Birefringence Changes During Retraction of Oriented Polystyrene Monofilaments. I. Changes of Average Birefringence

The changes in average birefringence during retraction have been measured at 85°C for four different oriented polystyrene monofilaments. The relationship between birefringence decay and length decrease is not linear: the birefringence decay is relatively more rapid than the length decrease, in all cases. Also, the birefringence-length relationship seems to be essentially independent of retraction temperature. Birefringence decay rate can be reduced by a factor of 1000 by not allowing the filament to retract. One of the filaments shows an interesting change in sign of the birefringence, from negative to positive, in the final stages of the retraction. The birefringence decay data for the four filaments could not be reduced to any universal curve by plotting either birefringence or relative birefringence against any simple functions of length or extension (all the filaments were made from the same polymer, so that a reduction to some such common basis should be possible). Analyzing the data in terms of a distribution of retardation times, by assuming that birefringence decay and length decrease are in some constant ratio for each retardation time (where the additional parameter, time, is introduced), also failed to reduce the data to a single common curve. Internal stress may be an essential parameter for a proper characterization of the birefringence.