Strain-induced crystallization, Part IV: Induction time analysis

Abstract

The empirical equation, 1/t i = Ae Ei/RT , which expresses the exponential dependence of the reciprocal of crystallization induction time, t i , has been analyzed and shown to be equivalent to the nucleation rate equations derived earlier in Part III (1). Consequently we have used the t i measurements obtained earlier by Krueger and Yeh to calculate not only the nucleation rate enhancements but also the melting point elevations, the relative crystal thickness changes and molecular coil extension ratios of shear-crystallization polyethylene. It is shown that polyethylene when crystallized between 129 and 131°C at shear rates between 1.56 and 9.70 sec −1 can have melting point increases of 4.2 to 7.2°C and crystal thickness decreases of 20 to 25 percent, when compared to those crystallized at 130°C in the quiescent state. The predicted “coil” extension in the melt just prior to shear-induced crystallization ranges between 21 and 36 percent. The results of these analyses as well as those on nucleation rates of polyethylene oxide are discussed in detail.