Why Use PAOIL?
The Chemical and physical interaction between PAG and our PAO based oils is effectively zero, because of the difference in chemical structure of the oils.
Our PAO oils are stable, chemically inert, non-polar and hydrophobic while PAG's are polar, absorb water and are susceptible to hydrolysis. PAOs will not alter the stability of a PAG. As a consequence of the polarity difference PAGs and PAOs are not miscible and any PAG/PAO mixture in refrigeration system will consist of discrete droplets of the minor oil in a matrix of the major component. This immiscibility will limit the opportunity for chemical interaction.
The stability/inert nature and hydrophobicity of ROC oil is a consequence of the chemical structure of the base PAO oil.
Polyalpha olefins are made by first polymerizing olefin hydrocarbons and then hydrogenating the product oil to remove any residual reactivity. Breakdown of a PAO involves breaking carbon-carbon or carbon-hydrogen bonds which requires high temperatures; they are branched paraffins.
In contrast PAGs have short hydrocarbon sequences joined by ester or ether bonds; in use these bonds are susceptible to the action of acid or water which break the molecular chain and form acidic groups.
The acid groups in turn attack further bonds resulting in loss of viscosity and catastrophic failure of the lubricant.
We now have many measurements of the moisture content of ROC oils performed by Oilcheck Pty Ltd by the Coulometric Karl Fischer method ASTM D6304. Although we take no precautions to prevent moisture absorption in our production process, our results for unused product oil fall within the range 20 - 50 ppm water. Even an oil stored for many years had only 53ppm moisture.
In contrast the unused, freshly-opened POE cited in the paper had 308ppm.
There is ample evidence of the low hygroscopicity of PAOs. PAO water contents are one-tenth that of POEs or PAGs. (lan has a graph of the rate of moisture absorption)
"Compatibility" in the context used in the paper means that in practice ROC can be used in a system containing residual PAG or POE without detriment to performance of the system. ROC is fully miscible with POE but not miscible with PAG. Despite this, customers replacing PAG with ROC in Auto aircon system are happy with the performance of the system and complaints are rare.