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ABSTRACT:The morphologies of poly(⑀-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.

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Polarized light microscopy was used to investigate the presence of preferred molecular orientation in the LCP phase of PPS/LCP blends after injection moulding. Normal birefringence effects appeared to be complicated by artifacts due to sample preparation and by the complex nature of polarized light transmission through a multicomponent sample. It was found, however, that, during low-temperature cutting of optically transparent thin sections on a standard microtome, individual LCP particles could be separated from the PPS matrix, and their birefringence analyzed separately. Preferred orientation was detected only in LCP fibrils which dominated in skin regions, but not in droplet-shaped particles which had formed in core regions. Quantitative measurements indicated that the molecular orientation of the fibrils increased linearly with their length-to-diameter aspect ratios which ranged from 15 to 50. Even for the highest aspect ratios, however, the degree of orientation was always less than that which could easily be introduced into pure LCP thin-film samples by manual shearing