PET sticky residue when heating with steam

[pro_cube]

Hello everyone

I am seeing sticky residue leech from PET sleeves being subjected to steam at 126 - 128 C. I have two supplies of PET - it only appears to come from one (sleeve "A"). I have FTIR spectra for the residue, and the two sleeves.

The residue, and one of the sleeves (A) have much higher absorbance in the following, compared to the other sleeve (B):

1730 cm-1 : stretching of C=O of carboxylic acid group

1240 cm-1 : terephthalate group

And the residue & sleeve A, have less absorbance than sleeve B for:

712 cm-1 : interaction of polar ester groups and benzene rings

Please can someone with polymer knowledge shed light on what the differences in these absorbance means for the stability of the PET? For example does it make sleeve A much more susceptible to breakdown from acid/alkali conditions, less stable to heat, other reagents...

Thanks for your help!

 

[pro_cube]

I should perhaps add that I did not see this sticky residue for years until now with sleeve A, and I am struggling to find out what the root cause may be. Unless the sleeve supplier has changed their raw materials (which they are claiming they have not). I'm hoping to try and get some old sleeves analysed, if they can be found.

 

[btrueblood]

At that temperature, it sounds like hydrolysis. There may be some metal salts in/on one of the sleeves acting as a catalyst, that is not present on the other one.