Morphological changes in poly(L-lactide)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends induced by different miscibility

The poly(L-lactide) (PLLA)/poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) crystalline/crystalline blends with different miscibility were prepared by varying the molecular weight of the PLLA component. The relationship between miscibility and spherulitic morphology were studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and atomic force microscopy (AFM) in this work. Penetration of PHBV spherulites into the pre-existing PLLA spherulites was found at intermediate and higher temperature in both the miscible PLLA25/PHBV blend and the partially miscible PLLA150/PHBV blend. However, the penetration of PLLA crystals into the spherulites of PHBV was only found in PLLA25/PHBV blend during the cold crystallization and simultaneous isothermal crystallization, because there were not enough uncrystallized PLLA150 inside the lamellae of PHBV for the PLLA150/PHBV blend. The formation of interpenetrating spherulites was analyzed on the basis of birefringence. In the case of immiscible PLLA1800/PHBV blend, the morphology results under any crystallization condition imply that the spherulites of one component have no influence on the crystallization of the other one. It is concluded that the miscibility of the two components plays an important role in determining the morphologies of polymer blends. (C) 2015 Elsevier Ltd. All rights reserved.