DSC and DMA Measurements of an MBS Copolymer
Sample
Methlmethacrylate-butadiene-styrene (MBC) copolymer powder of unknown composition. The purpose of the analysis was to determine the glass transitions.
Conditions
Measuring cells: DSC821e and DMA/SDTA861e
Sample holder: DSC: 40 μl standard aluminum crucibles
DMA: shear sample holder
Sample preparation: DSC: 12.69 mg of the powder were placed in a crucible with pierced lid
DMA: The powder was pressed to 1.71-mm thick disks of 5.0-mm diameter. Two disks were mounted in the shear clamp.
DSC measurement: Heating from -100 to 150 °C at 29 K/min, with subsequent cooling from 150 to -100 °C at 5 K/min
DMA measurement: Heating from -100 to 180 °C at 2 K/min
Maximum force amplitude 10 N; maximum displacement amplitude 1 μm; offset control zero
The measurement was performed in a frequency series at 100, 10 and 1 HZ
Interpretation
Glass transitions are sometimes difficult to measure with calorimetric methods such as DSC. For example, often only one transition can be detected in copolymers that have a low content of one component. The DSC measurement of MBS shows the glass transition of the polybutadiene at -54.8 °C. Crystallization of the polybutadiene begins at - 20°C followed by melting. A second glass transition of the other copolymer components cannot be clearly seen in the measurement curve.
Conclusions
DMA is a better method to detect glass transitions, especially polymers. Often, it is difficult or even impossible to detect all the glass transitions by calorimetric methods. In such cases, dynamic mechanical analysis is the right choice. The DMA curve of the MBS copolymer shows only two glass transitions. This is due to the fact that the transition temperatures of the methyl methacrylate and the styrene components are very close and overlap each other and cannot be separated by these measurements.
DSC and DMA Measurements of an MBS Copolymer | Thermal Analysis Handbook No.HB252 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics