Time-resolved X-ray imaging of nanofiller-polyurethane reactive foam systems

A time-resolved X-ray radiography imaging method has been used to in-situ monitor the foaming process of reactive closed cell rigid polyurethane (PU) foam systems filled with nanofillers (nanoclays and nanosilicas). The method enables the visualization of the cellular structure and, by means of image processing techniques, allows determining the modification of expansion kinetics (density evolution) and cellular structure (cell size evolution). A significant increase of cell nucleation has been found for all the nanoparticles under study. In addition, in several cases, foaming kinetics was also modified in presence of nanoparticles, involving a modification of the blowing and/or polymerization chemical reactions. It has been proved that nanoclays morphology and surface modification of nanosilicas have a determining effect on cell size and density evolution during the foaming processes. The obtained results contribute to obtain a better understanding on the polymer-filler interaction and its influence on the foaming processes of PU systems.