Effect of PPC Content on the Structure and Properties of PBAT/PLA/PPC Ternary Composite Mulch Films

The binary blend of poly(butylene adipate-co-terephthalate) (PBAT) and poly(lactic acid) (PLA) has emerged as the primary base material combination for biodegradable mulch films because of their favorable processability and biodegradability, offering a viable route to replace conventional polyethylene films in agricultural applications. However, the PBAT/PLA binary system suffers from thermodynamic incompatibility, limiting simultaneous achievement of mechanical, barrier, and optical properties. This study introduces poly(propylene carbonate) (PPC) as the third component and investigates its content (0-20%) on the microstructure and performance of PBAT/PLA/PPC ternary films. At PPC ≤ 10%, the system maintains an amorphous homogeneous structure, and PPC enriches the surface and improves interfacial adhesion. When the PPC content is 10%, the blend exhibited a transverse tensile strength of 43.3 MPa, an elongation at break of 338%, and a 29.8% reduction in water vapor permeability versus the neat blend. At 15% PPC, the compatibility threshold is exceeded, causing severe phase separation, a sharp drop in melt strength, and deteriorated mechanics. At 20%, phase separation induces PBAT/PLA crystallization, further enhancing barrier performance but reducing thermal stability and transparency. Differential scanning calorimetry and dynamic rheological analysis confirm the compatibility threshold, while X-ray photoelectron spectroscopy, X-ray diffraction, and scanning electron microscopy reveal abrupt changes in surface chemistry, crystal structure, and morphology. Overall, 10% PPC offers the best balanced properties. This work elucidates structure and property relationships, providing a basis for the rational formulation design of biodegradable mulch film. Further field weathering and biodegradation tests are required to validate their practical agricultural performance.