Effect of sintering temperature on the crystallization behavior and properties of silica filled PTFE composites

The present study investigated the effect of sintering temperature on the crystallization behavior of polytetrafluoroethylene (PTFE) polymer in SiO₂ filled PTFE (PTFE/SiO₂) composites, as well as the dependences of dielectric properties, thermal conductivity, water absorption and density on the sintering temperature of composites. The composites were sintered by hot pressing at temperatures of 350–390 °C. The melting peaks of the sintered composites were recorded by the differential scanning calorimetry (DSC), and heats of melting were calculated from the peak areas in DSC curves, then the crystallinity of PTFE in composites was deduced. The intensities of the crystal diffraction peak for PTFE were observed by X-ray diffraction analysis. Moisture absorption of the composites was measured conforming to IPC-TM-650 2.6.2. Archimedes’ principle was used to find out the density of the composites. The dielectric constant and loss tangent of the composites were evaluated at microwave frequency region using strip line resonator method according to IPC-TM-650 2.5.5.5 specification. Thermal conductivity was measured by laser thermal conductivity meter. Morphology of PTFE crystals and dispersion of fillers in the PTFE matrix were studied using scanning electron microscopy.