Phase Evolution and Selective Barium Titanate Localization in Poly(vinylidene fluoride) and Epoxidized Natural Rubber Blends with Tunable Mechanical and Dielectric Properties

Non-vulcanized blends of poly(vinylidene fluoride) (PVDF) with epoxidized natural rubber containing 50 mol% epoxide (ENR-50) in 80/20–20/80 wt% ratios were prepared by melt blending. The PVDF/ENR-50 blends at 80/20 and 50/50 were filled with 5 vol% barium titanate (BT). SEM analysis revealed a change in morphology from PVDF continuity to apparent co-continuity at 60/40–50/50, followed by ENR-50 continuity at higher ENR-50 content. Increasing the ENR-50 content reduced stiffness and tensile stress but increased extensibility, with elongation at break values of about 1000–2200% in the ENR-50-rich blends. Furthermore, the PVDF crystallization temperature increased from 135.8°C in neat PVDF to 139.3°C at the 50/50 composition, whereas normalized PVDF crystallinity decreased from 54.2% at 60/40 to 43.7% at 20/80 due to phase confinement. Relaxation peaks at − 36 and − 9°C indicated phase separation with partial interface compatibility. The novelty lies in the identification of two-phase inversion boundaries and the correlation between phase continuity and mechanical, thermal, dynamic-mechanical, and dielectric behavior. Moreover, BT particles preferentially segregated to ENR-50, increasing the average size of ENR-50 domains in the 80/20 blend from 6.5 to 11.4 µm without altering PVDF continuity.