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

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.