Effects of surface fluoride-functionalizing of glass fiber on the properties of PTFE/glass fiber microwave composites

Abstract

In this work, fluoride-functionalized glass fiber (F-GF) was prepared, in which glass fiber (GF) was modified with γ-methacryloxy propyltrimethoxy silane (γ-MPS), and then reacted with 2,2,2-trifluoroethyl methacrylate (TFEMA). Subsequently, PTFE/glass fiber microwave composites were prepared by incorporating 5 wt% of the GF, γ-MPS modified GF (M-GF) or F-GF into PTFE. The effect of F-GF on the mechanical and dielectric properties, as well as moisture absorption and coefficient of thermal expansion of the composites were investigated. The results show that fluorine is successfully grafted onto the surface of GF through –CF₃ group, and F-GF forms a dense and compact interfacial structure with PTFE. The mechanical properties of PTFE/F-GF, including tensile strength (38.53 MPa) and elongation (226.82%), are obviously higher than those of PTFE/M-GF (34.73 MPa and 179.50%, respectively) and PTFE/GF (34.82 MPa and 174.33%, respectively). In addition, the PTFE/F-GF composite shows improved density (2.174 g cm⁻³), dielectric constant (2.18), and decreased dielectric loss (0.0009), moisture absorption (0.008%) and temperature coefficient of dielectric constant (−18.6 ppm per °C). The conclusions demonstrate that the method of surface fluorination of glass fibers offers promising application in PTFE based microwave materials.