Development of butyl rubber–rutile composites for flexible microwave substrate applications

Butyl rubber–micron rutile (BR/MRT) and butyl rubber–nano rutile (BR/NRT) composites were prepared by sigma mixing. The effect of micron rutile and nano rutile content on dielectric properties at 1 MHz and 5 GHz were investigated. For 0.30 volume fraction (vf) of micron rutile loading, the composites have attained a relative permittivity (εr) of 8.59 and loss tangent (tanδ) of 0.0024 at 5 GHz, and for the same volume fraction of nano rutile content, the composite showed εr of 7.62 and tanδ of 0.0031 at 5 GHz. The thermal properties such as thermal conductivity (TC) and coefficient of thermal expansion (CTE) of both composites were studied as a function of filler loading. It is found that the nano rutile added butyl rubber composites have better thermal properties than those micron composites. The stress–strain curves of both composites show the mechanical flexibility of the composites. The experimental relative permittivity and thermal conductivity of both composites were compared with theoretical models.