E/VAC, Characterization by DSC and TMA

Sample

Ethylene-vinylacetate copolymer in the form of strips approx. 1.7-mm thick

Conditions

Measuring cell: DSC820 and TMA40, both with liquid nitrogen cooling options

Pan: Aluminum standard 40 μl for DSC, fused silica disks above and below the sample in the TMA

Sample preparation: DSC: punching a disk of 6-mm diameter, 20.117 mg

                                       TMA: punching a disk of 6-mm diameter that is placed between fused silica disks. Probe with 3-mm ball-point on the sandwich 

Measurement: First and second heating runs from -80 °C to 120 °C at 10 K/min Uncontrolled cooling to -80 °C

Load: 0.02 N

Atmosphere: DSC: Nitrogen, 50 cm³/min

                         TMA: Helium, 200 cm³/min 

Evaluation

Table of glass transition temperatures:

The DSC fusion peaks correspond to crystalline regions of the PE. Integration is performed from 0 to 110 using a straight baseline. Despite the different shapes, the heat of fusion is about the same, namely 89 J/g and 87 J/g respectively. Dividing this value by an assumed heat of fusion (100 J/g) for PE with such a low peak temperature gives a PE content of 82%. 

Conclusions

The DSC and TMA glass transition temperatures are different because the techniques measure different properties. The DSC heat of fusion allows the PE content to be estimated. More accurate determinations would be possible after calibration with known copolymers.

The TMA curves also yield the expansivity and a "heat distortion temperature" at which dimensional stability disappears.

_{E/VAC, Characterization by DSC and TMA | Thermal Analysis Handbook No.HB250 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics}