Biaxially Stretched High-Strength Isotropic Poly(ether ether ketone) Films for Low Dielectric Constant Materials

Poly(ether ether ketone) (PEEK) films are widely used in aerospace and telecommunications because of high mechanical strength and insulating properties. However, the mechanical strength and electrical loss of the film in practical applications limit its application; thus, the development of low-cost materials with higher mechanical properties and lower dielectric constants has become the research hot spot. In this work, taking full advantage of the crystalline orientation properties of PEEK films, the construction of isotropic PEEK films was presented by the low-cost biaxial stretching method. The biaxial stretching technique changes the molecular chain arrangement and forms better crystalline structure, which improves the tensile strength and reduces the dielectric constant at the same time. Meanwhile, the macroscopic scale modification and crystalline orientation process of PEEK films under biaxial stretching conditions were investigated as well as the microphase morphology and properties of PEEK films under different stretching ratios (λL), stretching temperatures (T), and stretching speeds (ν). Based on the crystalline and oriented structures, the tensile strength (r-PEEK-4 = 156.7 MPa) of the biaxially stretched PEEK film is nearly 2.5 times higher than the unstretched PEEK film (65.6 MPa), and the storage modulus (2.42 GPa) and Tg (172.3 °C) are also significantly increased. In addition, the dielectric constant of the biaxially stretched PEEK film is drastically reduced to 2.62, and the breakdown strength reaches 503.6 MV/m. The present work has obvious implications for the investigation of the crystalline behavior of PEEK films as well as for applications in the telecommunications industry.