Polyurethane foam-clay nanocomposites: nanoclays as cell openers

Abstract

Flexible and rigid polyurethane (PU) foam nanocomposites were synthesized using unmodified and organically modified montmorillonite clays. X-ray diffraction and transmission electron microscopy studies showed that, while the unmodified clays were intercalated, the modified clays were exfoliated in the foams produced. The cell morphology of the foams was investigated by environmental scanning electron microscopy. The fraction of open cells (defined as the cells in which the foam lamellae are all ruptured) in the foam is an important parameter governing many properties, such as the degree of softness in the case of flexible foams and dimensional stability for both rigid and flexible foams. The open cell content in PU-clay foamed nanocomposites was investigated. It was found that clays act as efficient cell openers in both rigid and flexible foams and a greater fraction of open cells was obtained with increasing clay concentration. Modified clays were found to be more efficient cell openers than the unmodified clay. The degree of softness of flexible foam was increased and the dimensional stability of both rigid and flexible foams was improved, with clay addition. The thermal conductivity and compressive strength of the rigid foams were not significantly affected by clay addition. The kinetics of the foaming process with different clays was investigated. The polymerization and the foaming reactions were found to be affected in different ways for the modified and unmodified clays. Comparison with chemical cell openers in the case of flexible foams indicated that clays could be a good alternative.