Robust heat resistance and barrier BO-PLLA/PDLA/PPC films by constructing highly dense and oriented stereocomplex crystalline

To simultaneously overcome the low heat resistance and insufficient barrier properties of biaxially oriented polylactic acid (BO-PLA) film, this study concurrently incorporates polypropylene carbonate (PPC) and epoxidized soybean oil (ESO) to regulate the crystalline structure and phase morphology of PLLA/PDLA (LD) mixtures. ESO enhances compatibility between PPC dispersed phase and the LD matrix through reactive compatibilization while also establishing a branched topological molecular structure. This reinforces molecular chain entanglement and increases melt strength of LD-PG blend. During biaxial stretching, PPC and ESO synergistically elevate the alternative folding and stacking of enantiomeric PLA chains, through joint plasticization, enhanced intermolecular interactions, and reinforced entanglement. BO-LD-PG 4 × 4 film achieves a total crystallinity of 47.6% and SC crystallinity of 27.2%. Larger HC lamellas and smaller SC lamellas form highly oriented and interlocked fibrous structures, creating a dense crystalline network with shish-kebab-like crystalline distributed throughout, which significantly improves the heat resistance of BO-LD-PG 4 × 4 film with a shrinkage rate as low as 6.3% at 150 °C. Concurrently, the PPC nanophase and SC/HC crystalline network structure jointly enhance the barrier properties of BO-LD-PG 4 × 4 films, achieving as pH ₂O of 2.96 × 10⁻¹⁴ g · cm/cm² · s · Pa and P O₂ of 1.4 × 10⁻² cm³ · cm/m² · h · 0.1 MPa. This work not only provides an effective strategy for preparing high-performance fully biodegradable packaging materials but also sheds light on the structural evolution mechanisms of LD blends during biaxially stretching.