6. Bio-based antioxidants and lubricants

lubricating systems that involve a synergistic mechanism, free radical scavengers are the major antioxidant component, while the hydroperoxide decomposers function as auxiliary components for the free radicals [38]. It was reported that the oil-soluble organic molybdenum (organic molybdenum complex (MC)) and arylamine antioxidant (dioctyldiphenylamine (DO-DPA)) would have an excellent antioxidant synergism in an oil system (poly-alphaolefin synthetic lubricant (PAO)) as shown in the DSC thermogram (Figure 16). The OIT was increased from 221.4C with DODPA as the sole antioxidant to 229.7C with the combination of DODPA and MC as the synergistic antioxidants. Also, a lower acid generation and lower kinematic viscosities were observed after oxidation-corrosion test for the lubricant with antioxidant, especially in the lubricant with both DODPA and MC due to their synergistic impact (Table 3). As a consequence, a lower deposit occurs when both antioxidants are in the system

In another study by Hu et al. [39] where a molybdate ester (ME) and dioctyldiphenylamine (DO-DPA) were used as antioxidants, a synergistic effect was reported between the two antioxidants.

Synergistic behavior of sulfonated calcium carbonate and an ashless antioxidant (N-phenyl-αnaphthylamine (T531)) in hydrogenated oil was investigated and the results suggested that

Figure 16. DSC thermograms of PAO oxidation in the presence of DODPA with or without MC [38]. Reprinted by

Lubricant ΔTAN ΔKV (%) Polyalphaolefin (PAO) 8.2 216 PAO + 0.5% MC 5.6 180 PAO + 1.0% DODPA 3.6 36.8 PAO + 1.0% DODPA +0.5% MC 2.1 15.3

permission of the Society of Tribologists and Lubrication Engineers, www.stle.org.

ΔTAN: change in the total acid number; ΔKV: change in the kinematic viscosity.

Table 3. The change in total acid number and viscosity after 24 h in oxidation-corrosion test [38].

anti-wear and antioxidant effect were synergistically improved in the system [40].

(Figure 17) compared with the lubricants that contain DODPA solely.

36 Lubrication - Tribology, Lubricants and Additives

Triglycerides from plant sources have been used as biolubricants with limited applications due to their low thermal and oxidative stability. As well, triglycerides have low volatility, high lubricity, low toxicity and good viscosity-temperature properties as their key advantages. Therefore, different antioxidants such as tocopherols, propyl gallate (PG), ascorbyl palmitate (AP), and some synthetic antioxidants (butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), mono-tert-butylhydroquinone (TBHQ), or 4,4<sup>0</sup> -methylenebis(2,6-di-tert-butylphenol) (MBP)) have been used to improve their resistance to the oxidative agents. In recent years, a great number efforts have been made to develop sustainable bio-lubricants and additives wit the preference of non-toxicity, multi-functionality and compatibility to the present systems. Cellulose fatty esters have been developed as the lubricant additive, mainly for antioxidant applications. It has been modified to cellulose ferulate, cellulose lipoate and αtocopherulate for antioxidant functionality [42, 43].

In a study by Singh et al. [44], cellulose laurate was synthesized for use as an effective biolubricant. The results indicated that the lubrication performance would increase with the degree of substitution (DS) in cellulose molecule and by increasing the concentration of cellulose laurate in the base oil which was n-butyl palmitate/stearate.

In another study [45], a multi-function additive as detergent/dispersant/antioxidant/anti-wear was developed from L-histidine (HDS) for bio-lubricant applications. Two types additives namely, Ca-HDS-L and Ca-HDS-M were synthesized by esterification with lauroyl chloride and myristoyl chloride, respectively. Using the products in a polyol base oil indicated that Ca-HDS-L worked as a better detergent and dispersant, but Ca-HDS-M functioned as a more effective antioxidant. The oxidative properties obtained by the two additives (ca. 1–3 g/l addition to the oil) are presented in Table 4.

Author details

Majid Soleimani1

References

Saskatoon, SK, Canada

16.09.2017]

6522-6526

\*, Leila Dehabadi<sup>2</sup>

\*Address all correspondence to: mas233@mail.usask.ca

, Lee D. Wilson<sup>2</sup> and Lope G. Tabil1

Antioxidants Classification and Applications in Lubricants

http://dx.doi.org/10.5772/intechopen.72621

39

1 Department of Chemical and Biological Engineering, University of Saskatchewan,

2 Department of Chemistry, University of Saskatchewan, Saskatoon, SK, Canada

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Table 4. The effect of multi-function additives (Ca-HDS-L and Ca-HDS-M) on quality properties of a polyol lubricant in universal oxidation test (IP 306); TAN: Total acid number [45].
