# Polyurethane turning into jelly?



## Barto (Apr 28, 2009)

Hi,

I've got a 4 liter can of oil based polyurethane and it is turning into a gel like substance. Has anybody ever seen this happen before? Is it just plain to old? I'm absolutely sure I closed the can properly.

Thanks heaps. Don't mind buying some more but still.


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## scrappy (Jan 3, 2009)

I've had some do that when it was in a clear jar. Put some in the jar to use for a job, (instead of handleing the large can) and after it sat for a few weeks with lid on tight, it had turned to gel. Really sick looking when it is still moveable but wont flow.haha

Not sure why, probably too old.

Scrappy


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## okwoodshop (Sep 15, 2009)

once the can is open and a little air gets to it, it gels after a few months or weeks depending on how much is left in the can. I have seen a product you can spray a gas in the can when closing it to remove the oxygen, never tried it so dont know how well it works.


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## Barto (Apr 28, 2009)

Thanks for your replies, but why does'nt (oil based) paint do this?


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## sbryan55 (Dec 8, 2007)

Bart, polyurethane works by bonding with oxygen to produce a polymer. Whereas oil base paint deposits a layer of pigments as the "oil" evaporates. Once the poly is exposed to oxygen in the air it starts to polymerize and the process is irreversible.

You can minimize this to a certain extent by transferring the remainder, when the can is opened, to smaller containers (i.e. mason jars) with a minimal headspace in the container. Other options include putting objects such as marbles in the opened can to reduce the amount of the airspace in the opened can. Another product that was mentioned by OKwoodshop is Bloxygen. I have never used this but it is supposed to work by displacing the air in the can with argon gas.

Another solution would be to buy smaller containers of poly if you are not going to be going through a gallon any time soon. It is more expensive to do this but you will be wasting less of the product by having smaller amounts on hand. Another option, if you use wiping poly, is immediately dilute the concentrated poly to a wiping solution with mineral spirits (50:50) when the can is opened. I have kept solutions over a year without the poly gumming up.


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## patron (Apr 2, 2009)

all of the above ,

or you can work more ,
and use it up faster !


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## Barto (Apr 28, 2009)

Gentlemen, Thanks very much for the explanation. All makes sense, guess I'll have to go for the smaller quantities. Hard for a Dutchman! Couple of dollars extra for a couple of liters (half a Gallon) more looks quite appealing!


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## patchy (Oct 6, 2008)

Barto, it is probably too late now and evrything will have gelled over BUT, what I do is to place a spoonfull of baking powder in a small jar or jug and then pour a little white vinegar in. You will see the co2 forming by the bubbling action. When you think that the action has ceased you can test the gas by lighting a taper and inserting it into the jar/jug - the flame on the taper should go out. That tells you there is little or no oxygen left in the jar/jug. 
Then simply tilt the jar/jug into the container of poly making sure that no liiquid flows in. The co2 will displace the oxygen above the poly or paint that you wish to save.
Those who have welding equip. can use a little argon or nitrogen for the same purpose.

patchy, British Columbia


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## Barto (Apr 28, 2009)

Hi patchy,

That is an excellent tip! I'm just about to buy another supply of Polyurethane and will certainly make use of your tip!


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## HokieMojo (Mar 11, 2008)

patchy,
are you saying to "pour" the CO2 into the can of poly? Is the CO2 heavier than air that it can be poured? I thought CO2 and oxygen mix relatively easily and one wouldn't settle out from the other. i'm intrigued by this, but i think I don't understand it right.


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## TopamaxSurvivor (May 2, 2008)

The carbon atom in CO2 should make it heaver than O2. So in small quanities, CO2 should dispalce O2.


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## stefang (Apr 9, 2009)

Wow! You can learn so much on this site. The jelly problem has troubled me for many years and it's so easy to solve with just a little baking soda and vinegar. Does it have to be white?


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## patchy (Oct 6, 2008)

a) HokieMojo, yes, co2 IS heavier than air, when you say that co2 and o2 mix fairly easily don't EVER go into a freshly painted confined space or partially confined space to find out!
b) Stefang, no, it does not have to be white, it just seems to be a cleaner solution (pun intended) - of,course you can always use ascetic acid.

Remember folks, this is a good way to keep ALL your canned/bottled paints/lacquers/ etc. in a useable form if you have containers with sufficient stuff left to make them worth keeping. All you are trying to do is keep oxygen from contacting the item in question. 
patchy, British Columbia


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## HokieMojo (Mar 11, 2008)

thanks Topamax and Patchy. I didn't know this. Very interesting.


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## TopamaxSurvivor (May 2, 2008)

You're welcome ) Mike, it shouldn't matter, acetic acid is in all vinegar.


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## TopamaxSurvivor (May 2, 2008)

I was just thinking, always a dangerous thing) A llttle shot form a small propane torch should displace the O2, its heavier than air.


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## Doctor50 (11 mo ago)

The molecular weight of gasses does not cause them to layer out in a container. Bloxygen is an expensive can of compressed argon. The company says that it works by forming a layer on top of the polyurethane, displacing the oxygen in the room air in the can. This does NOT happen. If you don't believe me, you can easily Google "diffusion of gasses" and see for yourself. Creating CO2 by reacting baking soda with vinegar produces heat that will result in its rapid diffusion. Unless it's liquid CO2, you can't "pour" it. Bloxygen can wash out the room air in a can, but you don't know how much you need as it depends on the unfilled space in your polyurethane can and the contents and pressure in the Bloxygen can, which you don't know. The company says to use a 2 second spray for quart cans and 5 seconds for a gallon can. That is totally inaccurate. At the very best, all that you can do is only wash out some of the oxygen and delay the polymerization, which causes the jelling of the polyurethane.


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## bilyo (May 20, 2015)

FWIW, I have tried the CO2 thing and have not had good success with it keeping the finish from gelling or skinning over. I have had good success putting left overs into double heavy duty ziplock bags. I then clean out the can and put the bag of finish into the can just so it will sit on the shelf and be easy to identify. There are also plastic bags with screw on lids called Stop Loss. They work well also and are reusable if you want to go to the trouble of cleaning them out.
https://www.amazon.com/Finishing-Solutions-LLC-StopLossBag-Pack/dp/B01LG5VVE6/ref=sr_1_1?crid=3IL49YOCPFHM1&keywords=stoplossbags&qid=1644460871&sprefix=stoploss%2Caps%2C1795&sr=8-1


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## EarlS (Dec 21, 2011)

> The carbon atom in CO2 should make it heaver than O2. So in small quanities, CO2 should dispalce O2.
> 
> - TopamaxSurvivor


Not quite correct since air is mostly (78%) nitrogen. However, CO2 is heavier than air so it will displace some of the air. However air currents cause the CO2 to mix with the air. That is why stuff like bloxygen (argon) is a compressed gas, plus it is a lot heavier than air. The velocity pushes the air out and the argon (inert gas) replaces the air.

IMO - the best solution is to buy smaller sizes of poly so you use it up before it sets up. Same thing with polyurethane glue. Even Titebond will set up if it sits around long enough. I've personally had all of them set up in the storage cabinet if they aren't used soon enough. That is also why they have a shelf life.


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## TopamaxSurvivor (May 2, 2008)

> The carbon atom in CO2 should make it heaver than O2. So in small quanities, CO2 should dispalce O2.
> 
> - TopamaxSurvivor
> 
> ...


 Over half a century since any chemical class. Sort of lost me there other than it won't work )

Do you believe propane could get a high enough concentration to displace the air? It normally releases at flammable concentrations of 4 to 9% +/-. Any air currrents would defeat the process, eh?


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## therealSteveN (Oct 29, 2016)

> Barto, it is probably too late now and evrything will have gelled over BUT, what I do is to place a spoonfull of baking powder in a small jar or jug and then pour a little white vinegar in. You will see the co2 forming by the bubbling action. When you think that the action has ceased you can test the gas by lighting a taper and inserting it into the jar/jug - the flame on the taper should go out. That tells you there is little or no oxygen left in the jar/jug.
> Then simply tilt the jar/jug into the container of poly making sure that no liiquid flows in. The co2 will displace the oxygen above the poly or paint that you wish to save.
> Those who have welding equip. can use a little argon or nitrogen for the same purpose.
> 
> ...


If it's in a pretty airtight container, simply turning the container upside down works well. Any O2 in the jar goes to the top. Your worst case is there will be a small amount at the new top, but everything at your new bottom is devoid of air. It's why those Stop Loss Bags work so well. Better if keep them hung upside down.


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## CaptainKlutz (Apr 23, 2014)

> ...polyurethane works by bonding with oxygen to produce a polymer. Whereas oil base paint deposits a layer of pigments as the "oil" evaporates. Once the poly is exposed to oxygen in the air it starts to polymerize and the process is irreversible. - Scott Bryan


Sorry, but this chemist must disagree with this incomplete description of the polyurethane curing?

--Begin chemistry lesson---

First some background:
What makes a polyurethane (PU) polymer unique is the existence of carbamate cross links. 
Most common compounds used to make PU finishing materials is OH terminated polymer and NCO terminated cross linker (usually called isocyanate). Carbamates can also be created with combination of chlorinated esters combined with amine or amide. Amine/Amide are less common in wood finishes as they tend to be high viscosity, produce hard crystalline polymers, and produce hydrochloric acid (HCL) as a byproduct. The amine/amide PU curatives are more often found in PU metal primers as the HCL can help clean/bond to metal. When you do find amine/amide in a wood finish, it usually is added to speed up cure on natural (pine) resin, and is called a PU varnish blend.

Oil based PU wood finish material is usually a blend of drying oil, conventional PU polymer/curative blend, and solvents.

All WW know that a drying oil (tung, linseed, etc) finish reacts/polymerizes by an oxidation (oxygen) reaction. But few know that during transition stage of curing, drying oils create OH terminations. Some of these OH sites react with PU curatives to bind the harder polymer from drying oil with softer PU polymer, into final polymer matrix.

PU polymer/curative reaction is not due oxidation. Intended cure mechanism for a single part PU, is isocyanate capped with a solvent material that inhibits the NCO termination from reacting with OH, until has been spread into a thin film on a surface and evaporates. But if the air contains moisture (H2O - and it always does), it replaces the blocking solvent, and opens the isocyanate to start the curing reaction. Hence, excess solvent evaporation and water exposure are the mechanism(s) that typically gel your can of PU finish.

The comparison to oil based house paints needs more detail as well: 
Modern oil based house paints contain alkyd resins, pigments, fillers, and solvents. These paint grade alkyd's are usually 'short oils', containing modified Drying Oils ( tung, linseed, etc). They cross link via similar oxidation method as other drying oil finishes. BTW - Many alkyd resins produce water as byproduct when cross linked, which is why (non-PU) oil based paints will not cure in colder temperatures, especially with high humidity.

--End chemistry lesson---

Hopefully, now you can understand how canned air products are designed to prevent and slow these reactions? They do this by containing; DRY nitrogen, or argon; containing no moisture. They also recommend expelling enough gas to displace the existing (wet) air in the can before sealing. However, this does not stop the solvent evaporation. When the PU can is nearly empty, the dry gas can still absorb solvents that are preventing the PU from cross linking. Which is why 'Stop Loss' bags or smaller containers with less surface area and space are useful; as you reduce amount of solvent evaporation.

Hope this helps. Thanks for reading to end.
Cheers!


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## controlfreak (Jun 29, 2019)

What works for me (with oil based paint anyway) is to pour a top 1/8" or 1/4" layer of whatever is used to thin the material on top of what is remaining. I don't stir it in or shake it. This new top solvent only layer replaces what may have evaporated in use and will off gas a bit to diminish the air that is in the top part of the can and act a a barrier. It is worth a shot I suppose.


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## zorro9 (Oct 15, 2020)

Have used Bloxigen for past 2 years, with good results. I take out what poly I need and spray the blox into the can with the lid almost closed.


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## dbw (Dec 2, 2013)

> Barto, it is probably too late now and evrything will have gelled over BUT, what I do is to place a spoonfull of baking powder in a small jar or jug and then pour a little white vinegar in. You will see the co2 forming by the bubbling action. When you think that the action has ceased you can test the gas by lighting a taper and inserting it into the jar/jug - the flame on the taper should go out. That tells you there is little or no oxygen left in the jar/jug.
> Then simply tilt the jar/jug into the container of poly making sure that no liiquid flows in. The co2 will displace the oxygen above the poly or paint that you wish to save.
> Those who have welding equip. can use a little argon or nitrogen for the same purpose.
> 
> ...


You can do all this OR you can simply store the can upside-down! There is still some O2 in the can but it affects only what's on the bottom. Bloxigen works as well.


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## OneDollarBob (Dec 30, 2021)

> ...polyurethane works by bonding with oxygen to produce a polymer. Whereas oil base paint deposits a layer of pigments as the "oil" evaporates. Once the poly is exposed to oxygen in the air it starts to polymerize and the process is irreversible. - Scott Bryan Sorry, but this chemist must disagree with this incomplete description of the polyurethane curing?
> 
> --Begin chemistry lesson---
> 
> ...


Did I read this correctly ? Low-humidity increases solvent based poly's cure time and high-humidity decreases it ?


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## Peteybadboy (Jan 23, 2013)

I was looking into Bloxigen. I have had success by putting glass beads into the can to displace the air.


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