Peroxide-Driven Morphological Transition of the PHBV Phase in PLA for Transparent, High-Barrier Biodegradable Blends

Developing biodegradable polylactide (PLA) films with simultaneously high gas barrier and optical transparency remains challenging due to intrinsic trade-offs among permeability, crystallinity, and light scattering. Herein, we report a simple, low-cost reactive extrusion strategy that overcomes this limitation by tailoring the morphology of a dispersed poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) phase in a PLA matrix. Trace peroxide addition (0.1 phr) induces an in situ transformation of PHBV from spherical droplets to high-aspect-ratio, platelet-like nanofibers. As a result, the oxygen and water vapor permeability of PLA/PHBV (90/10) films decrease by 94.0% and 80.6%, respectively, while optical transmittance increases from 20.3% to 86.6%. Rheological analysis reveals peroxide-induced viscosity contrast driving phase fibrillation, and positron annihilation lifetime spectroscopy confirms reduced free volume resulting from enhanced interfacial compatibility. This work provides a scalable route for designing multifunctional biodegradable barrier films for sustainable packaging.