JHZR2
Staff member
Originally Posted By: Ben99GT
Originally Posted By: JHZR2
Just having esters or something does not mean much.
It kind of does though, esters are going to compete with oxidation and varnish for surface area, something PAO and Group III won't do by themselves. The fact that RL has a comparatively high ester content combined with a pretty stout detergent/dispersant package should make it a good cleaner by motor oil standards.
That depends. Just because something is an ester does not mean that it is competing for surface. They could have preferential coordination in groups, on other things (particulates, certain chemistries, etc.) or other applications.
Going back to MolaKule's Ester primer:
Quote:
Generally speaking, the higher molecular weight products of an oil show higher viscosities, but that only half of the story since the molecular "structure" also affects the molecular weight. Take the VII molecules of polymthylacrylates. These are high molecular weight structures that cause the formulated oil to become more viscous as temperature rises because of uncoiling at higher temperatures.
Ester may contain high or low molecular weight components as well, and may have KV's of 2 cST to over 100 cSt at 100 C. In esters, the structures are more important than molecular weight (except of course in determining final base viscosity).
When developing esters, particular attention is paid to ester structure. Short linear chains show better oxidative stability, whereas increasing the acid chain length of the molecule improves (decreases) the coefficient of friction.
This why Di- and Pentaerithyritol esters (PE's) are better (more stable) than Trimethylpropane (TMP) esters, and why TMP is better than Neopentylglycol (NPG) esters. The PE's have short chains of linear acid chains with make the ester more oxidatively stable and exhibit lower coefficients of friction.
If the ester is made from linear branched acids, the ester has higher flash points; increasing the molecular weight (making the ester molecule more compact) will also increase the flash point.
Representative esters:
Phthalates - Used mainly in air compressors; short fat molecule results in VI v.s pour point tradeoff.
Trimellitates - Short, branched esters that have high flash points and low volatilities and good thermal stability. Used when you need to leave a soft film behind.
Dimerates - Made from the acid of tallow oils and an alcohol (is three-branched); Has excellent lubricity and thermal and oxidative stability; used mainly in 2-stroke oils.
Polyols - SPE's, PE's, TMP's, TME's, and NPG's. Three or more shortchain but fat molecules. Polyols are generally more oxidative and thermally stable by 50 C over diesters and 150 C over petroleum oils. These esters have lower coefficients of friction than either diesters or PAO's.
By adding a polyol ester at least 5-10% to a PAO or mineral oil reduces base oil friction remarkably. So esters are natural Friction Modifiers.
Advanced esters can also BE USED AS VII improvers. Unlike long-chain polymers (such as methacrylates), complex polyols do NOT EXHIBIT the temporary loss of viscosity under forces exterted by shear, as in gears. Because complex esters are shorter chain molecules, they tend not to shear into smaller molecules.
Adding amine "backbones" to ester molecules allows them to have better antioxidant capabilities.
So you can see that the functionality of esters may or may not have the basis of competing for surface. The combination of stearic hinderance, large molecules (which fold to minimize energy and may not be able to approach a surface in a straightforward way), etc. effect the scenarios. Just because esters are present does not mean that their functionality will automatically adsorb them to a surface, or that the blenders intended for them to do this. There is a chance that this might happen, but it is a function of access and surface energies, which may or may not be favorable, and which may change depending upon how the chemistry of the oil and surface changes.
Originally Posted By: JHZR2
Just having esters or something does not mean much.
It kind of does though, esters are going to compete with oxidation and varnish for surface area, something PAO and Group III won't do by themselves. The fact that RL has a comparatively high ester content combined with a pretty stout detergent/dispersant package should make it a good cleaner by motor oil standards.
That depends. Just because something is an ester does not mean that it is competing for surface. They could have preferential coordination in groups, on other things (particulates, certain chemistries, etc.) or other applications.
Going back to MolaKule's Ester primer:
Quote:
Generally speaking, the higher molecular weight products of an oil show higher viscosities, but that only half of the story since the molecular "structure" also affects the molecular weight. Take the VII molecules of polymthylacrylates. These are high molecular weight structures that cause the formulated oil to become more viscous as temperature rises because of uncoiling at higher temperatures.
Ester may contain high or low molecular weight components as well, and may have KV's of 2 cST to over 100 cSt at 100 C. In esters, the structures are more important than molecular weight (except of course in determining final base viscosity).
When developing esters, particular attention is paid to ester structure. Short linear chains show better oxidative stability, whereas increasing the acid chain length of the molecule improves (decreases) the coefficient of friction.
This why Di- and Pentaerithyritol esters (PE's) are better (more stable) than Trimethylpropane (TMP) esters, and why TMP is better than Neopentylglycol (NPG) esters. The PE's have short chains of linear acid chains with make the ester more oxidatively stable and exhibit lower coefficients of friction.
If the ester is made from linear branched acids, the ester has higher flash points; increasing the molecular weight (making the ester molecule more compact) will also increase the flash point.
Representative esters:
Phthalates - Used mainly in air compressors; short fat molecule results in VI v.s pour point tradeoff.
Trimellitates - Short, branched esters that have high flash points and low volatilities and good thermal stability. Used when you need to leave a soft film behind.
Dimerates - Made from the acid of tallow oils and an alcohol (is three-branched); Has excellent lubricity and thermal and oxidative stability; used mainly in 2-stroke oils.
Polyols - SPE's, PE's, TMP's, TME's, and NPG's. Three or more shortchain but fat molecules. Polyols are generally more oxidative and thermally stable by 50 C over diesters and 150 C over petroleum oils. These esters have lower coefficients of friction than either diesters or PAO's.
By adding a polyol ester at least 5-10% to a PAO or mineral oil reduces base oil friction remarkably. So esters are natural Friction Modifiers.
Advanced esters can also BE USED AS VII improvers. Unlike long-chain polymers (such as methacrylates), complex polyols do NOT EXHIBIT the temporary loss of viscosity under forces exterted by shear, as in gears. Because complex esters are shorter chain molecules, they tend not to shear into smaller molecules.
Adding amine "backbones" to ester molecules allows them to have better antioxidant capabilities.
So you can see that the functionality of esters may or may not have the basis of competing for surface. The combination of stearic hinderance, large molecules (which fold to minimize energy and may not be able to approach a surface in a straightforward way), etc. effect the scenarios. Just because esters are present does not mean that their functionality will automatically adsorb them to a surface, or that the blenders intended for them to do this. There is a chance that this might happen, but it is a function of access and surface energies, which may or may not be favorable, and which may change depending upon how the chemistry of the oil and surface changes.
