A synchrotron SAXS study of miscible blends of semicrystalline poly(vinylidene fluoride) and semicrystalline poly(1,4-butylene adipate)

The morphology of a miscible blend of two crystalline polymers (PVF2/PBA) has been investigated by synchrotron small-angle X-ray scattering. Measurements have been made as a function of blend composition and of temperature, probing the morphologies at both the spherulitic and the lamellar levels in both the semicrystalline/semicrystalline and the semicrystalline/amorphous states. The correlation function analysis of SAXS profiles has permitted the determination of characteristic morphological parameters at the lamellar level. For the semicrystalline/amorphous state of the blends containing up to 50 wt % of PEA, the amorphous PEA was (mainly) incorporated between the crystalline PVF2 lamellae, i.e. in the interlamellar region. In the case of semicrystalline/semicrystalline blends, the morphology was more complex. In addition to the pronounced scattering peak from the PVF2 crystalline lamellae, there was a scattering shoulder (or small peak) related to the PEA crystals, indicating that the PVF2 and PEA lamellae were in a segregated arrangement. Taken together, the data led us to the conclusion that PEA could crystallize as a thick lamella in the PVF2 interlamellar region and that there was a mixed amorphous phase on either side of the PEA lamella, i.e, between the PEA and PVF2 crystal lamellae. The proposed structure model for the semicrystalline/semicrystalline PVF2/PBA blends is different from the model proposed by Cheung et al. (Macromolecules 1991, 27, 2520) for semicrystalline/semicrystalline (PCL/PC) blends whereby a random mixture of PC and PCL lamellae exist.