Polyurethane nanocomposite foams: Correlation between nanofillers, porous morphology, and structural and functional properties

Polyurethane-based foams have found widespread use in different branches of industry. By modulating the formulation of polyurethane precursors, such as polyols and isocyanate, it is possible to obtain open-cell flexible foams and closed-cell rigid foams, to be used in a wide range of applications. The properties of polyurethane foams do not depend only on the intrinsic properties of the polymer, but also on the foam morphology such as cell density, cell size, and size distribution. However, polyurethane foams suffer from low mechanical strength, poor surface quality, low thermal and dimensional stability, and fire resistance, thus limiting their use in several fields of application. To overcome these limits, a possible strategy is the use of nanofillers to obtain polyurethane nanocomposites. Particularly interesting are those nanofillers which, acting as heterogeneous nucleation sites, are able to decrease cell size and at the same time reinforce the polyurethane matrix. In this review chapter, it has been shown that, due to the larger surface area of nanofillers and to the possibility to chemically functionalize their surface, it is possible to obtain polyurethane nanocomposite foams which combine the advantages of polyurethane foams such as wide range of densities, low thermal conductivity, and good sound absorption with unique properties of nanocomposites such as enhanced thermal stability, fire resistance, and mechanical properties. Finally, results proposed in the recent literature show that, due to an enhanced filler/ PU matrix interaction and a higher filler efficiency, the synergistic use of various nanosized particles can be considered as a valuable approach for the development of multifunctional polyurethane foams which may have a tremendous impact in several application fields with respect to traditional materials.