PBS melt strength improving for supercritical CO₂ foaming molding by physical adsorption and crystallization

The PBS/sepiolite composite materials were prepared using the melt blending, and their processing rheological properties and thermal performance were studied. Taking the example of PBS/sepiolite composite with a 10% sepiolite content, the influence of foaming temperature and CO₂ immersion time on the cellular structure of PBS composite materials was investigated. The experimental results show that sepiolite exhibits good dispersion in PBS, and its addition significantly enhances the crystallization temperature, crystallization rate. The addition of sepiolite increases the viscosity of PBS composite and prolongs the Carreau relaxation time. From the data of extensional viscosity, it can be observed that the addition of sepiolite reduces the extensibility of the melt, but significantly increases the melt strength. When the amount of sepiolite exceeds 10%, the viscosity and crystalline performance of the material are negatively affected by filler aggregation. From the foaming experiment results, it is observed that immersing CO₂ at 106 °C for 90 min achieves the optimal cellular structure. At this point, the foaming expansion ratio can reach 16, the average cell size is 37 μm, and the cell density reaches 4.1 × 10⁷ cells/cm³. Using highly adsorbent sepiolite to enhance the melt strength of PBS for stable foaming is a simple and effective method, avoiding the influence of molecular degradation caused by chemical chain extension or cross-linking.