Simultaneously enhancing the melt strength and thermal resistance of PLLA/PVA blends via graft copolymer induced interfacial stereocomplex network

Poly(lactic acid) (PLA) is regarded as one of the most promising biodegradable polymers. However, PLA has inherent limitations, including low crystallinity, low melt strength, and inadequate thermal resistance, which limit its use in blown films and disposable containers. In this study, the poly(vinyl alcohol)-graft-poly(D-lactic acid) (PVA-g-PDLA) graft copolymer was synthesized via the "graft-onto" strategy and incorporated into the poly(vinyl alcohol)/poly(L-lactic acid) (PLLA/PVA) blend. By varying the PVA-g-PDLA content, a physical crosslinked network of stereocomplex crystals was formed, significantly enhancing the blend's crystallization rate, melt strength, and thermal resistance. Compared with the blend without PVA-g-PDLA (PLA7PVA3), the blend PLA7PVA3-g-20 exhibited a 289% increase in crystallization rate at 110 °C, a nearly four orders of magnitude increase in complex viscosity, around 1030% increase in strain-hardening ratio, a 1263% increase in the maximum elongation viscosity, and a 130% increase in Vicat softening temperature. These improvements make PLLA/PVA/PVA-g-PDLA blends promising for applications in blown films, disposable containers, and sustainable packaging solutions.