Determination of Softening by Penetration Measurements by TMA - METTLER TOLEDO

Determination of Softening by Penetration Measurements by TMA

Purpose

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.

 

Sample

Three different technical elastomers

 

Conditions

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.

 

Interpretation

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

 

Evaluation

 

Conclusions

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