Retraction of Oriented Polystyrene Monofilaments

Abstract

When oriented polystyrene monofilaments are heated to temperatures in the neighborhood of the transition temperature they retract to an unoriented state at conveniently measurable rates. Curves of length as a function of time have been measured at five different temperatures (75°–95°C, at 5° intervals) for two filaments with different initial amounts of orientation. When the retraction curves are plotted as length vs log time, it is found that the curves at different temperatures are not superposable by lateral shift along the logarithmic time scale, as would be true for simple viscoelastic behavior. Activation energies calculated from these curves are a function of time as well as of temperature; the activation energy at any given temperature tends to level out to a final constant value with increasing time, however. The rate of change of activation energy with time increases with increasing temperature, so that the final value is attained more quickly; the final value also decreases systematically with increasing temperature. Final activation energy values increase rapidly with decreasing temperature in this region and are very high (300 kcal at 75°). It is postulated that specific volume changes are responsible for the time-dependent activation energies observed in these experiments. It is also of interest that these experiments appear to isolate the viscoelastic mechanism involving molecular configuration change from that involving local molecular distortions.