Synthesis and characterization of linear and tri-block PLLA-PEG-PLLA blends

This study was conducted to synthesize poly(L-Lactide)–poly(ethylene glycol)–poly(L-Lactide) triblock copolymer (PEGLA) with different PLLA block length, and explore its applicability in a blend with linear PLLA (3051D NatureWorks) with the intention of improving heat-seal and adhesion properties at extrusion coating on paperboard. PLLA-PEG-PLLA was obtained by ring opening polymerization (ROP) of L-lactide using PEG (molecular weight 6000 g mol^-1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy (¹H-NMR). The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology, and differential scanning calorimeter (DSC). All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat PLLA, while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan delta). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.