A time-resolved synchrotron SAXS study of crystallization in a miscible blend of poly(vinylidenefluoride) and poly(1,4-butylene adipate)

Time-resolved small-angle x-ray scattering (SAXS) has been used to probe the crystallization dynamics of poly(vinylidenefluoride) (PVF2) in its miscible blend with 30 wt% poly(1,4-butylene adipate) (PBA), as well as that of the pure PVF2 homopolymer. The samples were quenched from 190 degrees C (in the single-phase region for the blend) to 130 degrees C to crystallize the PVF2. The results show that the isothermal crystallization rate of PVF2 in the blend is slightly faster than that of the pure PVF2 homopolymer. Based on the time variation of the invariant, the faster crystallization rate of the blend could be due to a faster growth of the PVF2 lamellar stacks in the blend. The blend has a lower glass transition temperature than that of the homopolymer, hence the PVF2, component in the blend has a higher mobility, which may result in a faster growth of the PVF2 lamellar stacks. During the primary crystallization process, the pure PVF2 homopolymer shows a decrease in the average thickness of the PVF2 crystalline lamellae, suggesting a progressive insertion of thinner PVF2, crystalline lamellae, but an approximately constant long period implies an increase in the average thickness of the interlamellar amorphous region. This increase suggests that the thinner PVF2 crystalline lamellae insertion could occur in the free space left between the existing lamellar stacks, rather than within the existing lamellar stacks. On the other hand, the blend shows a constant average thickness of the PVF2, crystalline lamellae and a constant long period, suggesting that the insertion (if it exits) of PVF2, crystalline lamellae should also be in the free space left between the existing lamellar stacks.