Structure and performance evolution of polybutylene succinate foams with lightweight and high-strength wood-like material under solid-state stretching

Wood possesses a unique structure, characterized by "longitudinal tubular cells and aligned fibers" on its radial section, which current polymer processing techniques find challenging to replicate. In this study, polybutylene succinate (PBS) material, foamed with supercritical carbon dioxide (ScCO₂) at a foaming ratio of 3.56 times, was subjected to forced solid-state stretching. This stretching was conducted above the glass transition temperature (T_g) and below the melting point (T_m), resulting in a transformation of the spherical cells into a "tubular cell" structure. During this process, the polymer material aligned along the height of the tubular cells, undergoing crystalline reordering and growth. Consequently, the tensile strength of the resulting foam material increased significantly from 7.3 MPa to 30.7 MPa, and the tensile modulus rose from 67.3 MPa to 178.8 MPa. Scanning electron microscopy results confirm that the cell structure of the PBS foam transitions from spherical to a regularly arranged tubular configuration. Furthermore, differential scanning calorimetry and small-angle X-ray scattering tests reveal a substantial enhancement in the crystallinity and orientation of the PBS foam cell walls. Complementary static structural simulations conducted in ANSYS Workbench demonstrate that circular cells can indeed transform into a tubular lattice-like structure, akin to that of wood.