Preparation of high-expansion open-cell polylactic acid foam with superior oil-water separation performance

Environmentally friendly and non-toxic polylactic acid (PLA) foam has shown great application prospects in heat preservation, adsorption and other fields. However, it is still challenging to prepare high-expansion PLA foam. Herein, a cooling batch foaming process under supercritical CO₂ (sc-CO₂), based on pre-melted non-crystalline state, was proposed to prepare PLA foams with high expansion ratio. The CO₂ dissolved in the polymer melt will lower the crystallization temperature of PLA. Due to the lack of crystallization, the foaming temperature of PLA can be reduced, which increases the CO₂ saturation and helps foam. When foaming is triggered before crystallization, ultrahigh expansion foam can be produced. Based on pre-melting treatment, the maximum expansion ratio of PLA has reached 59.7-fold. At the same time, an open-pore structure is produced by this method, which can selectively absorb oil from water. In addition, the adsorption capacity of CCl₄ reaches 15 g/g, and there is no significant attenuation in 20 adsorption-desorption cycles. This work provides a green, solvent-free method to prepare biodegradable oil-adsorbing foam.