[buffer]

I would like to do some thermal analysis on polymer composites and a quick look at TGA protocols online shows that the analysis is done under nitrogen and in some cases under air. What factors determine the environment the analysis is done in?

[Stepan]

TGA in Nitrogen will show you transformation (drying, decomposition) of polymer in inert atmosphere. Air is used if you need to test a TGA profile in contact with air. You may expect to see effect of moisture, oxygen and sometimes CO2 (if polymer has alkaline groups).

[marquis]

 Here is a very common example.  If you want to determine the amount of carbon black filler in the rubber, you would use nitrogen atmosphere.  The carbon black won't burn off, and by using the correct temperature profile, you can find out how much was added.  Ditto with oils, etc.

If you want to find out what inorganic fillers were added, you use air.  The polymer and different additives burn off at different temperatures.  You can often track the additives by the weight difference between the temperatures, as they burn off.  And the final weight will tell you the amount of filler (clay, zinc oxide, etc.) present.

[Stepan]

Here is a very common example.  If you want to determine the amount of carbon black filler in the rubber, you would use nitrogen atmosphere.  The carbon black won't burn off, and by using the correct temperature profile, you can find out how much was added.  Ditto with oils, etc.

Could you please explain how it works or give a reference on the method. Thank you

[marquis]

The rubber and many oils are pyrolyzed or volatilized at lower temperatures than carbon black.  By setting your temperature range correctly (and that can sometimes take some trial and error to do), you can get rid of everything but the carbon black.  That is, assuming a nitrogen atmosphere. 

Some procedures will have you cool the oven and then heat the carbon black up in an air atmosphere to get another check on carbon black content.

As for references.  The manufacturer of our TGA had all the temperature profiles set up for us with the instrument.  I think a TGA manufacturer would be your best bet. 

For a technical reference, try " Analysis of Rubber and Rubber Like polymers", third edition, edited by W.C. Wake, B.K. Tidd, and M.J.R. Loadman.  Pages 230 to 250 will get you started. 

I recommend reading the whole book, if you will doing a lot of elastomer work.

Good luck.