[EdMackey]

Firstly, I know nada about chemistry...so I'm seeking some info from folks who have the info. I'm a hobby woodworker (actually woodturner), and use polyurethane to finish my work. I usually purchase the poly in quart cans. After using just a small amount of poly and the level has gone down an inch or so, the poly gets a bit thicker and the results are not as good as they were when I first opened the can. I've been told that a product called Bloxygen (inert gas) can be squirted into the can as the level goes down and this will replace the layer of oxygen that sits over the poly. When the poly is in contact with oxygen, this facilitates evaporation, which causes the poly to degrade.

I'm also told by an old timer (excellent craftsman) that by breathing into the can just before closing it, does the same as squirting the inert gas. This would make sense if carbon dioxide is actually heavier than oxygen...
Anyone have any insight to this...

Thanks for any help on this..
Ed 

[AWK]

Density of CO2 is about 1.52 times greater than that of air

[lost and found]

Your breath is mostly nitrogen, but it does contain more CO2 than normal air. Breathing into the can will be better than nothing, but using a gas like argon would be the best. Any welder would have a tank of argon because it's used to protect the hot metal from oxygen.

MB

[billnotgatez]

interesting

http://www.bloxygen.com/faq.html

http://www.bloxygen.com/data.html

this is from a CPR site

How much good can it really do to breathe carbon dioxide into someone's lungs out of yours?

Normal air contains around 20% oxygen. A breath of air you exhale still contains over 15% oxygen so when it enters a victim's lungs, there is significant oxygen to be absorbed. The carbon dioxide mixed into your outgoing breath just comes right back out of the victim too.
Sure, they aren't getting as much oxygen as normal, but it's sure better than nothing.
 

[billnotgatez]

I do not think exhaling would help very much

[lost and found]

Now that I think about it some, you could easily make CO2 from baking soda. The classic baking soda and vinegar reaction produces bubbles of CO2.

NaHCO3 + CH3COOH --> CH3COONa + H2O + CO2

You could collect the CO2 in a balloon and then blow it into the can.

MB

[DrCMS]

Is this a moisture curing polyurethane you use?

If it is not just sealing the can up should stop the evaporation of the solvent and thickening up of the material.  I would be amazed if the material was degrading in air due to oxygen levels, water maybe but oxygen I doubt it.

If it is moisture curing then blowing into the can or making your own carbon dioxide as mentioned above would make things worse as they will contain water vapour.