Unusual Radiating-Stripe Morphology in Nonequimolar Mixtures of Poly(L-lactic acid) with Poly(D-lactic acid)

Extensive microscopic and thermal analyses and X-ray diffraction characterizations are conducted to investigate an unusual morphology and its evolution in extreme nonequimolar mixtures of poly(L-lactic acid)(PLLA) with poly(D-lactic acid) (PDLA) containing a trace amount of stereocomplex crystals. Radiating-stripe spherulites are crystallized on first-grown PLLA/PDLA sc-crystals that act as template substrates for later-grown PLLA. Growth kinetics are analyzed to attempt interpretations on understanding why the unusual PLLA morphology with distinct large radiating dendrites can be packed only in narrow ranges of nonequimolar PLLA/PDLA = 98/2 to 90/10 mixtures and only when crystallized within a suitable T-c range of 125-140 degrees C. Additionally, the interior lamellar assembly for the radiating-stripe PLLA spherulites is dissected to correlate with this unusual morphology with rodlike optical birefringence patterns.