Study on the effect of stretching behavior on the properties of PVDF films and mechanism

Abstract

In this paper, the PVDF film prepared by the traditional casting method has good mechanical properties and breaking strength up to 73.51 MPa. Meanwhile, the crystal structure, thermodynamic behavior, electrochemical behavior and morphological characteristics of the stretched PVDF film are studied based on the molecular level deformation mechanism. The results show that the stretched PVDF film has undergone α→β and γ→β crystal transformation. The parameters of %χc and F(β) in the stretched PVDF film can increase 243.52% and 205.35%, and ΔHm increases 5.06 J/g. However, the melting and decomposition temperatures of stretched film are reduced in different degrees, indicating that stretching makes the thermal stability of PVDF film become worse. The morphological characteristics, electrochemical parameters and CV parameters of PVDF film indicate that the stretched PVDF film have obvious orientation and anisotropy, which generates much more stable self-polarizability. Additionally, based on the experimental results, a new model is proposed to explain the mechanism of stretching effect on PVDF crystal transformation at both macroscopic and microscopic scale, which can reveal the reasons for excellent spontaneous polarization in the stretched PVDF films.