Changes in Dielectric and Mechanical Properties of Silicone Rubber Caused by Silicone Grease Absorption

Abstract

Silicone rubber (SR) is widely used as insulation for cable accessories and silicone grease severs as a lubricant during its installation. However, the absorption of silicone grease during long-term operation can lead to swollen SR and interfacial cavity defects, whose effects can be severe and unpredictable. This study aims to investigate the changes in dielectric and mechanical properties of SR caused by silicone grease absorption. We measure the dielectric properties by frequency domain dielectric spectroscopy (FDS) and dynamic mechanical analysis (DMA) is applied to evaluate the complex modulus and stress relaxation. The effects of molecular polarity and absorption content of silicone grease are specifically considered and evaluated. As a consequence, silicone grease absorption reduces storage modulus and loss modulus, and accelerates stress relaxation of SR insulation, probably leading to insufficient interfacial pressure which is considered a major concern for cable accessories. In addition, changes in dielectric properties are dependent on the absorption content and molecular polarity of silicone grease. The deterioration effect of fluorinated silicone grease is stronger than that of phenyl methyl silicone grease. These results can be attributed to the occupation of free volume and weakening of intermolecular forces in SR, which provides an understanding of deterioration mechanism of SR caused by silicone grease absorption.