To measure a typical TGA curve of natural rubber.
Unvulcanized NR
Measuring cell: TGA/SDTA851e
Pan: Alumina 30 µl
Sample preparation: Piece of rubber of approx. 20 mg
TGA measurement: Heating from 50 °C to 625 °C under nitrogen (50 ml/min) and then from 625 °C to 850 °C under air (50 ml/min), Heating rate 30 K/min
Atmosphere: Nitrogen then air, automatically switched
The DTG curve shows that the pyrolysis of NR takes place in two steps: a main step, which is the origin of the DTG peak at about 400 °C, and a small secondary step seen as a shoulder at somewhat higher temperature (about 450 °C). On switching from nitrogen to air, the TGA curve shows practically no combustion of carbon, indicating that no carbon black was formed during pyrolysis. Volatile compounds vaporize at lower temperature before pyrolysis begins.
The evaluation of the individual steps is summarized in the following table:
NR pyrolyzes at relatively low temperatures (395 °C). The main pyrolysis step is followed by a small step at about 460 °C whose height is about 7% of the main step. A small amount of carbon black remains after pyrolysis. The ash content can also often be neglected.
TGA of Natural Rubber (NR) | Thermal Analysis Handbook No.HB426 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2