Controlling foamability plays the central role in preparing PLA foams with high performances. To achieve this, chain extension was often used to improve the rheological property of PLA resins; however, despite the availability of this approach, it often deteriorates the biodegradability of PLA and greatly increases the processing cost and complexity. Hence, we reported a special crystallization induction method to design PLA foams with a tunable cellular structure and a high expansion ratio. A novel crystallization-promoting agent combination (D-sorbitol, CO₂, and phenylphosphonic acid zinc salt) was used to induce PLA to enhance the chain interaction force and chain mobility and to provide crystallization templets. A series of PLAs with tunable stereocomplex (Sc)/α crystallinity and rapid non-isothermal crystallization ability were obtained. The effect of various crystallization properties on the foaming behavior of PLA was studied. The results demonstrated that proper crystallization conditions (a small spherulite size, a crystallinity of 6%, and rapid crystallization ability) could virtually contribute to the optimized cellular structure with the highest cell density of 4.36 × 10⁶ cell/cm³. When the Sc crystallinity was above 10%, PLA had a superior foamability, which thereby resulted in a high foaming expansion ratio of 16.2. A variety of cellular morphologies of PLA foams could be obtained by changing the foaming temperature and the crystallization property. The proposed crystallization-induced approach provided a useful method for controlling the cellular structure and the performances of the PLA foams.

The effect of a bio-based macromolecule, poly(butylene adipate-co-terephthalate) (PBAT), on the crystallization and foaming behavior of poly(lactic acid) (PLA) was evaluated. The crystallization kinetics results show that the addition of PBAT improved the crystallization of PLA by increasing the overall crystallinity and enhancing the crystal morphology of PLA. The massive crystallization zones may have prevented the escape of foaming gases to the surrounding area; the expansion ratio of the PLA foams increased from 4.87 to 10.94. Thus, a novel macromolecular crystallization nucleating agent for PLA was developed; the effect of the crystallization of PLA on its foaming behavior was also investigated. A high expansion ratio and finer cellular structure of PLA foam were obtained by optimizing the PBAT content.