Natural Rubber Composites Containing Fillers of Sol–gel Glasses and Glass–ceramics in the CaO–SiO 2 –P 2 O 5 System

A number of properties of natural rubber-based composites containing fillers of sol–gel glasses and ceramics from the CaO–SiO 2 –P 2 O 5 system were investigated and compared. Its goals were to evaluate and select more suitable usages in flexible electronics, in particular as substrates and insulating layers in antennas for wireless communications. The fillers were characterized by XRD, SEM, adsorption–texture characteristics and particle size distribution. The composites were characterized by their vulcanization, physico-mechanical, dielectric and dynamic characteristics, as well as their volume resistivity and coefficient of thermal conductivity. The studies revealed that the specific features of the fillers, above all their texture characteristics (specific surface area, presence and amount of micro- and mesopores) have a significant impact upon all studied properties of the composites. The complex evaluation has demonstrated that the composites containing glass–ceramic fillers, especially at 20–50 phr, are more suitable as substrates and insulating layers in flexible antennas for wireless communications.