Understanding the effect of particle surface free energy on the structural and mechanical properties of clay-laden rigid polyurethane foams

The surface free energy of nanoclays is shown to be a key parameter in controlling the localization of the particles in the polyurethane matrix, and the structural and mechanical properties of nanoclay laden rigid polyurethane foams. The surface free energy determines the dispersion quality of the nanoclays before foaming, which in turn determines the available surface area for heterogeneous nucleation during foaming. It has been found that particles showing the best dispersion quality do not necessarily lead to the best mechanical properties of the foams. On the contrary, the nanoclays which are likely to get trapped at the polyurethane-air interface during foaming, yield improved mechanical properties as compared to the neat polyurethane foam, despite their less favorable dispersion. The interfacial adsorption stabilizes the cell wall during cell growth, leading to smaller cells after rigidification, as compared to the nonadsorbing nanoclays. (C) 2014 Elsevier Ltd. All rights reserved.