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Volatility: The polarity of the ester
molecules causes them to be attracted to one another and this intermolecular
attraction requires more energy (heat) for the esters to transfer from a
liquid to a gaseous state. Therefore, at a given molecular weight or
viscosity, the esters will exhibit a lower vapor pressure which translates
into a higher flash point and a lower rate of evaporation for the lubricant.
Generally speaking, the more ester linkages in a specific ester the higher
its flash point and the lower its volatility.
Lubricity: Polarity also causes the
ester molecules to be attracted to positively charged metal surfaces. As a
result, the molecules tend to line up on the metal surface creating a film
which requires additional energy (load) to penetrate. The result is a
stronger film which translates into higher lubricity and lower energy
consumption on lubricant applications.
Detergency/Dispersency: The polar
nature of esters also makes them good solvents and dispersants. This allows
the esters to solubilize or disperse oil degradation by-products which might
otherwise be deposited as varnish or sludge, and translates into cleaner
operation and improved additive solubility in the final lubricant.
Biodegradability: While stable against
oxidative and thermal breakdown, the ester linkage provides a vulnerable
site for microbes to begin their work of biodegrading the ester molecule.
This translates into very high biodegradability rates for ester lubricants
and allows more environmentally friendly products to be formulated.
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