Biodegradable and Structure-Tunable Poly(lactic acid) Foam Prepared by Temperature-Induced CO₂ Foaming

Abstract

Poly(lactic acid) (PLA) foam has good application prospects in the fields of cushioning, heat insulation, and tissue engineering. However, foaming of PLA is still challenging owing to its crystallization characteristics and low melt strength. In this work, we adopted a temperature-induced CO 2 foaming method to fabricate fully biodegradable and structure-tunable PLA foams. PLA sheets were first soaked in a CO 2 atmosphere at high temperatures (80−120 °C) to achieve a short saturation time and basically amorphous state. Next, PLA sheets were cooled to below 10 °C and CO 2 was decompressed to avoid foaming. Finally, foaming was triggered by heating the CO 2 -rich PLA sheets to 40− 100 °C. As a result, PLA could be foamed similar to amorphous polymers, whose foaming behavior is easily regulated. The fabricated PLA foams with customizable cellular structures had an expansion ratio of 2−10. At low foaming temperatures, the foams exhibited a skin−core cellular structure with large cells near the skin layer and small cells in the core layer. With increasing temperature, the prepared foams had a relatively uniform cellular structure. The prepared PLA foam with the skin−core cellular structure exhibited unique compression properties. During compression, large cells in the skin layer easily deformed to absorb energy, while small cells in the core layer remained unchanged to maintain structural stability.