current materials are mostly traditional petroleum-based polymers. [5,6] This will consume petrochemical resources and produce massive hardly degradable waste. [7] Second, toxic organic solvents or flammable foaming agents are widely used in the current preparation processes. [2,3] In addition, the relationship between the foam structure and the oil-adsorption and thermal-insulation performance is still unclear, thus limiting the development of high-performance foams.Poly(lactic acid) (PLA) is one of the biobased and biodegradable polymers with the most potential to replace traditional petroleum-based polymers. [8] Microcellular foaming is a green and safe technology in which supercritical CO 2 or N 2 is used as the physical foaming agent. [9] Therefore, it is an eco-friendly solution to use the microcellular foaming technology to prepare PLA foams for oil-adsorption and thermal-insulation application. Highperformance oil-adsorption materials should have high expansion ratio and open-cell structure, [10] and thermal-insulation materials generally require high expansion ratio and closed-cell structure. [11] However, the preparation of PLA foam with high expansion ratio is still very challenging. [12] The factors affecting the expansion ratio are very complex and can be divided into material structure and process parameters. The material structure mainly includes chain structure, crystalline structure, blend phase structure, etc. [12,13] And the process parameters mainly contain temperature, gas pressure, depressurization rate, etc. [12,14] These factors will affect the gas concentration, polymer viscoelasticity, heterogeneous nucleation, etc.; and then act on the cell nucleation, cell growth and cell stabilization; and finally influence the expansion ratio. [9,12,14] Specially, the PLA is a semi-crystalline polymer with low melt strength and complicated relationship between crystallization and foaming. First, CO 2 can reduce the crystallization and melting temperature of PLA, [9] and change its crystal morphology. [15,16] Meanwhile, crystals in turn can hinder the dissolution of CO 2 in the PLA. [17,18] Second, excessive crystallization will severely limit the cell growth, and ultimately lead to low expansion ratio and non-uniform cell morphology. [17][18][19] Third, the linear PLA generally possesses poor melt strength, which easily leads to cell collapse and gas loss, thereby restricting continuous foam expansion. [12] Fourth, the requirements of high expansion and 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 CO 2 foaming technology without introducin...
