I've always thought that since the propellant is a solvent of sorts, composed of hydrocarbon, the plastic, which is also a hydrocarbon, absorbs the solvent, and become soft.
This is very true, the two hydrocarbons mix and one partially solubilizes the other.
It has been said before that it is the petroleum distillates (aka hydrocarbons) that are the problem with non-food grade silicone sprays, this is true and makes makes sense for a variety of reasons. 1. petroleum distillates solubilize plastic, this is why people describe their cube as being sticky right after they spray in the lube and 2. petroleum distilates will evaporate quickly, their evaporation is why the cube stops being sticky after a while.
If you look at the product description for
CRC's Heavy Duty Silicone lubricant you will see that it contains hydrocarbons (petroleum distilates) and is
not plastic safe
The product description for
Food Grade Silicone (Aerosol) says it is '
Safe on Most Plastics' and does not say it includes hydrocarbons/petroleum distilates though it does contain HFC-152a which is 1,1-Difluoroethane, a hydrocarbon derivative that I am not familiar with but must be plastic safe.
If you want to be incredibly sure that you don't hurt your Rubik's cube plastic I would go with
Food Grade Silicone (Non-Aerosol) since it does not have any sort of petroleum distilates/hydrocarbons or hydrocarbon derivatives (because it is non-aerosol), some sort of
Silicone Shock Oil or the Rubik's/PuzzlePro silicone lube (which is apparently
JohnsonDiversy Shine Up Furniture Polish, though I can't confirm this)
If you can't find food grade silicone or silicone shock oil and only have the silicone spray with petroleum distilates in it (this includes Jig-a-Loo) then you should
definitely disassemble your cube and spray on the silicone spray so that the petroleum distilates evaporate quickly. I would even consider using a hair dryer to make them evaporate quicker (provided it doesn't heat up the plastic too much).
Another thing that I have thought of, but never tried is to spray your non-food grade silicone spray into some sort of glass or porcelin bowl and allow the hydrocarbons to evaporate and
then apply the remaining (probably pure silicone) onto your cube. This would probably be messy though.