CAAB wrote: ↑
Tue Jul 23, 2019 7:34 pm
Shelf life of PG is typically 2 years as far as I have seen. Do you use your PG up within that period or do you freeze the extra or something?
Have you read of the effects heat has on PG? Does it create new undesirable compounds?
Well, if properly stored it is stable well beyond 2 years. At cool temperatures, propylene glycol is stable in a well-closed container, but at higher than normal storage temperatures, in the open, it may oxidize, giving rise to products such as aldehydes, propionaldehyde, lactic acid, pyruvic acid. Propylene glycol is chemically stable when mixed with high proof ethanol (+75%), glycerin, or water; aqueous solutions may be sterilized by autoclaving without harm to the molecule. See Dow Chemical PROPYLENE GLYCOLS: http://bit.ly/310ecgt
In this post we are discussing, as per the title of the post 'Extraction Methods' so we need not bother countering contrived examples that have appeared in the popular press about heating PG in contrived experiments above 300F. We can examine that in another topic post. But the short of the long of it is: that stuff is just NIH grant funding junk science.
I store reagent PG at room temps for long periods. No issues. However, all my extractions, once finished and filtered are stored in my little Sears Apartment Fridge at 40F.