Oppositely synchronized lamellar bending in poly(L-lactic acid) versus poly(D-lactic acid) blended with poly(1,4-butylene adipate)

Lamellar bending habits, as influenced by molecular-chain chirality, in packing into dendritic spherulites with specific optical patterns are discussed using two model polymers of opposite chirality that are blended with a common polymer as examples: i) poly(l-lactic acid)/poly(butylene adipate) (PLLA/PBA) and ii) poly(d-lactic acid)/PBA (PDLA/PBA) blends. The bending habits in the spherulites of PLLA or PDLA blended with PBA are dictated by the chirality, specifically the counterclockwise and clockwise directions for the PLLA/PBA (50:50) and PDLA/PBA (50:50) blends, respectively. Straight lamellae in spiral lozenge crystals are packed with crystal aggregates of PLLA on top of the flat-on lamellae plates acting as a basal plane during crystallization at T _c; spiral lozenge-crystal frameworks are surrounded by needle-like crystals resembling PBA crystals.