Aliphatic Polyurea Coating (Posted to the wrong forum before) 2

[metalman8357]

Hi everyone,

Quick question here. I work for a company that owns a coating company used for construction. One of the products we offer is aliphatic polyurea, which can be painted onto concrete or steel as a sealant. We've had problems with the material failing on job sites, and we've sent out samples of our product to a third party lab to test tensile strength and % elongation. We report 450% elongation and 3200 psi on our spec. sheet, but the third party testing found 12% and a tensile strength of 3200 psi. Clearly something isn't right here so I have a few questions:

1.) My understanding is that aliphatic polyurea is a very flexible material and is considered an elastomer. 450% elongation seems more correct than 12%. I called the test lab and he said the material he received was already cured and very hard like a plastic. This doesn't seem right, but the tensile strength was there. Also, we test this to ASTM D2370 instead of ASTM D412...which one is more correct? Also, if we had a test sample that was 40 mils thick and pulled at 20 in/min vs. a 0.125" thick sample pulled at 2 in/min, should our % elongation still be pretty much the same value?

2.) Is aliphatic polyurea considered an thermoset elastomer or a thermoplastic elastomer?

3.) If we did in fact supply the correct material, how could it be possible to see 12% elongation. Is it possible for something to go wrong with the reaction to produce these results?

Any help would be much appreciated!

 

[TVP]

ASTM D2370 is specific for coatings, and is the appropriate standard. D412 is for rubber materials (bulk). Polyurea coatings should be flexible and elastomeric. If the testing was performed correctly, then it indicates excessive cross-linking, incorrect mixing, etc. The following is an excellent review of the various technologies employed in these types of coatings:

http://madisonchemical.com/madison_resources/downloads/tech_coatingsworld2003.pdf

 

[metalman8357]

Super informative, thank you TVP!

 

[TomDOT]

I really don't think that you'll see that big a difference between the two methods. If you originally used D2340 for the qualification testing, you should keep using D2340 for batch-to-batch checks.

Different thicknesses and different pull rates can give you different results, how different varies from material to material. Typically faster pulls give you lower elongation and higher tensile strength. This difference seems excessive.

If your elongation is THAT far off, you have something significantly wrong with the coating. If you don't have the expertise inhouse, I would call in a failure expert on coatings.

If I were investigating, I would likely start with an FTIR comparison of the problem material against a known good sample. You need someone who is skilled at interpretation of coating spectra, not just an instrument jockey.

We don't have enough information here to really figure out what happened.