The brittle temperature is the point at which an elastomer becomes hard on cooling or softens on heating. With most elastomers, this occurs around the temperature range of the glass transition. The softening of elastomers cooled to below their glass transition temperatures can be measured in TMA heating experiments. The penetration of a ball-point probe into the sample with a load of 0.1 N is measured as a function of temperature.
Three different technical elastomers
Measuring cell: TMA40
Probe: Ball-point probe (quartz glass)
Sample preparation: Parallel plates with a thickness of 2 mm or 4 mm cut as cubes from the starting material.
TMA measurement: Equilibration for 10 min at –100 °C, then heating from –100 °C to 50 °C at 5 K/min
Load: 0.1N
Atmosphere: Nitrogen, 200 ml/min
The TMA curves show the relative penetration depth of the ball-point probe with reference to the initial sample thickness as a function of temperature.
The TMA signal of the sample first increases linearly due to the thermal expansion of the glassy material. As the material softens, the probe penetrates into the sample. The onset of softening can be determined as the point of intersection of two tangents. The brittle temperature is defined as the temperature of the peak maximum of the first derivative curve
TMA penetration measurements can be used to measure the softening of materials. The softening temperature can be characterized by the onset temperature of the TMA curve or the maximum of its derivative. The onset temperature is always somewhat lower than the first derivative temperature.
Determination of Softening by Penetration Measurements by TMA | Thermal Analysis Application No. HB 488 | Application published in METTLER TOLEDO TA Application Handbook Elastomers Volume 2