PVC-U, Thermal Stability - METTLER TOLEDO

PVC-U, Thermal Stability

Sample

Unplasticized PVC film supplied in the set of samples of the German "Arbeitsgemeinschaft Deutsche Kunstsoff-Industrie"

 

Conditions

Measuring Cell: TGA850 with sample changer

Pan: Alumina 70 μl, without lid

Sample preparation: Disks cut with scissors: 8.937 mg (5 K/min),

                                 8.558 mg (10 K/min), 8.974 (15 K/min) and 

                                  8.935 mg (20 K/min)

TGA measurement: Heating from 25 °C at 5, 10, 15 and 20 K/min respectively. Final temperature 500 °C

Atmosphere: Nitrogen, 50 cm3/min

 


Evaluation

The evaluation according to ASTM E 1641 calculates temperatures corresponding to certain conversions, e.g. 10%. A maximum value of 20% should be considered since the function of conversion would cause errors in the calculated thermal stability. Evaluating with Model Free Kinetics would yield good predictions for extents of decomposition >20%. This example is based on 5% decomposition (i.e. a 3.15% decrease in mass)


According to ASTM E 1641, predictions for the thermal endurance are made using a first order kinetic model because the error of calculation is small below 20% decomposition. Normally the predictions are made for the conversion that has been used in the calculation of kinetic data. As the diagram shows, reaction times (time to failure) can be calculated for other conversions, α, eg of 10%


Conclusions

The thermal endurance is estimated on the basis of four TGA curves measured at heating different rates. ASTM E 1641 assumes a rate of decomposition that decreases with decreasing temperature according to Arrhenius. There is a risk of errors arising through extrapolation. A countermeasure is the use of very low heating rates with correspondingly low decomposition temperatures. To save time, only the measurement with the highest rate is run to complete decomposition. All others are stopped as soon as a threshold value of 5% is reached. 

 

PVC-U, Thermal Stability | Thermal Analysis Handbook No.HB221 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics