Crystallization of an ethylene-based butene plastomer: the effect of uniaxial extension

Abstract

In this paper, the effect of uniaxial extension on the crystallization of an ethylene-based butane plastomer is examined by using rheometry coupled with differential scanning calorimetry (DSC). Uniaxial extension experiments were performed at temperatures below and above the peak melting point of the polyethylene in order to characterize its flow-induced crystallization behavior at extensional rates relevant to processing. The degree of crystallinity of the stretched samples was quantified by DSC, i.e., by analyzing the thermal behavior of samples after stretching. Analysis of the tensile strain-hardening behavior very near the peak melt temperature revealed that crystallization depends on temperature, strain, and strain rate. In addition, it was revealed that a very small window of temperatures spanning just 1–2°C can have a dramatic effect on polymer crystallization. Finally, flow-induced crystallization experiments at temperatures close to the peak melting point have shown the recrystallization of multiple crystalline structures within a polymer matrix, witnessed by double peaks within a narrow window of 89–93°C in the DSC thermographs, with the most demonstrable double peak behavior occurring at a temperature of 91°C, a temperature that is just 1°C cooler than the peak melt temperature of the polymer.