propylene glycol source

I found a possible source of propylene glycol today at the local convenience / drug store and wanted to solicit opinions on its suitability as a medium for stock solutions. It's Pitt-Penn Premium RV Antifreeze -50. The MSDS is at http://www.pittpenn.com. They also make a -100 version of the same product. This is sold as an antifreeze for water systems in RVs (recreational vehicles or motorhomes).

pH on the -50 is 8.5-9.5, on the -100 it's 9.4-10.3. Specific gravity is 1.030 on the -50 and 1.057 on the -100. Other contents are dipotassium phosphate and water, no specific %, but the -100 is said to be at least 96% propylene glycol. For comparison, The Chemistry Store MSDS for propylene glycol states 99% purity and a specific gravity of 1.038.

So my question is this: At $3.99 a gallon, is this a bargain, and suitable for photographic use as a non-oxidizing medium for stock solutions? Is the specific gravity (relative to the 99% version) any indication that there's too high a percentage of water in the mix to keep well?

I'm no chemist, but this is looking like a good option compared to $16.50 + shipping on 9 lbs.

Thanks for any advice.

Lee

Patrick Gainer's March/April 2004 piece in Photo Techniques was entitled "The Role of Antifreeze in Photographic Science." He describes creating the "A" part of a two-stock solution from ethylene glycol antifreeze, and then goes on to say that propylene glycol is safer. It's unclear from that article whether he's actually used propylene glycol antifreeze in this role (perhaps he'll chime in). Others certainly have done so; I've seen posts about it and I've done it myself. I used Prestone LowTox Antifreeze/Coolant to create part A of the split-stock solution Gainer describes. This was almost three months ago, and I developed a roll of film in the resulting developer just a few days ago with no problems. The MSDS for the Prestone product (available here) claims it's "90-100%" propylene glycol and "0-0.5%" sodium tolyltriazole, but I don't know any more about its composition than this.

Despite my positive experience with the anti-freeze, I can't claim that an additive in either the Prestone or the Pitt-Penn product won't cause problems with some or even many formulas. Basically, you're adding unknown components to your developer. With luck, they'll be photographically inert, but I doubt if anybody can promise they actually will be. So far the anti-freeze seems fine for me, and as you say, the cost savings over shipping a purer form is substantial.

srs5694 said:

Patrick Gainer's March/April 2004 piece in Photo Techniques was entitled "The Role of Antifreeze in Photographic Science." He describes creating the "A" part of a two-stock solution from ethylene glycol antifreeze, and then goes on to say that propylene glycol is safer. It's unclear from that article whether he's actually used propylene glycol antifreeze in this role (perhaps he'll chime in). Others certainly have done so; I've seen posts about it and I've done it myself. I used Prestone LowTox Antifreeze/Coolant to create part A of the split-stock solution Gainer describes. This was almost three months ago, and I developed a roll of film in the resulting developer just a few days ago with no problems. The MSDS for the Prestone product (available here) claims it's "90-100%" propylene glycol and "0-0.5%" sodium tolyltriazole, but I don't know any more about its composition than this.

Despite my positive experience with the anti-freeze, I can't claim that an additive in either the Prestone or the Pitt-Penn product won't cause problems with some or even many formulas. Basically, you're adding unknown components to your developer. With luck, they'll be photographically inert, but I doubt if anybody can promise they actually will be. So far the anti-freeze seems fine for me, and as you say, the cost savings over shipping a purer form is substantial.

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Thanks. I have the Gainer article on hand, and am hoping Pat and others with more chemistry knowledge than I will chime in.

I found the RV water system antifreeze completely by chance when I was looking for a standard engine cooling version of propylene glycol. When I've asked for it in that application in these parts, I get responses that infer that only idiots use it, and that the merchants wouldn't stoop to carry such a product.

I see the Prestone product you used has no water listed, but I wonder if that's a difference in the MSDS requirements between the US and Canada. Just wanted some more knowledgeable input before I dump a lot (in monetary terms) of phenidone or other expensive powders into it and have it go south for some reason I didn't properly anticipate.

Besides, my wife is out of town for another week and it's an ideal time to stink up the microwave.

Lee

I have bought propylene glycol (99%) from a company that sells commercial refrigeration equipment and supplies. Maybe there's such a business near you.

Lee L said:

So my question is this: At $3.99 a gallon, is this a bargain, and suitable for photographic use as a non-oxidizing medium for stock solutions? Is the specific gravity (relative to the 99% version) any indication that there's too high a percentage of water in the mix to keep well?

I'm no chemist, but this is looking like a good option compared to $16.50 + shipping on 9 lbs.

Thanks for any advice.

Lee

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Short answer: yes, it will work just fine. I bought a gallon of similar prop-gly antifreeze from a local auto-parts store for about the same price, and it worked great. You may want to go buy another gallon. It's falling out of fashion as anti-freeze, according to my auto parts guy who says that according to the people who run the oil/antifreeze changing places, the p-g stuff is actually more toxic AFTER USE than the ethylene glycol stuff. Don't know if that's true, but since it's relatively non-toxic in its out-of-the-bottle state, it works just fine for film developer.

Larry

Larry,

Thanks for the response. The version I'm looking at is slightly different stuff, designed for the drinking water supply pipes in RV's for winter storage, to keep them from freezing and bursting. Given the toxicity of ethylene glycol, I don't see this particular product going away, and expect it will remain available. I'm more concerned about the water content (oxidation) and the possible effects of dipotassium phosphate on photographic processes.

Obviously this or a similar form of propylene glycol must be widely available for RV owners, and I thought that it might be an additional and cheaper form for people to use if it's suitable for use with photochemistry.

And thanks to John S for the refrigeration tip. I'll look into it.

Lee

I think that statement that propylene is more toxic after use than ethylene glycol is made by those who have ethylene for sale. What factor in the use of either of these could change the toxicity? I'm asking, not telling, but I don't know of any.

The 96% figure may be due to the other ingredients. The glycols tend to take up water from the atmosphere, but that's true of even the purest. I have not tested to see how much water is required to affect the oxidation rate of a glycol stock solution, but I did leave a thin layer of stock exposed in a jar lid of about 4" diameter for 30 days and it was then about as active as when I first poured it out. I described this experiment in the article.

The $3.99 is a good price. How many gallons of stock solution will you be using per year at a rate of about 1/3 ounce per roll or 8X10 sheet? At that price, though, you need not worry about doing some experiments. Use 100 ml of it for an experiment. With that and a rounded tablespoon of ascorbic acid and about 1/4 teaspoon of phenidone (or amidol if you happen to have it) you can soon find out if it works at all. Chances are that heating enough to dissolve the solids will get rid of most of the water. You can leave some of the stock exposed as I did to get an idea of its keeping qualities.

The pH of the water solution of the antifreeze is probably a little on the basic side because of corrosion inhibitors. You're not likely to see the difference because you will only be using 10 or 20 ml per liter of working solution. Your tap water might have that much alkali in it.

JFYI:
Propylene Glycol Solution
(% by mass) 0 10 20 30 40 50 60
Specific Gravity - SG - 1) 1.000 1.008 1.017 1.026 1.034 1.041 1.046
Freezing Point
Temperature (oF) 32 26 18 7 -8 -29 -55
Temperature (oC) 0 -3 -8 -14 -22 -34 -48

Thanks Pat y Pablo,

Did some more searching this morning.

The Peak folks talk about acute and chronic toxicity in EG and PG, both before and after use, here: http://www.peakantifreeze.com/tech/tech_a.html

and about typical RV antifreeze here:
http://www.peakantifreeze.com/tech/tech_g.html

Other topics are covered by clicking on the topic headings at the bottom of these pages.

Their summary on toxicity is that PG is less toxic to humans and most animals before use, and that any post-use toxicity from heavy metal contamination in the cooling system is not "worse" in PG than in EG. Nothing in PG changes to make it inherently more toxic than EG, and the toxicity added in use is the same in both. So PG is less toxic overall than EG both before and after use.

The Peak pages indicate that the -50F rating for RV antifreeze is achieved with under a 35% solution, so that they typically have up to 65% water as supplied. The MSDS for the Pitt-Penn version shows Ca. 100% volatile by volume for the -50F and "not determined" for the -100F version. If you leave out the other additives, titrisol's data shows the SG of the -50F version at 1.03 to be halfway between a 30% and a 40% solution, making this approximately 65% water. Water is volatile, so I guess it's considered so for the purposes of an MSDS, and so the 100% volatile won't help with establishing dilution rates.

Maybe I'll keep searching for an "undiluted" PG antifreeze source locally. I doubt I can find the -100F version of RV antfreeze locally, which should be on the order of 96% or better PG. I already have TEA for PC-TEA. My aim here is to find a stock solution medium.

Thanks to all,
Lee

I called around and found a store nearby that carries Prestone Low-Tox antifreeze. (Didn't ask the price.) I looked up the MSDS here: Dead Link Removed

Looks like this has SG of 1.046 ( a 60% solution with titrisol's numbers, discounting other additives), but the MSDS in section XII indicates that it's a 40% solution of 1,2-PROPANEDIOL.

This is within 5% of the RV -50 antifreeze dilution, so maybe I'll give the RV stuff a test run. I'll be completely swamped in a few weeks running through December, so long term testing will be hard to accomplish.

I'm still interested in hearing any comments or suggestions on using the RV stuff from those with more chemistry knowledge than I.

Thanks to all for your input,
Lee

My first foray into propylene glycol use had me get some swimming pool anti-freeze that was listed as 100% PG. It was thin in viscosity and had a blue tint to it. I didn't know the difference as it was my first exposure to it but I think it added to some crooked trails I initially took in applying it to my first experiments. I'm just relating this as an example that trusting labeling from applications that aren't likely hyper-sensitive to slight variations may not be worth a couple of bucks spent in getting it through more trusted sources.

craigclu said:

<snip> ... I think it added to some crooked trails I initially took in applying it to my first experiments... <snip>

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Exacty what I was hoping to avoid by asking for input. The -50F RV antfreeze seems pretty thin in the bottle and appears as a standard to have a pink dye in it.

Did you have problems with stability, poor results, inconsistency? If you learned anything specific of value, I'd like to hear it. If the RV stuff can function properly, it would be nice for people to have a local and cheaper supply option.

Thanks,
Lee

Hi Lee -- I haven't read the thread in detail but I am a chemist and can perhaps offer a bit of advice.

The automotive-use propylene glycol will probably work just fine for Gainer-style developers. The water content is probably fairly low, and in any case, as Pat mentioned earlier, glycols tend to be very hygroscopic (they absorb moisture from the air). I would be a little concerned about the phosphates in the antifreeze. It probably won't make a huge difference unless there is a lot of calcium in your water supply. You can use distilled water to avoid this.

A few years ago I went looking for propylene glycol antifreeze and couldn't find any in central Boston. A fellow at the auto-supply store where I lived at the time (Cambridge, MA) told me that he simply doesn't sell much of the stuff because it is more expensive than ethylene glycol-based products. The big-box auto supply stores would only sell it to me in 5-gallon units. So I ended up buying a quart of it from the Chemistry Store, and I still have lots of it left. I mixed up about 500 ml of PC-Glycol stock solution (Pat Gainer's recipe) in October 2003 and have been using it ever since, with no loss of activity. Since 20 ml makes up 1 L of working solution, it'll be a while before I need more propylene glycol.

I keep repeating this; but, chemicals are cheap, film is expensive!

It seems that antifreeze mixtures can contain some water. The whole purpose of using propylene glycol is to have a waterless solvent as an aid to preventing oxidation. Other compounds such as disodium phosphate can have unknow effects.

I think the best bet is to buy propylene glycol and be done with it. For example, a gallon of propylene glycol from The Chemistry Store is $16.38 + shipping. Considering the small amount used per roll, this should last the average user for quite some time.

Jordan said:

.......and in any case, as Pat mentioned earlier, glycols tend to be very hygroscopic (they absorb moisture from the air).....

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Since the point is to have a water-free solvent, is it feasible to remove the absorbed water in propylene glycol by heating?

John -- The only really efficient way to do it would be to heat the stuff under a vacuum.

As long as propylene glycol is open to the air, it will absorb water vapour from it. Although I'm not sure exactly how much water is in the antifreeze-grade propylene glycol, it really is those phosphates that give me concern.

The amount needed to mix up Pat Gainer's developers really is minimal. As Gerald says, just buy it from the Chemistry Store. You will eliminate a lot of variables that could influence your results. A little propylene glycol goes a long way.

Point of information-please.

What's the difference between Diethylene Glycol and Propylene Glycol?

Glycols are mainly used in the paint industry to regulate drying time and surface gloss. The lower the evaporation rate, the longer the drying time. Many glycols are miscible with water over a great range of proportions, giving the manufacturer flexibility in terms of regulating drying times. The cheapest source are suppliers that sell glycols to these industries, but standard packaging is 55 gl. drums. If you find a paint factory or a body shop (it is also used in automotive lacquers) near you, chances are they can sell you a liter or a gallon for your purposes. I`ve worked with propylene glycol and ethylene glycol (monomethyl ether) and prefer the latter. I`ve never used it in film developers, but I have used for screen printing with Dektol and it worked great.

garryl said:

Point of information-please.

What's the difference between Diethylene Glycol and Propylene Glycol?

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They are two different substances. Chemically -- Diethylene glycol is HOCH2CH2OCH2CH2OH while propylene glycol is CH3CHOHCH2OH, if that means anything to you.

Diethylene glycol is not the same as ethylene glycol, and neither are the same as polyethylene gycol.

I think that some commercial liquid concentrates, like HC-110, use diethylene glycol as a solvent. If you can get your hands on it inexpensively, it'd probably work as a substitute in the Gainer-type developers.

Propylene Glycol is often used in humidors. It has a property where is stabilizes humidity to a certain point by absorbs excess humidity (down to that point) and releasing water (up to that point).

The food grade Propylene Glycol I once bought was clear (about $5 a pint at Walgreens). All the RV anti-freeze Propylene Glycol I've seen and used is tinted. I don't know how the tinting dye might effect use as a developer.

When I used it as an antifreeze in the toilet of a cabin (in case of freezing) it did stain the bowl.

YMMV

mgb74 said:

.

When I used it as an antifreeze in the toilet of a cabin (in case of freezing) it did stain the bowl.

YMMV

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Ah come on! Your blaming the anti-freeze?

Thank for the Diethylene answer guys. I've seen it in many old formulas and wondered about the composition.

Jordan said:

They are two different substances. Chemically -- Diethylene glycol is HOCH2CH2OCH2CH2OH while propylene glycol is CH3CHOHCH2OH, if that means anything to you.

Diethylene glycol is not the same as ethylene glycol, and neither are the same as polyethylene gycol.

I think that some commercial liquid concentrates, like HC-110, use diethylene glycol as a solvent. If you can get your hands on it inexpensively, it'd probably work as a substitute in the Gainer-type developers.

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The chemistry store sells dipropylene glycol as well as propylene glycol. I don't know the chemcial difference but funtionally they appear to be the same because Pyrocat-HD solutions mixed with both types of glycol gave virtually the same results.

Sandy

mgb74 said:

The food grade Propylene Glycol I once bought was clear (about $5 a pint at Walgreens).

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Where was this stocked in Walgreens, and for what purpose was it sold? Was it sold under a particular brand name? $5.00/pint is identical to The Chemistry Store's price for small quantities ($10.00/quart), and there'd be no shipping, so this sounds like an appealing source, but somehow I doubt if the average teenage Walgreens clerk would where to find the propylene glycol.

Well, I kept exploring the possiblity of getting propylene glycol locally. Going from the post in this thread mentioning Walgreens, I went to a relatively nearby location. I couldn't find it on the floor anywhere and went to the pharmacy window to ask about where it was stocked.

The person at the counter said she could order it for me, but couldn't give me a firm price. She said that the markup would probably put it at about $10, so I asked the quantity. She started indicating quantity by spreading her hands apart and adjusting the distance. I figured either she thought I might be too stupid to understand metric, or that she might not understand it, so given the $10 estimated price and the $5 price for a pint quoted in this thread, I asked, "for a liter?" She seemed relieved and said "about a liter".

When I went to pick it up the next day, it turned out to be a pint (473ml) and the price was $8.99 + tax. Not a bargain, not exactly highway robbery. I told the pharmacist at the pickup window that they should really hire people for a pharmacy who know that a pint is not "about" a liter. However, I did manage to score enough pharmacy grade to test with locally, and with a 24 hour delivery time. If you ask your local pharmacist, you might get some that way as well, but try to get someone who can give you a price and volume up front.

I don't get my prescriptions there. You've gotta wonder about their dosing accuracy. SRS's fears about the teenaged clerks were well-founded.

Lee