Preparation of chain-extended poly(lactic acid)/poly(vinyl acetate) composite nanofoams via supercritical CO2 foaming with DFT approach

Biodegradable nanocellular poly(lactic acid) (PLA) foams have emerged as a key alternative to traditional petroleum-based foams due to their environmental friendliness, lightweight properties, and thermal insulation capabilities. In this study, PLA was chain-extended using ethylene-acrylate-glycidyl methacrylate terpolymer as a chain extender, and poly(vinyl acetate) (PVAc) was introduced to prepare CEPLA/PVAc blends. Supercritical carbon dioxide (CO2) was used to prepare nanobimodal cellular foams via a solid-state foaming method. In parallel, density functional theory was employed to quantitatively investigate local CO2 density and associated parameters in the vicinity of various heterogeneous interfaces. Theoretical results indicated that the abundant ester groups in PVAc exhibited high affinity for CO2, leading to higher local CO2 density near these groups, which facilitated the preparation of nanobimodal cellular PLA foams. Foaming experiments indicated that the optimal process conditions for this study were 125 °C and 25 MPa. The CEPLA/PVAc-3.0 foam exhibited the highest volume expansion ratio of 2.03 and displayed a nanobimodal cellular structure comprising large cells (average 796 nm) and small cells (average 270 nm), with corresponding cell densities of 3.3 × 1012 and 7.9 × 1012 cells/cm3, respectively. Moreover, its thermal conductivity reached a minimum value of 0.084 W/(m·K). By combining theoretical simulations with experimental data, the controllable preparation of nanobimodal cellular PLA foams was achieved to a certain extent, thereby improving their foaming and thermal insulation properties. This work provides experimental and theoretical support for the research and development of biodegradable nanocellular foam materials.