Lubricant Additives

Ashless Phosphorus-Containing Lubricating Oil Additives 109

estimate that the toxicity of the TCP now available commercially is ∼400 times less than that of
material available in the 1940s and 1950s, and a recent evaluation of the organophosphorus-induced
delayed neurotoxicity (OPIDN) of a commercial aviation gas turbine oil containing TCP was nega-
tive [170]. However, in view of past concerns, the use of TCP is now largely restricted to aviation gas
turbine oils. Most general industrial applications that require an aryl phosphate AW additive now use
the isopropylphenyl or, to a lesser extent, the tertiarybutylphenyl variants. In standard tests, neither
of these types display OPIDN from acute oral ingestion. There are, however, some differences in
the toxicity and the ecotoxicity behavior between the different aryl phosphates. For example, the
reproductive toxicity of the synthetic aryl phosphates, together with TXP, was recently studied in rats
(according to Organisation for Economic Co-operation and Development [OECD] method 422). Both
the isopropylphenyl phosphate and the TXP showed adverse effects at moderate to high dose levels,
but these were reversible when exposure ceased. The TBPP (produced according to reaction 3.2) did
not display any adverse effects.
Differences are also seen in ecotoxicity behavior. Owing to the high TPP content in the lower-
viscosity grades of the synthetic phosphates (particularly ISO VG 22 and 32), these products have
the worst ecotoxicity behavior. The tertiarybutylphenyl phosphates normally have a higher TPP
content than the corresponding grade of IPPP and therefore, of the synthetic phosphates, possess
relatively worse ecotoxicity. By comparison, the IPPPs generally show satisfactory behavior in these
tests. One ISO VG 46 isopropylphenyl phosphate-based AW/EP additive has, for example, been
approved by the German Environment Agency (Umweltbundesamt) for use in rapidly biodegradable
hydraulic fl uids, products that are eligible for the “Blue Angel” environmental award [171].
Another difference between the product types is displayed in biodegradability tests. The tests
were carried out according to OECD method 301F (Manometric Respirometry). In this test, bio-
degradation is measured as the net oxygen uptake over that occurring in blank tests containing only

TABLE 3.20

Guidance on the Selection of AW and EP Additives

Required Characteristic

Good AW

Performance

Good EP

Performance

Combination of AW

and EP Performance

Non-phenolic additive Neutral alkyl
phosphates; dialkyl
alkyl phosphonates

Acid alkyl phosphates;

acid alkyl

phosphonates and

their salts; neutral

and acid alkyl

phosphites

Mixtures of neutral and

acid phosphates, etc.

Good hydrolytic stability TXP, dialkyl alkyl
phosphonates

Acid alkyl

phosphonates and

their salts

—

Good oxidation stability Neutral tertbutylphenyl
phosphates

Hindered aryl

phosphites

—

Low foaming/air release Neutral phosphates,
dialkyl alkyl
phosphonates

Neutral phosphites —

Good toxicity performance Neutral tertbutylphenyl
phosphates

Acid IPPPs —

Good ecotoxicity
performance

Neutral IPPPs — —

Multifunctionality, for
example, rust inhibition,
antioxidant

Neutral and acid

phosphites, acid

phosphates

Acid IPPPs