Influence of Pressure on the TGA of an NR/SBR Blend

Purpose

In Section 4.6.1. The influence of the heating rate on oil content determination an oil-containing elastomer based on an NR/SBR blend was analyzed at different heating rates. The same material is now measured under vacuum.  

Sample

Vulcanized elastomer (sample E) with the following composition:

Conditions

Measuring cell: TGA/SDTA851^e

Pan: Alumina 30 μl

Sample preparation: Piece of elastomer of approx. 20 mg

TGA measurement: Heating from 50°C to 625°C at 10 K/min at 1000 mbar and 50 ml/min nitrogen, and at 10 mbar (vacuum, with 20 Nml/min nitrogen purge for balance). 

Atmosphere: Nitrogen, at 1000 mbar and 10 mbar  

Evaluation

The TGA curves were evaluated with the aid of the DTG curve. The results are summarized in the following table. The temperatures marked with an (M) are the midpoints of the step evaluation. The other temperatures are peak maximum temperatures of the DTG curves.

Interpretation

The DTG curve shows that the oil vaporizes at lower temperatures in vacuum, but that polymer pyrolysis occurs at almost the same temperature. The pyrolysis steps of the two polymer components are also better separated in vacuum. The reason for this is that gaseous decomposition products diffuse more rapidly out of the sample at reduced pressure. 

The oil content can be accurately determined under vacuum. The resolution of the measurement under vacuum at 10 K/min corresponds to that of the measurement under normal pressure at 2 K/min (see Section 4.6.1. The influence of the heating rate on oil content determination).

Conclusions

Measurements under reduced pressure allow the plasticizer (oil) and polymer constituents of elastomers to be determined relatively rapidly and with good accuracy. Separation of the residue into carbon black and ash, however, requires measurement in an oxidizing atmosphere. 

_{Influence of Pressure on the TGA of an NR/SBR Blend | Thermal Analysis Application No. HB 482 | Application published in METTLER TOLEDO TA Application Handbook Elastomers Volume 2}