Self-Nucleation of Polymers with Flow: The Case of Bimodal Polyethylene

Abstract

A small amount of high molecular weight molecules can have a dramatic influence on the flow-induced crystallization kinetics and morphology of polymers. In this paper, it is shown that with the addition of 7 wt % of high molecular weight molecules a melt of low molecular weight polyethylene can be tailored for process-induced self-nucleation. To ensure mixing between molecules of high and low molecular weight, we make use of a special synthesis route where both fractions are generated simultaneously by two catalysts immobilized on the same support. Under the influence of flow, the high molecular weight molecules make crystallization possible at temperatures as high as 137 °C, where the matrix alone cannot crystallize. Moreover, flow can lead to fibrillar precursors of crystallization at temperatures as high as 142 °C, i.e., in the vicinity of the equilibrium melting point. On cooling below 139 °C, these precursors crystallize and transform into shishes while the growth of kebabs is still suppressed becaus...