Supercritical CO2 Foaming of Thermoplastic Polyurethane Composite: Simultaneous Simulation of Cell Nucleation and Growth Coupling in Situ Visualization

The foaming process of thermoplastic polyurethane (TPU) composites was investigated by the simultaneous simulation of cell nucleation and bubble growth coupling in situ visualization while considering the interaction between multiple bubbles as well as the competitive relationship between cell nucleation and bubble growth. The effect of content and surface properties of rod-shaped fiber, modified magnesium borate whisker (BE-Mg2B2O5), on cell nucleation, and bubble growth was studied, and the mathematical model was established by introducing the contribution factors of rod-shaped fiber for flat and curved surfaces into the classical nucleation theory. It was found that the cell size decreased from 60 to 17 μm and the cell density increased from 106 to 108 cells/cm3 with the fiber content. The cell nucleation rates of TPU composites were positively correlated with fiber content, and their nucleation rates increased from 106 to 109 cells/(cm3·s) compared to pure TPU. The contribution of the fiber's curved surface to cell nucleation gradually enhanced with increasing fiber content. The contribution factor ratio of TPU composites was in the range of the fiber aspect ratio and increased from 5.11 to 9.30. This study provided a theoretical basis for the effect of nucleating agents with different geometries on cell nucleation by regulating the contribution factor ratio of the additives.