PMMA, Glass Transition - METTLER TOLEDO

PMMA, Glass Transition

Sample

Plexiglas pane, 4 mm thick
(polymethylmetacrylate, PMMA)

 

Conditions

Measuring cell: DSC821e

Pan: Aluminum standard 40 μl, pierced lid

Sample preparation: Disks sawn from the pane and suitable pieces cut off with a knife, 15.4 mg

DSC measurement: First run from 40 to 200 °C at 10 K/min, cooling at 5 K/min,
                                 second run from 40 to 200 °C at 10 K/min

Atmosphere: Nitrogen, 50 cm3/min

 

Evaluation

The midpoints of glass transition temperatures are 103.3 C (first run) and 101.4 C (second run).

 

Interpretation

PMMA is completely amorphous and has a glass transition temperature of approx. 105 C. The first measurement curve is nearly always influenced by relaxation phenomena. If the thermal history is eliminated, the shape of the DSC curve becomes more or less ideal. In the curve shown above, the relaxation peak appears before the actual glass transition. It can however also overlap the glass transition region directly or appear afterward (see for example PET)

 

PNMA, Glass Transition | Thermal Analysis Handbook No.HB239 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics