Integrating Hollow Metal‐Organic Frameworks with Supercritical CO₂: A Path to High‐Performance Polystyrene Microcellular Foams

Polymer foams, particularly those prepared using supercritical carbon dioxide (Sc‐CO 2 ), are extensively utilized in diverse applications like thermal insulation and packaging due to their lightweight and efficient properties. However, the effectiveness of Sc‐CO 2 foaming is often limited by low cell density and large cell size, mainly resulting from insufficient nucleation control and inadequate gas management. In this study, hollow metal‐organic frameworks (MOFs) (HZIF‐8) were introduced as effective nucleating agents in Sc‐CO 2 ‐assisted polystyrene (PS) foaming. Owing to their unique hollow structure and high internal surface area, HZIF‐8 significantly enhances gas adsorption and storage capacity, thereby improving nucleation efficiency during the foaming process. The results show that incorporating HZIF‐8 into PS significantly increases the cell density (up to 1.4 × 10 9 cells cm −3 ) and decreases the average cell size (to 8.6 μm) under optimal foaming conditions (13.8 MPa, 100 °C). Compared to conventional ZIF‐8 nanoparticles, the hollow structure of HZIF‐8 facilitates more efficient CO 2 uptake, leading to a finer microcellular morphology, more stable foam expansion, and enhanced mechanical properties. These results demonstrate the potential of hollow MOFs in creating high‐performance microcellular foams, with promising applications in energy‐efficient insulation, lightweight packaging, and functional materials.