Preparation of hollow TiO2 nanospheres with highly porous surface for effective nucleating agents in supercritical carbon dioxide foaming of thermoplastic polyurethanes

In this study, hollow nanospheres of titanium dioxide (TiO₂) are prepared and utilized as potential nucleating agents in supercritical carbon dioxide (scCO₂) foaming process of thermoplastic polyurethanes (TPUs) at different foaming temperatures and saturation pressures. To produce the hollow nanospheres of titanium dioxide (TiO₂), well-defined spheres of polystyrene (PS) with a diameter of about 300 nm are first synthesized as templates using surfactant-free emulsion polymerization. A layer of titanium tetraisopropoxide (TTIP) is then uniformly coated on the PS spheres followed by calcination in a furnace to convert the titania layer to the titanium oxide layer. Hollow nanospheres of titanium dioxide with a well-defined morphology are prepared by calcination at high temperatures, as the PS spheres completely decompose. Interestingly, highly porous structures, which give rise to high surface area for trapping scCO₂, are generated on the surface of the TiO₂ nanoparticles during the thermal treatment. The dispersion of TiO₂ nanospheres in the TPU matrix is successful, serving as heterogeneous nucleating agents that influence the cell density and morphology of the extended TPU in the foaming process.

Graphical abstract

In this study, hollow nanospheres of titanium dioxide (TiO₂) with unique porous surface are prepared and utilized as potential nucleating agents in supercritical carbon dioxide (scCO₂) foaming process of thermoplastic polyurethanes (TPUs) to control various foaming parameters including foaming ratio, cell size, cell density etc.