Thermal Properties of Oriented PET

The X-ray scattering measurements revealed that the ordering process in oriented glassy states of PET are generated by a continuous structural change. Here, we will show the corresponding thermal properties observed by DSC. For the DSC measurements, we used the samples of oriented glassy PET that 

As shown in Fig. 6.8, the X-ray scattering patterns show that during the heating process from room temperature, no structural change was observed below Tg, while an ordering process occurs above Tg. In this sense, some mobility should be activated at Tg so that the ordering process starts in a similar way as the segmental motions are activated at Tg in the case of the 

In Fig. 6.11, it is also found that there are two regions where the total heat flow shows anomalous behavior, one is around 70° C and the other is between 110°C and 130°C. The latter one corresponds to the anomalous change in total heat flow observed at T g in Fig. 6.10. It can be expected that the observed upper shift of total heai flow at Tg is mainly due to the heat of crystallization. The position of this anomaly in Fig. 6.11 is different from that in Fig. 6.10. This may be due to the difference in heating rate (20K/min for DSC measurements in Fig. 6.10 and IK/min for TMDSC measurements in Fig. 6.11.) 

It should be noted that the temperature Tg where the step-like increase in total heat flow occurs in Fig. 6.10 increases with increasing Tq. This implies that the glass transition temperature of the oriented glassy states of PET increases as the structural order increases during the heating process. 

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