Visible dichroism of the poly(ethylene terephthalate)–disperse dye system at high temperatures

摘要

AbstractThe 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 factorDversus 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 ofDchange reversibly with the temperature. Hence, if a change inDafter 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 withTg, although theTgcan hardly be observed after the cold crystallization; some phenomena reported in the literature are proposed as evi