Synthesis of Block Copolymers Through Melt Polymerization for Compatibilizing PLA/PBAT Blends

Abstract

Block copolymers, unlike reactive compatibilizers, can stably localize at the interface without reducing biodegradation rate, making them attractive compatibilizers for PLA/PBAT blends. For industrial use, they should be synthesized from commercial PBAT by melt polymerization to lower costs. However, melt polymerization is exposed to ambient moisture, leading to concurrent formation of PLA homopolymer. In this study, PLA-PBAT block copolymers were synthesized by both solution and melt polymerization with different lactide feed ratios. Melt polymerization was performed in an internal mixer as a precursor to reactive extrusion. Products were characterized by NMR, FT-IR, GPC, DSC, and TGA, and performance in blends was evaluated using DSC, SEM, and UTM. Melt samples displayed two cold crystallization peaks. The high-temperature peak corresponded to PLA homopolymer and became more pronounced with increasing lactide feed ratio. This suggests that excess lactide was consumed in homopolymerization. The presence of PLA homopolymer was more clearly observed in DTA than in GPC. In blends, melt samples improved tensile strength gradually with increasing lactide ratio, whereas solution samples showed the highest strength at a 1:1 PBAT-to-lactide ratio. At the ratio, the blend with solution samples exhibited higher tensile strength than that with melt samples. However, this difference was mitigated when melt samples with higher lactide ratios were incorporated at contents of 5 phr or less. The pristine blend formed metastable alpha ' crystals, while melt-sample-containing blends exhibited both alpha and alpha ' structures, with the alpha form becoming more dominant at higher lactide ratios.