Super High‐Expansion Poly(Lactic Acid) Foams with Excellent Oil‐Adsorption and Thermal‐Insulation Properties Fabricated by Supercritical CO₂ Foaming

Abstract Bio‐based and biodegradable poly(lactic acid) (PLA) foams with a high expansion ratio show great application potential in oil‐adsorption and thermal‐insulation, which are crucial for oil‐spill cleanup and energy saving. However, it is difficult to prepare high‐expansion PLA foam due to the poor melt strength and complex crystallization behavior of PLA. Herein, super high‐expansion PLA foams with excellent oil‐adsorption and thermal‐insulation properties are successfully prepared using a modified supercritical CO₂ foaming technology without introducing eco‐unfriendly chain extenders or fillers. High‐strength melt at low temperature and low‐strength melt at high temperature are used to prepare closed‐cell and open‐cell foams, respectively. The resulting PLA closed‐cell foam with an expansion ratio of 60 shows a thermal conductivity as low as 31.7 mW m⁻¹ k⁻¹, and the PLA open‐cell foam with an expansion ratio of 43 and exhibits an adsorption capacity of 10.9–31.2 g g⁻¹ for various oils. Based on the prepared PLA foams with tunable structure, the influence of cell structure on the properties of the foam is also studied. Of particular note, reducing the cell size can obviously enhance the surface hydrophobicity of PLA foam. This work provides a green strategy for the preparation of eco‐friendly materials applied in environment protection and energy conservation.