Refrigerant Oils - types of additives?

[PeterPolyol]

Hey there. First, I'm not sure where we can discuss refrigerant oils, here seems like the place but if not please forgive me and move the thread to the appropriate arena.

Many years ago the refrigerant standards changed where mineral oils were being phased out for more universal options like POEs. While PAG has been used for years with HFC refrigerants like r134a, we're seeing high-pressure r410 systems call mainly for POE. POE seems to be most preferred as it is compatible with all refrigerants from the old CFCs, to HCFCs and HFCs.

I'm curious about these oils and their additive systems. There are obviously RO (rust-oxidation) additives and AW additives but what exactly are they? Also, some of the POE oils for refrigeration appear to have very low Viscosity Indices and peculiar viscometrics
eg.
A particular Refrigerant POE-150
KV40/100 - 148/14.1
VI - 91
Pour - -27C

These specs notably different than other POEs like Motor Oils based on POE. Are the refrigerant oils straight ester bases with no viscosity altering additives?

 

[Tom NJ]

The POEs used in refrigeration oils usually require branched acids for HFC miscibility when the viscosity is higher than about ISO 22. These branched acids, usually 3,5,5, trimethylhexanoic and/or 2-Ethylhexanoic acids, significantly lower the VI. An ISO 150 grade may contain 70+% of branched acids. VI Improvers are not used.

Many POE refrigeration oils contain no additives. When additives are used, the most common are yellow metal inhibitors and anti-oxidants, usually at very low levels. Anti-wear, anti-foam, and hydrolytic stability additives are also used in some formulations.

BTW, I've driven through Listowel on my way to Tarbert for the ferry across the Shannon to Killimer.

Tom NJ