Q: What’s the main difference between PAOs & PAGs?
Let’s start off with definitions!
PAG: Polyalklene Glycol
While both are synthetic oils they are classified under different Groups of Base oils. PAOs have their own Base oil Group IV while PAGs fall into the Group V (catch all).
PAOs are actually hydrogenated oligomers of an α-olefin and there are different methods of oligomerisation. Due to this process, PAOs have very good low temperature properties and the products are wax free! Additionally, their lower volatilities also allow them to operate over a wide temperature range. Usually, they can be used in a lot of versatile applications such as gearboxes, screw compressors, fans, motors and even automotive!
However, PAOs have a low polarity which gives rise to poor solvency of polar compounds and issues with seal performance.1
On the other hand, PAGs can differ depending on their structure. For instance, Ethylene is water soluble while Propylene is not, however, neither are oil soluble. Both experience significant chemical reactions producing sludge like deposits when mixed with mineral oil.
Usually, their properties include a wide viscosity range, low pour points, good lubricity, low toxicity and non-flammable in aqueous solutions. PAGs are typically always found in fire-resistant hydraulic fluids as well as industrial gear oils, compressor lubricants, heat transfer liquids and metalworking fluids.1
Both products need to be tested for compatibility with mineral oils before any mixing occurs. Additionally, most lubricant suppliers deem PAOs & PAGS as “filled for life” solutions which last for a longer time compared to mineral oils. Typically, the purchase of these products are more expensive than mineral oils, however if one looks at the cost of waste disposal and reduced downtime (due to decreased shutdowns for oil changes) the overall cost of the lubricant is by far less than that of mineral oil.
- Chemistry and Technology of Lubricants 3rd Edition, Chapter 2, R.M. Mortier, M.F. Fox, S.T. Orszulik