Crystallization-Induced Nanodomains and Lamellar Organization in Ring-Banded Spherulites of Poly(3-hydroxybutyrate- co -3-hydroxyvalerate)/Poly( p -dioxanone) Blends

While nanodomain segregation is typical in block copolymers, its appearance in blends such as polyhydroxyvalerate/poly(p-dioxanone) (PHBV/PPDO) offers an unusual route to hierarchical ordering. The interplay of composition and crystallization temperature dictates the formation of ring-banded spherulites (RBS). Low PPDO content yields highly regular double-banded structures, whereas higher PPDO levels or elevated temperatures disrupt the periodicity. PPDO incorporation slows crystallization, lowers growth rates, and shifts the optimal window to reduced temperatures. Microscopy shows that PPDO nanodomains are periodically dispersed within PHBV lamellae, generating a crystallization-driven nanophase separation that is essential to the banded morphology. Domain size decreases from ca. ∼400 nm at 70 °C to ca. ∼318 nm at 90 °C, indicating temperature-sensitive confinement. This nanoscale dispersion directly couples the lamellar orientation with phase separation. Structural analysis confirms that higher temperatures shrink domains, thicken PHBV lamellae, and increase the long period. Microbeam SAXS further reveals that dislocation defects in RBS arise from non-uniform lamellar growth, causing localized misalignment and radial offsets, highlighting the sensitivity of banded morphology to local growth variations.