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

The morphologies of poly(epsilon -caprolactone) (PCL) blends with hydroxyet hyl cellulose acetate (HECA), a thermotropic liquid crystalline polymer (TL CP), 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 spheruli tes of the PCL/HECA blends show not only the Maltese crosses but also disti nct extinction rings (i.e., a ring-banded spherulitic morphology). The aver age periodic distance of the extinction rings decreases drastically with th e increase of the HECA content from 0.5 to 5 wt % in the mixture, whereas i t decreases only slightly with the further increase of HECA. The periodicit y 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. ( C) 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1681-1686, 2001.