Dielectric Performance and Structure–Property Relationships of Sodium Soap Grease Derived From Treated Waste Cooking Oil for Switchgear Applications

ABSTRACT This study investigates the development of a sustainable sodium soap‐based grease derived from treated waste cooking oil (TWCO) for application in low‐voltage electrical switchgear systems. In this context, this study introduces a sustainable dielectric grease system by linking grease microstructure to electrical insulation performance in switchgear applications. Emphasis is placed on understanding the structure–property relationships governing dielectric performance, where the interaction between TWCO triglycerides and the fibrous sodium soap network formed via in situ saponification plays a critical role. A series of grease formulations (SG40–SG75) with varying oil‐to‐thickener ratios were synthesized and evaluated through physicochemical and electrical characterization. Mechanical properties were assessed using consistency (ISO 2137), oil separation (ASTM D6184), oil bleeding, dropping point (ASTM D2265), and corrosion resistance (ASTM D4048). Electrical performance was determined using dielectric strength (ASTM D149), volume and surface resistivity (ASTM D257), and impedance spectroscopy. Among the formulations, SG60 (60 wt.% TWCO, 40 wt.% sodium stearate) exhibited the most balanced performance, achieving NLGI Grade 2 consistency, low oil separation (<1%), controlled oil bleeding, and a high dropping point (>225°C). Electrically, SG60 demonstrated high dielectric strength (22.5 kV/mm), elevated volume resistivity (>10 14 Ω cm), and stable capacitive behavior across the tested frequency range. The enhanced performance is attributed to the optimized macromolecular network, which restricts charge transport while maintaining structural integrity. These findings establish a structure–property framework for designing sustainable dielectric greases and highlight the potential of TWCO as a functional base fluid for electrical insulation applications.