TEM Observation of Oriented Crystals in Curdlan Tripropionate Fibers and Comparison with Lamellar Crystals in Microbial Polyester Fibers

Abstract

The orientation of fibrillar crystals in curdlan tripropionate (CDTPr) fibers was analyzed by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and compared with that of poly［(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate］ (P(3HB-co-3HV)) fibers. Wide-angle X-ray diffraction pattern of both fibers showed fiber diagram indicating that the crystals were highly oriented along the fiber axial direction. Two clear diffraction points were observed on the meridian in SAXS pattern of P(3HB-co-3HV) fiber, which indicate lamellar crystals aligned with long period. On the other hand, no clear spot reflection was observed for CDTPr fiber and only the streak scattering was observed. TEM observation of the highly ordered structure of CDTPr fibers revealed that fibrillar crystals, 150 nm in length, were highly ordered along the fiber axis, with no clear periodicity along the fiber axis. This highly ordered structure of CDTPr seems to be the reason why no clear SAXS reflection was observed. On the other hand, in the case of P(3HB-co-3HV), lamellar crystals with a thickness of 5 nm were periodically aligned along the fiber axis, with their long axis pointing perpendicular to the fiber axis. The difference in crystal orientation can be attributed to the flexibility of the molecular chains of P(3HB-co-3HV) and CDTPr. P(3HB-co-3HV) have a folded structure in crystals, whereas those of CDTPr have an elongated chain structure in crystals.