Structural study of poly(L-lactic acid) spherulites.
Spherulites of poly(L-lactic acid) (PLLA) and of its blends with atactic poly(3-hydroxybutyrate) (a-PHB, from 10 to 75 wt %) were investigated by microfocus X-ray diffraction using synchrotron radiation. Radial scans in 5 microm steps with 3 microm beam diameter were performed. In PLLA, tens of identical diffraction images were collected. The unit cell a-axis was radially oriented, and the other axes lacked any specific orientation. In contrast, all PLLA/a-PHB blends showed a periodic change of diffraction pattern with increasing distance from the spherulite center. In all cases, the a-axis lay along the radius, while the b- and c-axes rotated about a with a defined periodicity. The unit cell twisting frequency increased with a-PHB content and closely matched the band spacing observed by polarized optical microscopy, which changed from 250 to 60 microm when the amount of a-PHB increased from 10 to 75 wt %. Concomitantly, a gradual broadening of all X-ray reflections was observed.
Department of Chemistry G Ciamician and ISOF CNR, University of Bologna, via Selmi 2, 40126 Bologna, Italy.
Massimo
M
Gazzano
Maria Letizia
ML
Focarete
Christian
C
Riekel
Mariastella
M
Scandola
D003460:Crystallization; D018360:Crystallography, X-Ray; D004337:Drug Carriers; D019344:Lactic Acid / Q000737:chemistry*; D011091:Polyesters; D011108:Polymers / Q000737:chemistry*; D017356:Synchrotrons
D004337:Drug Carriers; D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide)