The measurement of differently vulcanized SBR samples by TGA
The samples are described in Section 4.2.2
Measuring cell: TGA/SDTA851e
Pan: Alumina 70 µl
Sample preparation: Pieces of elastomer of approx. 10 mg
DMA measurement: Heating from 35 °C to 600 °C under nitrogen (50 ml/min), and then from 600 °C to 850 °C under air (50 ml/min) Heating rate 10 K/min
Atmosphere: Nitrogen then air, automatically switched .
With sulfur cross-linked elastomers, a higher degree of vulcanization produces an elastomer network that is less stable at high temperatures. This has to do with the catalytic effect of sulfur radicals formed on decomposition, which accelerate the degradation of the elastomer. Pyrolysis of the elastomer is complete at about 500 °C. After switching from nitrogen to air, there is a slight decrease in mass. This is due to the combustion of small amounts of carbon black formed during pyrolysis.
The relative contents were determined from the TGA curve as described in Section 3.2.3. The following values can be determined:
The effect of sulfur content on the pyrolysis temperature is shown in the following diagram. A linear relationship between the pyrolysis temperature, Tp, and the sulfur concentration, αS, was found In the concentration range investigated:
The extrapolated pyrolysis temperature for a sample that does not contain any sulfur,Tp0, is 448.5 °C. The slope, b, is 4.41 K/%.
About 95.5% of the sample is degraded during pyrolysis; 1.5% carbon black is formed. The ash residue is 0.5% larger than the content of white zinc. This difference is due either to an elastomer decomposition product or to the presence of other additives. The pyrolysis temperature of the elastomer decreases with increasing sulfur content.
TGA Measurements of Differently Vulcanized SBR Elastomers | Thermal Analysis Application No. HB445 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2