Lubricant Additives

110 Lubricant Additives: Chemistry and Applications

inoculated medium. The extent of biodegradation is calculated from the mass of test material added
to the test vessels and its theoretical oxygen demand for complete biodegradation. The test was car-
ried out in triplicate on the ISO VG 46 grades of different types of aryl phosphates manufactured
according to reaction 3.2. The results are summarized in Table 3.21.
The results are initially in the order of their hydrolytic stability, but it is interesting that TXP,
after a slow start, eventually reaches the same level as the synthetic fl uids and might have exceeded
them had the test been extended.
In view of these data, the tertiarybutylatedphenyl phosphate would be regarded as readily biode-
gradable (Pw1), whereas the TXP and IPPP would be classifi ed as inherently biodegradable (Pw2).
Despite of relatively benign ecotoxicity of the higher viscosity grades of aryl phosphates, all
these products are classifi ed as marine pollutants because of the UN Marine Pollutant Classifi cation.
However, because they are used at low concentrations, they are unlikely to contribute signifi cantly to
the fi nished product’s ecotoxicity.
The toxicity of other phosphorus-containing compounds is less well documented. Drake and
Calamari [172] indicate that dialkyl alkyl phosphonates generally have a low level of acute toxicity,
which decreases with increasing chain length, apparently a general observation for these classes of
compounds. As with alkyl phosphates, certain short-chain products can be skin irritants. No clues
were found to their environmental behavior, but in view of the absence of phenolics and improved
hydrolytic stability, it might be surmised that fi sh toxicity could be good but biodegradability would
be inferior to that of the phosphates. Neutral phosphites, particularly the alkyl phosphites, would be
expected to have good toxicity and biodegradability behavior, but their ease of hydrolysis, which is
the factor assisting the biodegradation, would probably result in poor aquatic toxicity. The future of
the nonylphenyl phosphites is uncertain; the U.S. National Toxicology Program currently lists non-
ylphenol as an estrogen mimic and also as a thyroid disruptor. The acid phosphates, acid phosphites,
and their salts, particularly amine salts, are likely to be classifi ed as irritants and, due to their ease
of hydrolysis, may again be toxic to aquatic organisms. In all cases, it is essential that reference be
made to the health and safety information provided by the manufacturer.

3.8 THE FUTURE FOR ASHLESS PHOSPHORUS-BASED

LUBRICATING OIL ADDITIVES

Although ashless phosphorus-containing additives are used in many industrial applications, there
are certain market segments where they have not, to date, been successful. These are principally
in automotive engine oils where the use of ZDDP dominates due to a combination of price and
multifunctionality and in gear oils where sulfur continues to be the EP additive of choice. However,
the use of chlorine as an EP additive, particularly in metalworking applications, is in decline for
environmental reasons and is expected to be slowly substituted by P/S combinations. The use of sul-
fur alone in applications requiring high EP performance may also move to P/S mixtures to reduce
the total sulfur level and the ability to more readily “tailor” the balance of AW and EP performance

TABLE 3.21

OECD 301F Biodegradability Data on Different

Types of Aryl Phosphates

Product (ISO VG 46

Base Stocks)

% Biodegradability After

10 Days 28 Days 68 Days

TXP 5 29 70

IPPP 18 47 65

TBPP 25 62 72