Stearate-Modified Montmorillonite and Polylactic Acid Synergistically Enhanced the Microcellular of Thermoplastic Polyurethane Elastomer Foam and Improved Its Dimensional Stability

Thermoplastic polyurethane (TPU) elastomer is a commonly used material for foam preparation. However, its application is hindered by significant shrinkage behavior. To reduce the foam shrinkage, polylactic acid (PLA) and calcium stearate-modified montmorillonite (MMT-St) are incorporated into the polyurethane matrix. The TPU/PLA/MMT-St composite foams are formed using an intermittent supercritical carbon-dioxide-foaming process. The addition of PLA inhibits the relaxation of TPU chain segments, while the introduction of calcium stearate (GaSt 2 ) improves the dispersion of MMT within the matrix, increases the nucleation sites of cell growth, and improves cell structure. The cell diameter decreases from 10 to 4 μm, while the cell density increased from 4.1 × 10 12 to 15.8 × 10 12 cell cm −3 . In addition, the cell distribution range narrows from 4–19 to 2–6 μm. Incorporating MMT-St increases the crystallinity and thermal stability of TPU/PLA, mitigates chain relaxation at room temperature, and enhances foam dimensional stability. As a result, this leads to a decrease in shrinkage rate from 27.5% to 5%. As both matrices of the material are thermoplastic, this composite foam possesses recyclability with enhanced material utilization.