Dispersants 163
diffuse into the seals. This will either cause a change in the seal’s hardness, thereby leading to
swelling and or elongation, or extract the plasticizer, an agent used to impart fl exibility and strength
to polymeric materials.
Abrasive damage is not common since most equipment has an installed lubricant fi ltration sys-
tem. The lubricant-related damage, however, is of primary interest to us. The lubricant is a blend of
base stocks and an additive package. Certain base stocks, such as those of high aromatics content
or those that are of the ester type, have the tendency to extract the plasticizer because of their high
polarity. Additives, however, have the ability to diffuse into the seal material and alter its properties
as well as remove the plasticizer. Among additives, dispersants are the most implicated in causing
seal damage, especially to fl uoroelastomer (Viton®) seals. Although in many cases seal failure can
be corrected by the use of additives, called the seal-swell agents, it is wise to eliminate such damage
by prevention. Elastomer compatibility requirements are a part of the current United States, Asso-
ciation des Contsructeurs Européens de l’Automobile (ACEA), and Japanese standards for engine
oils and worldwide automotive transmission and tractor hydraulic fl uid specifi cations [119]. Damage
to seals is prevalent in the case of nitrogen dispersants. In general, the higher the nitrogen content,
the higher the seal problems [118]. Rationally, these problems occur due to the presence of low-
molecular-weight molecules in the dispersant. These include free amine either as such or in a labile
form, such as an alkylammonium salt, or low-molecular-weight succinimides and succinamides.
Because of their high polarity and smaller size, these molecules are more likely to diffuse into the
seal material and alter its physical and mechanical properties [120]. It is believed that in the case of
Viton seals, the loss of fl uoride ions is responsible for seal deterioration. Removal of the free amine
and of low-molecular-weight succinimides will improve seal performance. Alternatively, one can
posttreat dispersants with reagents, such as boric acid and epoxides, which will either make
such species innocuous or hinder their diffusion into the seal material. Many chemical treat-
ments of dispersants, covered in Section 5.7.1, claim to improve seal performance of dispersants
and crankcase lubricants that use them. These reagents react with seal-damaging amines and low-
molecular-weight succinimides to make them harmless. Strategies other than those listed earlier are
also reported in the patent literature [121–125].
5.8 PERFORMANCE TESTING
Engine oils account for almost 80% of the automatic transmission dispersant use. Other applica-
tions that use these additives include automatic transmission fl uids, gear lubricants, hydraulic fl uids,
and refi nery processes as antifoulants. Dispersants of relatively lower molecular weight are also
used in fuels to control injector and combustion chamber deposits [126,127]. Such dispersants usu-
ally contain a polyether functionality [128].
Succinimide and succinate ester–type polymeric dispersants are used in gasoline and die-
sel engine oils, but the use of alkylphenol-derived dispersants, that is, of the Mannich type, is
limited to gasoline engine oils. Dispersant polymers derived from ethylene–propylene rubbers,
styrene–diene copolymers, and PMAs are also used in both gasoline and diesel engine oils. As
mentioned earlier, dispersant polymers lack suffi cient dispersancy to be used alone and hence are
used in combination with polymeric dispersants. The PMA and styrene ester–derived dispersant
polymers are used in automatic transmission fl uids, in power-steering fl uids, and, to a limited
extent, in gear oils.
Additive manufacturers use various laboratory screen tests and engine tests to evaluate a
dispersant’s effectiveness. Many of the screen tests are proprietary, but all are developed around
evaluating performance in terms of a dispersant’s ability to disperse lamp black or used engine oil
sludge. The laboratory engine tests are industry-required tests and include both gasoline engine
and diesel engine tests. These are listed in International Lubricant Standardization and Approval
Committee (ILSAC), American Petroleum Institute (API), ACEA 2002, Japanese Automobile
Standards Organization (JASO), and Bureau of Indian Standards (BIS) standards. It is important