Dynamic Mechanical Analysis of PET

Sample

Three different PET films; sample A crystallizes slowly; sample B has so-called low viscosity and sample C has standard viscosity.
The measurements were performed to characterize the physical transitions and to compare behavior during melting and crystallization.

Conditions

Measuring cell: DMA/SDTA 861^e with the shear sample holder

Sample preparation: Two disks, 0.94-mm thick of 5-mm diameter were mounted in the shear sample holder.

DMA measurement:

1. The shear measurement was performed at 1 Hz from -140 °C to 280 °C at a heating rate of 2 K/min. Maximum force amplitude 25 N; maximum displacement amplitude 5 μm, offset control zero.
2. The comparison measurements were performed at 10 Hz from 25 to 280 °C at a heating rate of 2 K/min followed by cooling to 100 °C at 2 K/min. Maximum force amplitude 3 N; maximum displacement amplitude 30 μm offset control zero. 

Atmosphere: Static air

Interpretation

The PET sample A was measured using DMA program 1. The curves in the first diagram show the behavior of PET over the whole temperature range. At sub-ambient temperatures, the secondary relaxation can be observed. This β-relaxation corresponds to small-scale movements of molecular segments. This effect is small in comparison to the main relaxation (glass transition) observed at 80 °C.

_{Dynamic Mechanical Analysis of PET | Thermal Analysis Handbook No.HB238 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics}