Preparation and characterization of silica aerogel/polytetrafluoroethylene composites

In order to improve their thermal insulation performance, silica aerogel reinforced polytetrafluoroethylene (PTFE) composites with 10–30 wt% silica aerogel were prepared and tested. The morphology, density, structure and thermal properties of the composites were characterized through scanning electron microscopy, infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller analysis, thermo-gravimetric analysis (TGA) and thermal conductivity analysis. A theoretical model of the effective thermal conductivity (ETC) was developed based on the three-level homogenisation theory. It was found that the density of the composites decreases linearly with the mass fractions of silica aerogel. The composites showed remarkable smaller pore radius (1–10 nm) when compared to that of the pure silica aerogel (10–35 nm). The FTIR and TG results confirmed that the reaction of silica aerogel and PTFE occurs during the mixture or heating stage. But the reaction did not effect the structure of the composites. Moreover, the ETC of the composites along the silica aerogel contents can be divided into two stages, where the critical content is 18 wt%. The lowest thermal conductivity can reach 0.13 W m−1·K−1. The ETC of the composites predicted by the theoretical model is in good agreement with those experiment results. The volume fractions of the PTFE in the silica aerogel pore are 87% and 73% for the two stages, respectively, and mainly the large pores on the surface of the silica aerogel particles are filled by PTFE.