PG vs PEG

SeanGAR · 07-26-2011, 06:31 PM

Propylene glycol and polyethylene glycol are absolutely not the same thing.

Propylene glycol is 3 carbons long with 2 hydroxyl groups, weighing 76 g/mole.

Polyethylene glycol is a polymer of variable lengths and molecular weights.

Polyethylene glycol 200 weighs ~200 g/mole and is liquid at room temperature while polyethylene glycol 20,000 is ~20,000 g/mole and is a white solid at room temperature. They differ in how many ethylene glycol molecules are in the polymer. Miralax is polyethylene glycol 3350, weighing (you guessed it) 3350 g/mole.

PEGs are different from ethylene glycol, which is the poisonous component of antifreeze (PEGs are ethylene glycol polymers).

You want propylene glycol if you're mixing for humidity control, but I prefer and recommend beads.

Bovedas are OK ... they use saturated salt solutions to control humidity the way we use saturated sodium chloride to test hygrometers (at 20-25 C, NaCl --> 75% humidity, NaBr --> 58-59% humidity). I forget what salts Boveda uses.

07-26-2011, 06:31 PM	#7
SeanGAR Crotchety Geezer Join Date: Oct 2008 Location: Radford VA Posts: 911 Trading: (3)	Re: PG vs PEG Propylene glycol and polyethylene glycol are absolutely not the same thing. Propylene glycol is 3 carbons long with 2 hydroxyl groups, weighing 76 g/mole. Polyethylene glycol is a polymer of variable lengths and molecular weights. Polyethylene glycol 200 weighs ~200 g/mole and is liquid at room temperature while polyethylene glycol 20,000 is ~20,000 g/mole and is a white solid at room temperature. They differ in how many ethylene glycol molecules are in the polymer. Miralax is polyethylene glycol 3350, weighing (you guessed it) 3350 g/mole. PEGs are different from ethylene glycol, which is the poisonous component of antifreeze (PEGs are ethylene glycol polymers). You want propylene glycol if you're mixing for humidity control, but I prefer and recommend beads. Bovedas are OK ... they use saturated salt solutions to control humidity the way we use saturated sodium chloride to test hygrometers (at 20-25 C, NaCl --> 75% humidity, NaBr --> 58-59% humidity). I forget what salts Boveda uses. __________________ How can you have any pudding if you don't eat your meat? Last edited by SeanGAR; 07-26-2011 at 06:38 PM.