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

Abstract

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(l,4-butylene adipate) (PBA), as well as that of the pure PVF₂ homopolymer. The samples were quenched from 190°C (in the single-phase region for the blend) to 130°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.

Key Words:

• SAXS
• Blends
• Miscibility
• Crystallization
• Dynamics