Analysis of Elastomers with Different Types of Carbon Black
Purpose
Carbon black is an active filler. Its activity is influenced primarily by its surface area. Very often, therefore, it is not just the content but also the type of carbon black used as filler that is of interest. Samples of EPDM containing different types of carbon black filler are used show the extent to which TGA can provide this information.
Sample
Elastomer made from EPDM with different types of carbon black:
EPDM content: 49.3%
Carbon black content: 44.3%
Vulcanization system and additives: 6.3%
The value of DBP compressed (DBP measured under pressure) describes the size of the carbon black surface area (better than the void volume) under conditions that simulate the production process. The determination of the DBP compressed value is a standard method for the determination of the surface area. The smaller the DBP compressed value, the smaller the surface area.
Conditions
Measuring cell: TGA/SDTA851e
Pan: Alumina 30 µl
Sample preparation: Two pieces of elastomer of equal size totaling about 10 mg for each measurement
TGA measurement: Heating from 50 °C to 625 °C under nitrogen (50 ml/min), Heating from 50 °C to 625 °C under nitrogen (50 ml/min), Heating and cooling rates are 10 K/min
Atmosphere: Nitrogen and air, automatically switched
Pyrolysis of the polymer takes place in the first part of the measurement under nitrogen. This step is a prerequisite for the actual carbon black analysis – an evaluation is, however, not necessary for the measurements described here. The carbon black then burns in the second heating step performed under air. It can be seen that the combustion of carbon black occurs at different rates.
Evaluation
The step height of the carbon black combustion is between 44.0% and 44.5% and agrees with the formulation (44.3%). A measure of the combustion behavior is the temperature at half the step height, T1/2 , (midpoint). As the following diagram shows, this temperature correlates well with the DBP value used to characterize the surface area of the carbon black.
Comments
The correlation between the combustion temperature, T1/2 , and the type of carbon black is best when DBP compressed is used to characterize the carbon black structure. The DBP value often used shows a poor correlation.
Conclusions
The TGA measurement program described above allows different types of carbon black fillers used in elastomers to be distinguished.
Analysis of Elastomers with Different Types of Carbon Black | Thermal Analysis Application No. HB456 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2