The effects of filler content and size on the properties of PTFE/SiO2 composites

A study on PTFE reinforced with SiO2 was described. It included the manufacturing process of SiO2-reinforced PTFE and the effects of the SiO2 content and size on the properties of the composite material, such as thermal, dielectric, tensile strength and morphology, etc. PTFE/SiO2 Composites loaded with two sizes (5 mum or 25 mum SiO2) of filler contents varied from 0-60 wt% were mixed by a high-speed dispersion mixer and made via a two-roll milling machine. Our results showed that the composite filled with 25 mum SiO2 at 60 wt% filler content had the highest modulus, lowest CTEz and acceptable dielectric properties. Composites with different sizes of filler showed a similar trend of decreasing tensile strength and coefficient of thermal expansion (CTEz), and increasing tensile modulus, water absorption and dielectric properties as the filler content increased. Furthermore, the composites filled with small-size filler showed higher water absorption and dielectric loss properties due to the presence of higher SiO2 surface area. Poor adhesion between filler and matrix is a primary cause of low tensile properties and lack of increase in thermal stability. Such phenomenon was also confirmed by fracture surface analysis of scanning electron microscope (SEM). Experimental data were compared with theoretical models from the literatures, which are used to predict the properties of two component mixtures. The results revealed that experimental values of dielectric constant and CTEz agreed with the theoretical calculated values. It was also found that the modified Nicolais-Narkis equation provided a good estimation for the tensile strength of composite.