The morphology and microstructure of crystalline blends of poly (ethylene glycol) (PEG) and poly (L-lactic acid) (PLLA) were examined using polarized optical microscopy (POM) and scanning electron microscopy (SEM). As PEG was in the melt state during PLLA crystallization, it was rejected from the PLLA bundles. The size of PEG inclusions determined by their extraction is around 1 μm. The PEG/PLLA blends exhibited not only spherulites with Maltese crosses but also distinct extinction rings. The formation of ring-banded spherulites and the periodic distance between the rings were related to the degree of supercooling of the polymer. The ring-banded structure was easily obtained at a high PEG content (70 wt%) and high PLLA crystallization temperature (120 °C). The end group of PEG significantly affected the morphology of PEG/PLLA blends. PLLA blended with PEG containing both end groups as CH3 exhibited the greatest melting temperature depression and lowest degree of supercooling of PLLA, implying the formation of ring-banded spherulites with the smallest PEG content (30 wt%) and lowest PLLA crystallization temperature (85 °C). PEG morphology was also observed using POM after the formation of PLLA crystals. Because PLLA crystals confined the formation of PEG crystals, the chain growth direction of PEG was in association with that of PLLA. Therefore, a brighter POM image was obtained on PEG crystallization.
