In the first part of this study, we describe the synthesis of water-blown RPU foams from polyols functionalized with low amounts of graphene oxide (GO) (0.017, 0.033 and 0.083 wt%) . The influence of GO on the cellular structure, thermal conductivity (TC), and mechanical properties of the RPU foams is studied. Moreover, a kinetic study is carried out by infrared expandometry , FTIR spectroscopy and temperature measurements to evaluate the effect of GO on the foam formation. One of the main advantages of this approach is that GO is chemically incorporated into polyol chains, what precludes the nanofiller agglomeration and avoids the dispersion problem previously mentioned. The results of this part showed that 0.033 wt%GO is the optimum content in the final foam, which shows a cell size decrease, and consequently a TC reduction in comparison with the pure material. However, the mechanical properties are not improved and the reaction kinetic is modified by the presence of GO. In the second part of this study, based on the information collected from the kinetic study, we have optimized the system containing 0.033 wt%GO to improve its mechanical properties. For this purpose, a series of RPU foams are synthesized by varying the isocyanate index, the amount of catalyst and the amount of surfactant. The results show how, by controlling PU formulation, both the thermal and the mechanical behaviour are improved for RPU foams functionalized with 0.033 wt%GO.