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.