The role of a secondary process in polymer crystallization: 4 − Polyethylene revisited

Abstract

AbstractIt is suggested that the overlap of primary and secondary crystallization is a cause of the repeated observation of non‐integer n values in polymer crystallization. The possibility that two concurrent crystallization processes occurring during the crystallization of polyethylene may account for anomalous fractional values of the Avrami exponent, of no theoretical significance, is reconsidered using data from the classical paper by Banks et al. (Polymer 4: 61 − 74 (1963)) on the kinetics of crystallization of polyethylene fractions which placed emphasis on evaluating the secondary crystallization stage. In general constant n values in excess of that expected for the crystallization mechanisms can readily be interpreted in terms of the additional crystallinity developed by the secondary process and these values increase commensurate with the rate constant of secondary crystallization. Constant n values close to but below n = 4.0 are interpreted as due to the presence of an induction period present in the presence of homogeneous nucleation. It is not possible to separate the effect of incorporating both an induction period, lowering the value of n, and secondary crystallization, raising the value of n, in the kinetic equation. © 2017 Society of Chemical Industry