Fluorimetric visualization of the dispersal of polyethylene terephthalate (PET) filler in polyurethane foams

The use of organic fillers such as recycled polyethylene terephthalate (PET) represents an interesting environmentally friendly alternative for reducing the costs of production of flexible polyurethane foams. By using an appropriate siloxane-based SiOC surfactant rather than a conventional SiC surfactant, flexible polyurethane foams containing significant quantities of micronized recycled PET filler can be prepared without compromising the relevant physical properties required of mattress-quality polyurethane foams by ABNT standards, such as density, resilience, comfort and fatigue. In the present work, it is demonstrated that, by employing micronized PET fluorescently labelled with a fluorescein chromophore, the three-dimensional distribution of the PET filler throughout the foam block can be visualized. Differences in the distribution of the fluorescent PET are found in foams produced with a conventional SiC surfactant compared to those produced with the SiOC surfactant, consistent with the differences in physical properties of the foams. Finally, examination of the cellular structure of the foam points to predominant localization of the fluorescence in the tetrahedral Plateau borders of the foam in the resultant PET-containing polyurethane foams due to the heat generated by the polymerization reaction and the capillary and/or Marangoni flows that accompany the expansion and thinning of the foam cells during the polymerization.