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Propylene Glycol Concentration for 65% RH

FoMoCo

FoMoCo

Member
Joined
Apr 4, 2008
Messages
118
I have searched for information on using PG to maintain a RH level of 65% with little success. I have found differing opinions on the feasibility of this but without any confirmation either way. So I thought I would run a brief test to investigate it for myself. I prepared PG / distilled water solutions with concentrations of 80/20, 67/33, and 50/50. I applied the solution to oasis foam and sealed them in a Tupperware container with a calibrated hygrometer. I am not a scientist, but I did try to control the variables in testing such that the only significant change was the PG / water concentration.

Results:
50/50 = 70% +/-1 - baseline
67/33 = 65% +/-1
80/20 = 60% +/-1

Questions:
Did I miss the thread that already covered this?
Anyone else using PG to maintain 65%?
Are these experimental results expected theoretically?

Before you reply with "Get 65% beads", I am aware of the bead products and may try them in the future. However, I had PG and distilled water on hand and was curious if it would maintain 65% RH.
 
FoMoCo said:
I have searched for information on using PG to maintain a RH level of 65% with little success. I have found differing opinions on the feasibility of this but without any confirmation either way. So I thought I would run a brief test to investigate it for myself. I prepared PG / distilled water solutions with concentrations of 80/20, 67/33, and 50/50. I applied the solution to oasis foam and sealed them in a Tupperware container with a calibrated hygrometer. I am not a scientist, but I did try to control the variables in testing such that the only significant change was the PG / water concentration.

Results:
50/50 = 70% +/-1 - baseline
67/33 = 65% +/-1
80/20 = 60% +/-1

Questions:
Did I miss the thread that already covered this?
Anyone else using PG to maintain 65%?
Are these experimental results expected theoretically?

Before you reply with "Get 65% beads", I am aware of the bead products and may try them in the future. However, I had PG and distilled water on hand and was curious if it would maintain 65% RH.
Click to expand...


No idea bro but I do know that 50/50 PG solution is supposed to regulate humidity around 70% but never was all that effective for me.. I started believing it was a gimmic, dropped it and bought myself some hassle free beads.

In my experience the PG added a slight taste to the cigars and gave them a little sheen... that's when I stopped using the PG solution some people like the taste and think shiny cigars are quality but I've yet to see a shiny one in full plume.
 
Nice experiment. Thank you!

I don't have this information at hand but your proportions are moving in the right direction. Since 100% water will regulate at 100% RH, it stands to reason that it would take a substantial reduction of the water proportion to nudge it down. What your results imply, is that a PG/water solution can vary quite significantly in proportion and still maintain humidity in an acceptable range. This is, in fact, the greatest advantage that PG/water has over any gel or silica-based humidity buffering solution.

Wilkey
 
I've spoken with the good folks at DOW Chemicals several times regarding PG.


The hygroscopic nature of pg means that it absorbs/adsorbs moisture until the cigars/ambient environment reaches equilibrium. Regardless of the concentration, the pg will work to maintain 70%. Xicar's pg solution is 90/10 (90% distilled water / 10% pg) and is marketed to maintain 70%. Increasing the water ratio just gives the pg more water to put into the air when needed but reducing the pg ratio means there's less pg to pull moisture from the air.


edit spelling
 
Mike,

Can your DOW connection provide vapor pressure curves for PG/water blends? If FoMoCo did his experiments in a controlled fashion, then his data reflect behavior I'd expect as typical of vapor pressure equilibrium behavior.

Wilkey
 
Here's a little extra food for thought. I pulled this chart from the 5th Edition of the Industrial Solvents Handbook, edited by F. W. Flick. This table shows the concentrations of PG in water solution that are in equilibrium with air. What's interesting is that to maintain 70% RH at 70F, the concentration is 66.5% PG, not 50%. In fact, by this table, 50% PG is in equilibrium with 82% RH air.

Table727.jpg


What IS curious is this curve, also from the same book. It shows that for solutions of ethylene glycol and water, 50% by weight around 70F gives around 70% RH. :0

Table710.jpg


I'm scratching my head on this one.

Wilkey
 
I'm glad you posted that Wilkey.

That was my concern....RH/Temp/Pressure....all have an effect on the numbers.

I'd go with Beads! :whistling:
 
Wilkey,
Thanks for posting that chart. At least you have confirmed that RH varies with PG and water concentration at a constant temperature.

Also, I noticed the table is by weight and not volume.
Molar mass PG = 76 g/mol
Molar mass water = 18 g/mol
Perhaps, it is closer to a 50/50 concentration by volume?
 
Well, density is the thing. The specific gravity of PG is 1.038 so weight and volume fractions are roughly in agreement. Not enough to make up the difference between 66% and 5% I believe.

Wilkey
 
FoMoCo said:
Wilkey,
Thanks for posting that chart. At least you have confirmed that RH varies with PG and water concentration at a constant temperature.
Click to expand...
Right. That's how I understand this process to work. Multicomponent solutions (e.g., water and PG., water and salt) must necessarily have a vapor pressure relationship (i.e., concentration in the liquid is related to the concentration in the air) that varies. That said, I recall reading somewhere that PG/water operates also by a surface tension effect. This would potentially alter the response. I can't find that link though.

Wilkey

PS. Ethylyene glycol is the toxic "brother" of PG and it is used in automobile antifreeze.
 
We scratch our heads because this is our hobby, a source of diversion and intrigue and some want to understand what's happening. Maybe to use that knowledge, maybe just to have it, but I'm a firm believer in the adage that the only stupid question is the one that doesn't get asked.

Wilkey
 
Ginseng said:
We scratch our heads because this is our hobby, a source of diversion and intrigue and some want to understand what's happening. Maybe to use that knowledge, maybe just to have it, but I'm a firm believer in the adage that the only stupid question is the one that doesn't get asked.

Wilkey
Click to expand...


Is this bikini too small for her?

EDIT - <----FIXED LINKY :D
 
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