Determination of the Glass Transition by Means of the Expansion Curve - METTLER TOLEDO

Determination of the Glass Transition by Means of the Expansion Curve

Purpose

To determine the glass transition temperature according to the usual standard procedures

 

Sample

Cured KU600 epoxy resin powder formed as a cylinder, diameter 6 mm, height 1.92 mm.

 

Conditions

Measuring cell: TMA

Probe: Ball-point probe (quartz glass); diameter 3 mm

Sample preparation: The flat ends of the cylindrical sample were polished with fine sandpaper. Thin quartz glass disks were placed between the sample and probe and between the sample and sample support to distribute the force of the probe evenly over the entire cross-sectional area and so create a low compressive stress. 
The sample was heated in the TMA twice to demonstrate the relaxation effects on the first heating run.

TMA measurement: Heating from 40 to 160 °C at 5 K/min

Force on the probe: 0.02 N


Interpretation

The figure shows the same curves used in the previous example to calculate the expansion coefficient. In addition, the curve of the first heating measurement is displayed (dotted line). This shows that slight softening and possible thermal relaxation occur despite the careful sample preparation. As a result of this, the quartz disks are more uniformly pressed on the sample, so that the second heating curve measured with the same probe force is the normal expansion curve. 


Conclusions

TMA is an excellent method for determining the glass transition temperature, Tg, of filled or reinforced thermosets, and of large samples. Usually, special sample preparation is not necessary if the Tg can be determined from the second heating curve.

 

Determination of the Glass Transition by Means of the Expansion Curve | Thermal Analysis Handbook No.HB19 | Application published in METTLER TOLEDO TA Application Handbook Thermosets, Volume 1