Toward Sustainable Poly(lactic acid)/Poly(propylene carbonate) Blend Films with Balanced Mechanical Properties, High Optical Transmittance, and Gas Barrier Performance via Reactive Compatibilization and Biaxial Stretching

Sustainable poly(lactic acid) (PLA)/poly(propylene carbonate) (PPC) blends were compatibilized by the environmentally friendly epoxidized soybean oil (ESO) through the chemical reaction of epoxy functional groups on ESO with the terminated carboxyl and hydroxyl groups of PLA/PPC. The compatibilization effect of ESO was confirmed by Fourier transform infrared spectroscopy, rheological property testing, differential scanning calorimetry, and morphological observations. It was revealed that the molecular chain entanglement between PLA and PPC was significantly enhanced and the dispersed PPC phase size was decreased, which endowed the blend with high viscosity modulus, low tan δ, and great stretchability, especially for the blend containing 1.0 wt % ESO. The compatibilization effect dramatically reinforced the toughening modification of PPC on PLA, resulting in a great ductility with a fracture strain up to 187.3%, more than 20 times that of the pristine PLA, while maintaining a high strength of 44.5 MPa. Compared to the neat PLA and the PLA/PPC blend, the compatibilized blend showed a much larger draw ratio of up to 6.5 × 6.5 during biaxial stretching, producing a uniform film with balanced mechanical properties, high optical transparency, and good oxygen barrier performance. This work will be of vital importance for guiding the preparation of PLA-based films with superior comprehensive properties.