VISIBLE DICHROISM OF POLY (ETHYLENE TEREPHTHALATE)-DISPERSE DYE SYSTEM AT HIGH TEMPERATURES

The dichroic behavior of PET film dyed at 70°C with Disperse Red 17 or Disperse Yellow 7 was investigated in the temperature range 20–200°C with a view to studying the changes in amorphous region of PET at high temperatures. The dichroic orientation factor D versus temperature plot is expressed by a straight line with negative slope; two breaks appear at 80 (Tg) and 120°C. So long as the amorphous structure does not change irreversibly, the values of D change reversibly with the temperature. Hence, if a change in D after heating is observed at room temperature, it is evidence that an irreversible change occurred in the amorphous structure during the heating. The break at 120°C is a new amorphous transition point of PET existing along with Tg, although the Tg can hardly be observed after the cold crystallization; some phenomena reported in the literature are proposed as evidence. Copyright © 1969 John Wiley & Sons, Inc.