Novel Technique to Understand the Interaction of Silicone Oil and Grease With Silicone Rubber for Cable Accessories

This paper attempts to comprehensively understand Liquid Silicone Rubber (LSR) interaction with silicone oil and grease using physicochemical analyses and the Frequency Domain Spectroscopy (FDS) technique. Silicone oil and grease are extensively used in cable accessories i.e. joints and terminations. The weight gain analysis shows that LSR absorbs silicone oil faster than silicone grease and its absorption rate increases with temperature. The absorption process follows Langmuir diffusion model. Fourier Transform Infrared (FTIR) analysis shows no change in the chemical properties in the operating temperature range. The thermal stability of the samples decreases with a higher rate of absorption as evident from Thermogravimetric Analysis (TGA). Differential Scanning Calorimetry (DSC) study reveals that the Melting Temperature (T<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub>) increases with absorption. Surface hardness decreases with a higher absorption rate as measured using Shore-A Durometer. Microscopic level ingress has been confirmed from the Atomic Force Microscopy (AFM) analysis, where the surface roughness reduces with the higher ingress of oil/grease. Electrical performance of the samples is evaluated using Frequency Domain Spectroscopy (FDS). The Dielectric Dissipation Factor (DDF), tanδ, increases with absorption, denoting higher polarization losses. To further analyze the polarization mechanisms with absorption, the Havriliak–Negami (H–N) model has been used. The sensitivity of absorption in the parameters of H–N model has been used to develop a mathematical model to estimate the oil and grease content in LSR samples. FDS measurements are further analyzed to determine the Activation Energy (EA) of the samples, beneficial for understanding the long-term performance of LSR samples.