Effect of ethylene–vinyl acetate copolymer on kinematic viscosity and thermal stability of jojoba, date seed, and waste cooking oils in lubricant applications

Vegetable oils possess excellent lubricant properties, but one reason limiting their application as lubricants is their low kinematic viscosity. This study investigated how the addition of ethylene–vinyl acetate copolymer could affect the kinematic viscosity and thermal stability of jojoba, date seed, and waste cooking oils. The yield of oil from jojoba and date seed was 51.7 ± 0.77% and 8.2 ± 0.5%, respectively. The oleic acid content in jojoba, date seed, and waste cooking oils was 3.09, 49.15, and 72.4%, respectively. Kinematic viscosity of date seed oil with 4% ethylene vinyl acetate was 178 ± 2.8 mm2/s at 40 °C, whereas the kinematic viscosities of jojoba and waste cooking oil with 4% ethylene vinyl acetate were 170 ± 2.1 and 165 ± 1.4 mm2/s at 40 °C. The addition of 4% ethylene vinyl acetate increased kinematic viscosities of date seed, jojoba, and waste cooking oils by a multiplication factor of 5.5, 6.8, and 4.7, respectively. Thermal stability was evaluated using decomposition temperatures. Onset decomposition temperature for jojoba, date seed, and waste cooking oils with ethylene–vinyl acetate was 344, 267, and 339 °C, and offset decomposition temperatures were 479, 474, and 450.6 °C, respectively. Offset decomposition temperature for jojoba and date seed oils without ethylene–vinyl acetate was 407 and 445 °C, whereas the onset temperature of industrial gear oil was 238 °C, and the offset temperature was 363 °C. Nevertheless, kinematic viscosity and thermal stability of vegetable oil–ethylene vinyl acetate blends were higher than those of industrial gear oil.