Crystalline structure, dielectric, and mechanical properties of simultaneously biaxially stretched polyvinylidene fluoride film

Biaxially stretched films have balanced properties in the film plane compared with uniaxially stretched films, thus having wider potential applications. In this paper, the simultaneously biaxial stretching (BO) technology had been applied to poly (vinylidene fluoride) (PVDF) melt extrusion film, and the crystalline structure, dielectric, and mechanical properties of the BOPVDF films were investigated. The results showed that during the simultaneous BO process, the applied stress on the film led to the alignment of PVDF chains into the crystals and the formation of all‐trans planar zigzag (TTT) conformation, thus increasing the relative content of β phase and the crystallinity of BOPVDF films, as well as the dielectric response. When the stretching ratio was 2.0 × 2.0, the dielectric constant of the film reached the maximum, ie, ~12, and the dielectric loss was minimum, ie, ~0.02. At the same time, the mechanical properties of the stretched films were significantly improved and reached the maximum tensile strength with 3.5 × 3.5 draw ratio, ie, 90 MPa.