I am trying to confirm the polymer composites of three different drive belts from a car engine. I think two of them are made from EPDM and one from a highly saturated nitrile rubber. Can you confirm this from the specrtra provided and point out relevant values?
edit: Note; car engine drive belts often have a fibreglass thread inside to increase stregnth and durability
Dear Ash, the quality of the spectra is not very good (maybe bad contact with the ATR crystal). If you write "epdm ir spectrum" to google and look at the pictures you can see several examples.
Article Maleic Anhydride Grafting on EPDM: Qualitative and Quantitat...
shows EPDM and non-grafted EPDM. Some of the frequencies agree, but the intensity distribution is quite different.The presence of the OH band and the broad bands may indicate the presence of fillers. See also https://www.ssi.shimadzu.com/products/literature/ftir/ftir%20a416.pdf
Another attached file shows spectra of nitrile rubber samples
See also: Article Maleic Anhydride Grafting on EPDM: Qualitative and Quantitat...
http://shodhganga.inflibnet.ac.in/bitstream/10603/27890/9/09_chapter%204.pdf shows EPDM neoprene blends but it is not really useful as most of the bands are saturated
Another attached file contains FTIR data on silica filled EPDM
Finally I did not see any convincing nitrile band anywhere only noise
In general the ATR spectra are more sensitive in the low frequency range as the probing depth is inversely proportional to the frequency (in the order of the evanescent wavelength). The presence of carbon black may indeed cause a blurring of the spectrum.
Accurate IR spectral identification of carbon-filled (black) rubbers requires employing ATR crystals having sufficiently high refraction indices. The spectra you show have probably been recorded using a diamond crystal.
The main difficulty in obtaining clear spectra originates from the fact that black rubbers have a relatively high refraction index, which is close to that of diamond. Consequently, there is no ATR effect and obtained spectra are often heavily distorted. Owing to a high refraction index, thus allowing shallower penetration, germanium is the preferred ATR crystal in the analysis of black rubbers.
Everything said above by Prof. Sobecki - is correct.
Yet, to my surprise, I was able to obtain the FTIR-ATR spectra of rubbers filled with 60% of carbon black - of passable quality. Of course Ge possessing refractive index around 4 - seems to give better quality of spectra. But - Ge is very brittle (and costly) - so there is a good chance before you learn how correctly to use Ge elements of internal reflection - you will break several crystals. I advice you to make some more attempts with Diamond Crystal
I used Ge crystal many years ago in a relatively old, grating type equipment. The Ge crystal was relatively large (about 5 cm long, 2 cm wide and about 0,5 cm thick with 45o slopes at the ends). The sample holder consisted of two parallel metal plates which could be screwed together. I investigated plastic films so I put the film on one plate, then came the crystal and the other metal plate screwed together. It was a flat geometry so it was not dangerous for breaking the cyrstal. I preferred it ti KRS5 which is not only extremely toxic but being soft, is very sensitive to any scratching, therefore the background deteriorated fast. Now if I would have an ATR spectrometer I would select ZnSe crystal if possible. (Another problem with Ge is that the cutoff frequency is about 800 cm-1 - so you lose information).
All the 3 materials used in ATR method: KRS-5, Diamond and ZnSe have very close refractive indices - appr. 2.4 (Ge appr. 4). In my research in case of rather rigid materials I prefer KRS-5 [yes, it is rather soft and easily scratched; since it is prepared of mixed salt TlBr x TlJ - it is toxic and thus should be re-polished by using special technique]. But I do not recommend you to use ZnSe - because according to my experience the spectra obtained employing ZnSe - give distorted broadened bands. I have no explanation why (?), but it is a true experimental fact. Of the above listed materials for ATR - I still advice you to use KRS-5. (or much thinner -for 20 reflections 2.5 mm Ge)
Best Regards,
Leonid
The quality of the spectra is not too good. Perhaps you can re_scan it
With high noise interference, it is not advised to interpret the results which may lead to improper conclusions. So analyze the sample again and get clear spectra. More peaks in group frequency region deteriorates the results.
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