PVC, TMA Curves as a Function of Applied Load

Sample

Disk of polyvinyl chloride of approx. 3-mm diameter

Conditions

Measuring cell: TMA40 with 3-mm ball-point probe

Pan: The sample is placed on a fused silica disk of 6-mm diameter and 0.5-mm thickness

Sample preparation: Each measurement was performed with a new sample

TMA measurement: Heating from 30 to 130 °C at 5 K/min

Load: 0.01 N, 0.1 N, 0.5 N, 1 N and 2 N. For each measurement, a new PVC disk was used. Loads >0.5 N were obtained by using additional weights

Atmosphere: Static air

Evaluation

This intersection points of the tangents drawn at 60 and 76 °C and the mean expansivity α_mean, between 40 and 50°C are summarized in the table. For the sake of clarity, the individual evaluations are not shown in the figure. 

The expansivity can only be measured essentially free of the effects of compression when low forces are used. With higher forces, the compressive stress would have to be evenly distributed over a large cross-sectional area by placing a fused silica disk between sample and ball-point probe.

Conclusions

TMA measurements with a ball-point probe give reproducible softening temperatures that are practically independent of the applied load. With higher loads of e.g. 0.5 N, the intersection point is better defined due to the greater angle between baseline and tangent. 

_{PVC, TMA Curves as a Function of Applied Load | Thermal Analysis Handbook No.HB222 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics}