Epsilon caprolactam tends to polymerize in the catalytic amount of water (or base) and may be the reason for (un) usual behavior of the DSC curve. Material analysis after 180 C using IR spectroscopy can help in confirming the polymerization process.

Regards,

Milan.

Hello Milan,

thanks for this hint. Literature says that this reaction normally takes place from 250-300°C in an autoclave. But perhaps it starts earlier...

I did IR-Spectroscopy for samples with adding water until 150°C. There I saw no difference. Doing it again with the DSC samples is a good idea.

If polymerization would take place, why is there no melting peak in the second heating cycle (pink line) at around 220°C ?

Thanks a lot!

Regards

Michael

I agree, the characteristic peak for the melting point of nylon 6 is missing in the second cycle. However, the percentage of polymerization depends on the heating rate (see https://doi.org/10.1002/pat.3112) and may not be completed in the first cycle. What does the cooling curve look like in the second cycle? I had a similar situation with epsilon caprolactone and finally I concluded that polymerization is the reason. In any case, very interesting results.

Thanks for the discussion!

I can't have a look in this paper from home, but I have Khodabakhshi's PhD thesis (see https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiN3r73yJzdAhUFJVAKHdfmDfsQFjAAegQIARAC&url=https%3A%2F%2Fdspace.lboro.ac.uk%2Fdspace-jspui%2Fbitstream%2F2134%2F8369%2F1%2FKhosrow%252BKhodabakhshi-PhD-2011%255B1%255D.pdf&usg=AOvVaw2iksxDv9FnQrYHZZh-4mYX)

We can't really compare the results, because he had a mixture of e-CL with activator and catalyst, so polymerisation is initiated by the reactive components. And in his measurements, a peak in the secon heating showed up.

I saw a big difference in his DSC thermogramm of Caprolactam with a equal heating rate of 10K/min (his thesis, Fig. 5.15). I don't get a evaporation peak at this temperature. Mine occures from 150°C up to 274°C. A cooling curve is not included, so the effect of my DSC is not compareable.

Do you think a TGA with mass spectrometry could help?

Thanks in advance!