Antioxidative Activity of 5-n-Pentadecyl-2-tert-butylphenol Stabilizers in Mineral Lubricant Oil

This work shows the synthesis, characterization, and thermo-oxidative study of 5-n-pentadecyl-2-tert-butylphenol [alkylphenol (AP)] before and after its incorporation into mineral lubricant oil. AP was synthesized by alkylation of hydrogenated cardanol. For this study, we employed thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), and differential thermal analysis (DTA) techniques. Mineral lubricant oil was submitted to an accelerated oxidation test in the presence and absence of AP according to the modified ASTM D-2440 method. The addition of 1% AP to the oil has reduced the carbonyl and peroxide band areas: 1.00−1.00 (without AP) and 0.35−0.32, ROOH; 0.53−0.59, CO (with AP), respectively. The results showed that AP significantly reduced the formation of oxidation products in the lubricant oil analyzed. TG−DTG curves showed that 5-n-pentadecyl-2-tert-butylphenol is more stable than 2,6-di-t-butyl-4-methylphenol (BHT), 158 against 87 °C for BHT. According to the integral procedural decomposition temperature (IPDT) values calculated on the basis of the TG thermograms, AP (IPDT of 268 °C) was recognized to be more thermally stable than BHT (IPDT of 162 °C). The techniques used for thermo-oxidative studies (TG−DTG, DSC, and DTA) showed a good correlation.