Aliphatic Esters - Properties and Lubricant Applications

Abstract

N 1942 this laboratory undertook a basic investigation of the I problems involved in low temperature instrument lubrication.The results obtained using aliphatic diesters as lubricants have been reported (1-5, 6, 7,16, 25). It was found that a number of aliphatic branched-chain diesters possessed the requisite properties, for not only the lubrication of instruments but also many other military applications in aircraft and ordnance equipment. During the corresponding period, a German research group under the leadership of Zorn (58) investigated independently the use of esters as special-purpose lubricants and concluded that several branched-chain aliphatic esters were outstanding. Their work was later reviewed by Tingle (56) and by Horne (18).Since World War 11, a variety of special lubrication problems have arisen which increased interest in synthetic lubricants. Aircraft gas turbines, for example, require oils capable of providing adequate lubrication from temperatures of -65" to about 275" F. with temperatures on shutdown as high as 500" F. for intervals of 1 or 2 hours. Military automotive equipment is required t o operate a t what m-ere formerly considered prohibitively low temperatures (19). At high altitudes or in winter, machine guns and automatic cannon frequently could not be made to f i e because of congealed lubricants (56). Synthetic ester lubricants have received increasing application where petroleum lubricants cannot function satisfactorily. Therefore, this laboratory has endeavored, through its own research and through encouragement of industry, to extend the supplies of such lubricants by locating additional sources of native raw materials for their production and by developing new classes of esters (27). This report summarizes the progress since earlier publications (3, 6).Certain generalizations relating the structures of hydrocarbons to their viscometric properties were found valid for esters (6, 6, 8 25, 32, 32). These researches resulted in structural guides which reduced substantially the number of compounds required for synthesis and study. It was found that the high viscosity indexes of long-chain molecules are due to their ability to coil and uncoil reversibly with variations in temperatures ( I d , 31, 32).Such coiling is possible because of the freedom of rotation about the chemical bonds in the principal chain. Branching restricts the rotational freedom about these bonds and also increases the ratio of cross section to length of the molecule, both effects contributing to smaller viscosity indexes. Unbranched diesters have slightly lower viscosity indexes than the analogous hydrocarbons because the carbonyl oxygen behaves as a short branch chain.Unusual surface active properties-viz., ability to adsorb and orient at the solid-liquid interface, forming good wear-preventive f i l m e w e r e attributed to the diesters by Zorn (58). Brophy and Zisman (8) showed that the wear-preventive and rust-inhibiting properties of diesters were caused by the presence of impurities, as the pure compoun...

Inhibition of Polyglycol Autoxidation.

“…At temperatures of 150°C. and higher, most conventional antioxidants lose their efficacy (9), probably because of their inherent susceptibility to direct oxidation by oxygen (20). Of the group of antioxidants examined in this study, only phenothiazine and AgeRite Resin D show much efficacy at 150°C.…”

Factors Influencing the Lead Corrosivity of Ester Oils during Long-Term Storage.

“…A fortunate circumstance made it possible to supplement the storage tests just described with data on well-characterized diesters which had been stored under laboratory surveillance for as much as 14 years. These were retained samples of diesters procured and tested in connection with the original development of the diester instrument and engine oils (3,4,7). The current properties and corrosivities of these samples are shown in Table I.…”

Structural Effects of Arylstearic Acids as Combination Oxidation and Rust Inhibitors

“…The hydroxyarylstearic acids at 150°C. are not as effective on an equivalent concentration basis as phenyl-1-naphthylamine or phenothiazine (2,8). The advantage gained in the use of a single additive to replace a dual inhibitor system is rather obvious in simplifying the blending process and preventing possible side effects such as interaction of additives.…”