Undrawn polyester monofil of 0.40_??_0.42mmφ was carrier-dyed with Disperse Red R and stretched by 5.1_??_5.2 fold. This filament shrunk freely by heating in water at T=50_??_170°C for 3min. and the change in D°fD (dichroic orientation degree), fx (X-ray orientation degree), and S (thermal shrinkage) were traced. Plotting these parameters against 1/T°K, the following results were obtained:(1) log S-1/T is linear and transition points are found at about 80°C, 140 and 150°C on that line.(2) fDD°-1/T is also linear and 3 “knicks” appeared at the temperatures corresponding to the above transition points.(3) S amounts to about 20% at maximum, when the dichroic orientation degree drops to 0.1 from 0.38, the initial orientatation degree, while fx is 0.93_??_0.92 and keep nearly unchanged.It is concluded that when the polyester monofilament (tetron) shrinks freely, the amorphous region disorients predominantly, while the crystalline orientation is kept nearly unchanged. The “knick” points on the log S-1/T line is meaningful, although the linear relation of log S-1/T has not been proved theoretically, and shrinkage proceeds discontinuously at the “knick” points.
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Okajima et al. (1966) studied this question.