TGA Measurements of Differently Vulcanized SBR Elastomers - METTLER TOLEDO

TGA Measurements of Differently Vulcanized SBR Elastomers

Purpose

The measurement of differently vulcanized SBR samples by TGA 

 

Sample

The samples are described in Section 4.2.2

 

Conditions

Measuring cellTGA/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 .

 

Interpretation

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.

 

Evaluation

The relative contents were determined from the TGA curve as described in Section 3.2.3. The following values can be determined:

  • Pyrolysis temperature: Temperature at half the step height of the decomposition step. 
  • Volatile components and elastomer content: Height of the pyrolysis step from the beginning of the measurement to about 500 °C 
  • Carbon black as pyrolysis product: Step height after switching the gases  
  • Ash

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/%. 

Conclusions

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