Optical birefringence patterns and corresponding lamellar alteration induced by solvent vapor on poly(l -lactic acid) diluted with poly(1,4-butylene adipate)

Cracks appear earlier than crystallization of PBA at ambient temperature. Apparently, the formation of cracks in this blend system is due to thermal shrinkage. Those peaks correspond to the lamellar crystals in the valley region shown by white arrow in AFM images. Peaks in etched sample are more pronounced than that in unetched sample. Peaks in the valley region of unetched samples correspond to the wrinkled lamellae. However, those peaks of etched samples belong to lamellae in circumferential with slanting counterclockwise direction in the valley region. It should be noted here that AFM graph is mirror image of OM graph; thus, counterclockwise slanted lamellae in OM corresponds to clockwise direction in AFM graph. The lamellar pattern of etched samples is also characterized by mainly flat-on lamellae. However, they differ in shape and arrangement in comparison with flat-on lamellae of unetched samples. It may be due to the recrystallization of PBA at ambient temperature after etching process interacts with PLLA in amorphous or crystals states.