Abstract We investigate the influence of controlled uniaxial extension on various flow induced phenomena in semidilute solutions of ultra high molecular weight polyethylene (UHMwPE). Concentrations range from 9 w% to 29 w% and the choice of solvent is paraffin oil (PO). The start-up extensional behavior is measured at various Hencky strain rates ε ˙ and at two different temperatures ( 150 ∘ C and 170 ∘ C ) well above the melting point. At ε > 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 ∘ C at high ε ˙ and high concentrations. Scenario 1, observed at both temperatures, is most pronounced at low rates and/or high concentrations.
- Extensional flow