Continued from page 16
reaction of HR-PIB with maleic anhydride to make additive precursors. This is a high temperature chemical reaction at around 200°C and should not be misinterpreted as sensitivity to oxidation or generally to stability, especially not under conditions relevant for most industrial lubricants.
biodegradable, which allows formulation of lubricants complying with common eco-labels, e.g. EU ecolabel.
Coefficient of friction can be regarded as the indicator for energy efficiency. Water soluble PAGs show the lowest coefficients of friction in hydrodynamic lubrication of all common high-viscosity base oil types (figure 3).
Table 2: Blends of PIB with low-viscosity PAO
When PIB grades are blended with a low viscosity polyalphaolefine (PAO) (Table 2) the blend using HR-PIB (Blend A) has noticeably better shear stability as HR-PIB has a narrower molecular mass distribution avoiding shear unstable high molecular mass fractions. In various oxidative stability tests the formulation using HR-PIB always performed similar or even better than the formulation using conventional PIB.
Polyalkyleneglycols Polyalkyleneglycols (PAG) are synthesised by polymerisation of ethylene oxide (EO) and/or propylene oxide (PO). Mixtures of EO and PO result in the formation of EO-PO random co-polymers. With an EO content exceeding a certain level, these base oils are soluble in water. The PO content modifies the polymer properties, e.g. guarantees excellent low temperature properties. When PO is used as the sole monomer, the resulting base oils are insoluble in water and show only limited solubility in unpolar hydrocarbon base oil.
PAG base oils exhibit a wide range of excellent properties: extremely low coefficient of friction – especially water soluble PAGs, very high viscosity index, good oxidation stability, clean operation and sludge solubility due to their high polarity. They are highly shear stable and show excellent low temperature properties. They are low tox and often
18 LUBE MAGAZINE NO.153 OCTOBER 2019
Figure 3: MTM traction curve of various ISO VG 320 base oils
Water soluble and water insoluble PAGs are not compatible with Gr I-IV base oils and the incompatibility is sometimes regarded as a main hurdle for a more widespread use of PAGs.
The obvious way to chemically modify PAGs to allow miscibility is making them more lipophilic by reducing the amount of EO and incorporating longer chain alkylene oxides - like butylene oxide. A Polybutyleneoxide is indeed compatible with hydrocarbon base oils, but unfortunately such a polymer loses most frictional benefits. Therefore, achieving compatibility while maintaining frictional benefits requires a more significant chemical modification resulting in a completely new base oils structure.
This is accomplished with a new base oil technology called “energy efficient base stock” (EEB). EEB is compatible with low viscosity mineral oils, PAOs, esters and naphthenic oils and shows significant friction reduction versus high viscosity PAOs.
Figure 4: EEB is fully miscible with unpolar low viscosity base oils like PAO Continued on page 20
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