Structure and morphology of biodegradable PBAT/thermoplastic starch blends compatibilized with carboxylated liquid polyisoprene

Insufficient compatibility between hydrophilic thermoplastic starch (TPS) and hydrophobic poly(butylene adipate-co-terephthalate) (PBAT) results in poor interfacial adhesion and phase separation, which limit the performance of their blends. Addressing this issue is essential for developing high-performance biodegradable materials suitable for large-scale packaging applications. In this study, a compatibilization strategy based on carboxylated liquid polyisoprene (LIR-410) as a compatibilizer and dicumyl peroxide (DCP) as a reactive agent was applied to PBAT/TPS blends. TPS was first modified with LIR-410 via hydrogen bonding between hydroxyl groups of starch and carboxyl groups of LIR-410. In the second step, thermal decomposition of DCP initiated covalent coupling involving the double bonds of LIR-410 and the PBAT backbone. The non-compatibilized PBAT/TPS blend was used as a reference to evaluate the effects of TPS modification and reactive compatibilization. Structural characteristics, molecular morphology, and segmental mobility of the blends after five months of storage were investigated using solid-state 1 H and 13 C NMR spectroscopy, dynamic mechanical analysis (DMA), and X-ray diffraction (XRD). NMR analyses revealed hydrogen-bonding interactions among glycerol, the compatibilizer, and starch, reducing glycerol phase separation and starch recrystallization in the blend compatibilized solely with LIR-410. DMA indicated partial incorporation of LIR-410 into the TPS phase in this blend. On the other hand, reactive blending with DCP promoted finer dispersion of TPS within the PBAT matrix and predominantly influenced the blend morphology. Improved interfacial interactions between the polymer phases were confirmed by DMA and proton spin-lattice relaxation times in the rotating frame, which indicated reduced dynamic heterogeneity of PBAT segmental motion after compatibilization. The synergistic effect of liquid polyisoprene and dicumyl peroxide was thus demonstrated to be an effective compatibilization strategy for PBAT/TPS blends, highlighting their potential for applications in sustainable packaging and agricultural films.