Polymer, Vol.136, 215-223, 2018
Extension induced phase separation and crystallization in semidilute solutions of ultra high molecular weight polyethylene
We investigate the influence of controlled uniaxial extension on various flow induced phenomena in semidilute solutions of ultra high molecular weight polyethylene. Concentrations range from 9 w% to 29 w% and the choice of solvent is paraffin oil. The start-up extensional behavior is measured at various Hencky strain rates epsilon and at two different temperatures (150 degrees C and 170 degrees C) well above the melting point. For Hencky strains epsilon > 0.9 the qualitative behavior of the samples differ significantly depending on the imposed conditions and the concentration of the samples. Overall we propose two flow scenarios: Scenario 1 - flow induced phase separation resulting in an unstable bulky filament and Scenario 2 - flow induced phase separation and crystallization resulting in a stable deformation and a smooth strongly strain hardening filament. Scenario 2 is observed only at 150 degrees C at high epsilon and high concentrations. Scenario 1, observed at both temperatures, is most pronounced at low rates and/or high concentrations. (C) 2017 Elsevier Ltd. All rights reserved.