Free radical scavenging antioxidant
Phenolic antioxidants were first used in lubricating oils. The combination of phenolic antioxidants and ZDDP has a good synergistic effect, because phenolic compounds are free radical scavenger and ZDDP is peroxide decomposer. Phenolic compounds can prolong the oxidation induction period of ZDDP and thus improve the antioxidant performance of lubricating oil. There are many phenolic antioxidants, and the phenolic antioxidants with good thermal stability include different alkyl blocked phenols, blocked phenolic esters containing thioether, polycyclic blocked phenols and alkyl thiophenols. Such as shielding phenol ash-free antioxidants [3 - (3, 5-2 tertiary butyl - 4 - hydroxy phenyl) acrylic diisooctyl] is a good oil solubility and high temperature oxidation resistance excellent ash-free antioxidant, it not only has good oxidation resistance, and has good control ability of sludge formation, with the rest of the lubricating oil additive has good compatibility and compatibility. Containing sulfide type structure of hindered phenolic antioxidants in API Ⅱ, Ⅲ class base oil of antioxidant effect is good. For example, the antioxidant containing sulfoether monophenol can effectively solve the high temperature antioxidant performance of high-grade oil, so that the high-grade oil through the relevant engine bench test, this kind of product has a higher thermal decomposition temperature. Glucosinolates bisphenol type antioxidants (such as 2246 - SbasfIrganoxL115) is a kind of multi-purpose, non-polluting antioxidant, shield phenol sulfur atom and synergistic effect, makes it have excellent oxidation resistance and solubility, and its antioxidant effect is better than that of ordinary single structure of phenolic antioxidants, in the hydrogenation base oil showed good antioxidant properties, and can significantly inhibit the nitro oxidation. Table 2 shows the antioxidant effects of different phenolic antioxidants in base oils (mass fraction of antioxidants is 0.25%) by rotating oxygen bomb method (SH/T0193).