Identification of BR and NBR using a TGA-FTIR Combination
Purpose
BR and NBR are difficult to distinguish from one another by thermal analysis alone. One possibility of differentiating between these two polymers is to use a combined technique such as TGA-FTIR.
Sample
Technical NBR and BR elastomers
Conditions
Measuring cell: TGA/SDTA851e connected to a Nicolet Nexus FTIR spectrometer by a heated transfer line.
Pan: Alumina 70 µl
Sample preparation: Pieces of approx. 20 mg (NBR) and 30 mg (BR)
TGA measurement: Heating from 50 °C to 700 °C under nitrogen (50 ml/min) Heating rate 10 K/min
Atmosphere: Nitrogen
The diagram displays the TGA and DTG curves of the NBR and BR samples.
Evaluation
The pyrolysis of NBR and BR takes place in practically the same temperature range. On the basis of the pyrolysis alone, it is not possible to identify the polymer concerned.
NBR differs from BR in that it has a nitrile group. In the infrared (IR) spectrum, the nitrile group absorbs in the range 2260-2180 cm-1 . The absorption band cannot always be identified with certainty in the IR spectrum under typical TGA-FTIR measurement conditions because it is sometimes of low intensity and is in any case close to the CO2 absorption bands. In such cases, it is advantageous to evaluate the chemigram recorded with data from the wavenumber range of interest. In simple terms, the IR absorption in this wavenumber range is continuously integrated and plotted as a function of temperature (or time).
The diagram displays the DTG curve and the chemigram for the wavenumber range 2260-2180 cm-1 . In the BR measurement, no peak was observed in the chemigram during pyrolysis. It follows that none of the volatile compounds evolved contained a nitrile group. With NBR, the pyrolysis peak in der DTG curve corresponds to the peak observed in the chemigram. This nitrile absorption indicates that the material pyrolyzed contained a nitrile group. This confirms that is was NBR.
Conclusions
An analysis of the evolved gases with an online TGA-FTIR combination is a useful technique to identify the type of elastomer measured. If the IR absorption intensity is low, as in the above case of NBR, sensitivity can be increased by evaluating the chemigram of the wavenumber range of the characteristic absorption bands of interest.
Identification of BR and NBR using a TGA-FTIR Combination | Thermal Analysis Application No. HB462 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2.