Lubricant Additives

108 Lubricant Additives: Chemistry and Applications

be given prime consideration when taking these secondary requirements into account. Products that
demonstrate better AW than EP activity, and vice versa, are shown. However, the boundary between
AW and EP performance is not clear-cut and much depends on the application requirements.

3.7 TOXICITY AND ECOTOXICITY

It was mentioned earlier in this chapter that concern had been expressed in the past regarding
the toxicity of phosphorus-containing products, particularly TCP. Today, with increasing focus on the
environmental behavior of chemicals, their ecotoxicity is also under scrutiny. As a result, detailed
investigations into both the toxicity and the ecotoxicity have been carried out on alkyl and aryl phos-
phate esters. The results are summarized in recent publications [59,167], and most are available in the
safety data sheets associated with different product types. The data demonstrate a relatively low (but
variable) order of toxicity and ecotoxicity. No signifi cant risks in handling are anticipated, provided
the manufacturer’s guidance, which is essentially the same as for mineral oils, is followed.
The concerns over TCP arose as a result of the o-cresol content in the feedstock as tri-ortho-
cresyl phosphate (TOCP) was found to be a signifi cant neurotoxin. Initially, the level of o-cresol in
the feedstock was high (up to ∼25%) and signifi cant amounts of TOCP were present in the fi nished
product. Although the initial focus was on TOCP, it was later acknowledged that any isomer con-
taining the o-cresyl moiety was neurotoxic (e.g., mono-o-cresyldiphenyl phosphate was said to be
10 times more neurotoxic than TOCP [168]). For these reasons, the o-cresol content of the feedstock
used in the manufacture of TCP has been progressively reduced over time. In recent years, production
has moved to the use of 99% minimum m- and p-cresol. Levels of o-cresol in the feedstock are now
frequently <0.05%, and the TOCP content can be as low as parts per billion. Mackerer et al. [169]

TABLE 3.19

Principal Applications for Ashless Phosphorus-Containing AW/EP Additives

Application

Triaryl

Phosphate

Trialkyl

Phosphate

Amine

Phosphate

Acid

Phosphates

Alkyl/Aryl

Phosphites

Automotive

AT F 



Gear oil 


Power steering 


Shock absorber 


Electric motor 


Industrial

Hydraulic oils 



Gear oil 




Turbine oils 



Compressor oils 


Gas oil 



Universal tractor 


Metalworking 






Grease 




Way oils 


Circulating oil 


Vegetable oil 


Aircraft

Piston engine 


Turbine engine 


Grease