PET, Cold Crystallization by Dynamic Load TMA

Sample

Disk of polyethylene terephthalate (METTLER TOLEDO tutorial sample kit)

Conditions

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

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

TMA measurement: Heating from 25 to 150 C at 10 K/min

Load: Changing every 6 s from 0.01 to 0.19 N

Atmosphere: Static air

Evaluation

The onset of the amplitude increase of 69.2 C corresponds to the glass transition temperature.

Interpretation

The low mean force of 0.10 N causes no visible indentation at the glass transition around 70 C. On the contrary, the sample becomes slightly thicker due to stress relief of the previously oriented film. Above the glass transition, the sample responds viscoelastically to the periodical force change.

Conclusions

Dynamic load TMA can be used to investigate the rather special thermomechanical properties of PET. DSC can of course also measure the glass transition and cold crystallization (see Application Example "PET, Thermal History"), but the DSC curves do not provide any information on mechanical behavior. 

_{PET, Cold Crystallization by Dynamic Load TMA | Thermal Analysis Handbook No.HB237 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics}