Influence of crystallization kinetics on the cellular structure of biodegradable PLA foams during supercritical foaming

Poly (lactic acid) (PLA) foams prepared by supercritical CO 2 foaming offer a sustainable route toward lightweight biodegradable materials, yet their cellular uniformity and mechanical stability are strongly limited by the poorly controlled coupling between crystallization and gas expansion. This study establishes a thermodynamic–kinetic framework to clarify how CO 2 -induced plasticization regulates crystallization kinetics, bubble nucleation, and structural fixation in PLA foams. DSC, SAXS, Avrami kinetic analysis, SEM morphology statistics, and compression testing reveal that dissolved CO 2 lowers the crystallization activation energy from 95.0 ± 2.1 to 82.0 ± 1.6 kJ mo l − 1 , accelerates heterogeneous nucleation, and promotes the formation of finer cellular structures. An optimized crystallinity range of 30–45% was identified, within which the foams exhibited an average cell size below 100 μ m , a cell density of approximately ( 1.84 – 2.24 ) × 10 7 cells c m − 3 , and a foam density of 0.23 – 0.26 g c m − 3 . Within this structural window, crystalline lamellae reinforce cell walls while maintaining sufficient gas expansion, resulting in a compressive modulus of 28–36 MPa and an energy absorption capacity of 2.1–2.6 MJ m −3 . Excessive crystallization, however, causes premature structural freezing and pore inhomogeneity. These results provide quantitative guidance for designing mechanically robust and structurally uniform biodegradable foams through controlled crystallization–foaming synergy.