Ring-banded spherulites in poly(?-caprolactone) blended with hydroxyethyl cellulose acetate as an indication for partial miscibility

The morphologies of poly(ϵ-caprolactone) (PCL) blends with hydroxyethyl cellulose acetate (HECA), a thermotropic liquid crystalline polymer (TLCP), were investigated by optical microscopy. It is demonstrated that when the pure PCL is crystallized from the melt, a spherulitic morphology arises with distinct Maltese crosses. With the addition of the HECA, the spherulites of the PCL/HECA blends show not only the Maltese crosses but also distinct extinction rings (i.e., a ring-banded spherulitic morphology). The average periodic distance of the extinction rings decreases drastically with the increase of the HECA content from 0.5 to 5 wt % in the mixture, whereas it decreases only slightly with the further increase of HECA. The periodicity of extinction rings is also influenced by the crystallization temperature. The formation of the ring-banded spherulites of PCL in PCL/HECA blends is explained in terms of stress-induced twisted lamellar crystallization and used as an indication of the molecular solubility of the HECA in the PCL. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1681–1686, 2001