Morphology of poly( l-lactide) solution-grown crystals

Abstract

Solution-grown crystals (SGC) of poly( l-lactide) (PLLA) were prepared from 0.01 % (w/w) or 0.08% (w/w) acetonitrile solution by an isothermal crystallization method. Their morphology and structural features were examined by transmission electron microscope with the diffraction mode, wide-angle X-ray diffractometry and atomic force microscope. The molecular chains are packed in the manner perpendicular to the basal plane of the well-defined, lozenged, thin SGC with developed spiral dislocation growths; highly-ordered electron diffraction patterns produced by the crystal provided the orthorhombic unit cell parameters: a = 1.078 nm, b = 0.604 nm, c(fibre axis) = 2.87 run. This unit cell of the PLLA SGC contains 20 monomeric units in terms of density measurements. On the basis of the crystal characteristics of SGC, we propose that the two molecular chains locate at the centre and also at each corner of the unit cell. The annealing effects of SGC were studied in parallel to indicate the existence of surface roughening and lamella thickening, depending on the annealing conditions.